This document presents an analysis of transit spectroscopy observations of three exoplanets - WASP-12 b, WASP-17 b, and WASP-19 b - using the Wide Field Camera 3 instrument on the Hubble Space Telescope. The observations achieved almost photon-limited precision but uncertainties in the transit depths were increased by the uneven sampling of the light curves. The final transit spectra for all three planets are consistent with the presence of a water absorption feature at 1.4 microns, though the amplitude is smaller than expected from previous Spitzer observations possibly due to hazes. Due to degeneracies between models, the data cannot unambiguously constrain the atmospheric compositions without additional observations.
This document presents a sample of 151 dwarf galaxies that exhibit optical spectroscopic signatures of accreting massive black holes. The sample was identified by systematically searching ~25,000 emission-line galaxies from the Sloan Digital Sky Survey with stellar masses comparable to or less than the Large Magellanic Cloud. Many of the galaxies show narrow-line signatures of black hole accretion, and some also exhibit broad H-alpha emission, indicating gas orbiting in the deep potential of a massive black hole. This increases the number of known active galaxies in this low stellar mass range by over an order of magnitude. The median stellar mass of the host galaxies is around 108.5 solar masses, around 1-2 magnitudes fainter than previous samples of
The yellow hypergiant HR 5171 A: Resolving a massive interacting binary in th...GOASA
HR 5171 A exhibits a complex appearance based on AMBER/VLTI observations. The observations reveal an unusually large star of approximately 1315 solar radii at a distance of 3.6 kiloparsecs. The source is surrounded by an extended nebula. The observations also show a high level of asymmetry in the brightness distribution, which is attributed to the discovery of a companion star located in front of the primary. Analysis of visual photometry data indicates the system has an orbital period of 1304 days, providing evidence it is a contact or over-contact eclipsing binary. Modeling suggests a total system mass of 39-79 solar masses and a high mass ratio of at least 10 for the companion. The discovery of the
Rapid formation of large dust grains in the luminous supernova SN 2010jlGOASA
This document summarizes observations of rapid dust formation in the luminous supernova SN 2010jl over multiple epochs from 26 to 868 days past peak brightness. Analysis of emission line profiles shows increasing extinction over time, indicating continuous dust formation. The extinction curve implies the presence of very large (>1 micron) dust grains. Thermal emission models suggest dust temperatures declining from 2300K to 1100K over time, requiring carbonaceous rather than silicate dust. Combined extinction and emission data indicate a dust mass of ~0.0025 solar masses at 868 days, growing rapidly and expected to reach ~0.5 solar masses by 8000 days if production continues. The results provide evidence for very efficient and rapid dust formation in the dense
The green valley_is_a_red_herring_galaxy_zoo_reveals_two_evolutionary_pathwaysSérgio Sacani
This document summarizes research using data from Galaxy Zoo, SDSS, and GALEX to study how star formation is quenched in low-redshift galaxies. The key findings are:
1) Taking galaxy morphology into account, the "green valley" is not a single transitional state, as was previously thought.
2) Only a small population of blue early-type galaxies rapidly transition across the green valley as their morphology transforms from disk to spheroid and star formation is quenched quickly.
3) The majority of blue star-forming galaxies have significant disks and retain their late-type morphology as their star formation rates decline very slowly.
4) Different evolutionary pathways are observed for early- and late-type
“A ring system detected around the Centaur (10199) Chariklo”GOASA
- The Centaur object (10199) Chariklo was observed to occult a star, revealing the presence of two narrow rings around the object.
- The rings have widths of about 7 km and 3 km, and orbital radii of 391 km and 405 km from the center of Chariklo.
- Evidence supports the rings being composed of water ice and their geometry explaining the dimming and changing spectrum of Chariklo observed between 1997 and 2008. The discovery of rings around a minor planet is a first for the Solar System.
Kepler-1647b is the largest and longest-period Kepler transiting circumbinary planet discovered to date. It orbits an eclipsing binary star system with an orbital period of approximately 1100 days, making it one of the longest-period transiting planets known. The planet is around 1.06 times the size of Jupiter and perturbes the times of the stellar eclipses, allowing its mass to be measured at 1.52 times that of Jupiter. Despite its long orbital period compared to Earth, the planet resides in the habitable zone of the binary star system throughout its orbit. The discovery of this unusual planetary system provides insights into theories of planet formation and dynamics in multiple star systems.
Beyond the Kuiper Belt Edge: New High Perihelion Trans-Neptunian Objects With...Sérgio Sacani
We are conducting a survey for distant solar system objects beyond the Kuiper
Belt edge ( 50 AU) with new wide-field cameras on the Subaru and CTIO tele-
scopes. We are interested in the orbits of objects that are decoupled from the
giant planet region in order to understand the structure of the outer solar sys-
tem, including whether a massive planet exists beyond a few hundred AU as first
reported in Trujillo and Sheppard (2014). In addition to discovering extreme
trans-Neptunian objects detailed elsewhere, we have found several objects with
high perihelia (q > 40 AU) that differ from the extreme and inner Oort cloud
objects due to their moderate semi-major axes (50 < a < 100 AU) and eccen-
tricities (e . 0.3). Newly discovered objects 2014 FZ71 and 2015 FJ345 have
the third and fourth highest perihelia known after Sedna and 2012 VP113, yet
their orbits are not nearly as eccentric or distant. We found several of these high
perihelion but moderate orbit objects and observe that they are mostly near Nep-
tune mean motion resonances and have significant inclinations (i > 20 degrees).
These moderate objects likely obtained their unusual orbits through combined
interactions with Neptune’s mean motion resonances and the Kozai resonance,
similar to the origin scenarios for 2004 XR190. We also find the distant 2008
ST291 has likely been modified by the MMR+KR mechanism through the 6:1
Neptune resonance. We discuss these moderately eccentric, distant objects along
with some other interesting low inclination outer classical belt objects like 2012
FH84 discovered in our ongoing survey.
This document presents a sample of 151 dwarf galaxies that exhibit optical spectroscopic signatures of accreting massive black holes. The sample was identified by systematically searching ~25,000 emission-line galaxies from the Sloan Digital Sky Survey with stellar masses comparable to or less than the Large Magellanic Cloud. Many of the galaxies show narrow-line signatures of black hole accretion, and some also exhibit broad H-alpha emission, indicating gas orbiting in the deep potential of a massive black hole. This increases the number of known active galaxies in this low stellar mass range by over an order of magnitude. The median stellar mass of the host galaxies is around 108.5 solar masses, around 1-2 magnitudes fainter than previous samples of
The yellow hypergiant HR 5171 A: Resolving a massive interacting binary in th...GOASA
HR 5171 A exhibits a complex appearance based on AMBER/VLTI observations. The observations reveal an unusually large star of approximately 1315 solar radii at a distance of 3.6 kiloparsecs. The source is surrounded by an extended nebula. The observations also show a high level of asymmetry in the brightness distribution, which is attributed to the discovery of a companion star located in front of the primary. Analysis of visual photometry data indicates the system has an orbital period of 1304 days, providing evidence it is a contact or over-contact eclipsing binary. Modeling suggests a total system mass of 39-79 solar masses and a high mass ratio of at least 10 for the companion. The discovery of the
Rapid formation of large dust grains in the luminous supernova SN 2010jlGOASA
This document summarizes observations of rapid dust formation in the luminous supernova SN 2010jl over multiple epochs from 26 to 868 days past peak brightness. Analysis of emission line profiles shows increasing extinction over time, indicating continuous dust formation. The extinction curve implies the presence of very large (>1 micron) dust grains. Thermal emission models suggest dust temperatures declining from 2300K to 1100K over time, requiring carbonaceous rather than silicate dust. Combined extinction and emission data indicate a dust mass of ~0.0025 solar masses at 868 days, growing rapidly and expected to reach ~0.5 solar masses by 8000 days if production continues. The results provide evidence for very efficient and rapid dust formation in the dense
The green valley_is_a_red_herring_galaxy_zoo_reveals_two_evolutionary_pathwaysSérgio Sacani
This document summarizes research using data from Galaxy Zoo, SDSS, and GALEX to study how star formation is quenched in low-redshift galaxies. The key findings are:
1) Taking galaxy morphology into account, the "green valley" is not a single transitional state, as was previously thought.
2) Only a small population of blue early-type galaxies rapidly transition across the green valley as their morphology transforms from disk to spheroid and star formation is quenched quickly.
3) The majority of blue star-forming galaxies have significant disks and retain their late-type morphology as their star formation rates decline very slowly.
4) Different evolutionary pathways are observed for early- and late-type
“A ring system detected around the Centaur (10199) Chariklo”GOASA
- The Centaur object (10199) Chariklo was observed to occult a star, revealing the presence of two narrow rings around the object.
- The rings have widths of about 7 km and 3 km, and orbital radii of 391 km and 405 km from the center of Chariklo.
- Evidence supports the rings being composed of water ice and their geometry explaining the dimming and changing spectrum of Chariklo observed between 1997 and 2008. The discovery of rings around a minor planet is a first for the Solar System.
Kepler-1647b is the largest and longest-period Kepler transiting circumbinary planet discovered to date. It orbits an eclipsing binary star system with an orbital period of approximately 1100 days, making it one of the longest-period transiting planets known. The planet is around 1.06 times the size of Jupiter and perturbes the times of the stellar eclipses, allowing its mass to be measured at 1.52 times that of Jupiter. Despite its long orbital period compared to Earth, the planet resides in the habitable zone of the binary star system throughout its orbit. The discovery of this unusual planetary system provides insights into theories of planet formation and dynamics in multiple star systems.
Beyond the Kuiper Belt Edge: New High Perihelion Trans-Neptunian Objects With...Sérgio Sacani
We are conducting a survey for distant solar system objects beyond the Kuiper
Belt edge ( 50 AU) with new wide-field cameras on the Subaru and CTIO tele-
scopes. We are interested in the orbits of objects that are decoupled from the
giant planet region in order to understand the structure of the outer solar sys-
tem, including whether a massive planet exists beyond a few hundred AU as first
reported in Trujillo and Sheppard (2014). In addition to discovering extreme
trans-Neptunian objects detailed elsewhere, we have found several objects with
high perihelia (q > 40 AU) that differ from the extreme and inner Oort cloud
objects due to their moderate semi-major axes (50 < a < 100 AU) and eccen-
tricities (e . 0.3). Newly discovered objects 2014 FZ71 and 2015 FJ345 have
the third and fourth highest perihelia known after Sedna and 2012 VP113, yet
their orbits are not nearly as eccentric or distant. We found several of these high
perihelion but moderate orbit objects and observe that they are mostly near Nep-
tune mean motion resonances and have significant inclinations (i > 20 degrees).
These moderate objects likely obtained their unusual orbits through combined
interactions with Neptune’s mean motion resonances and the Kozai resonance,
similar to the origin scenarios for 2004 XR190. We also find the distant 2008
ST291 has likely been modified by the MMR+KR mechanism through the 6:1
Neptune resonance. We discuss these moderately eccentric, distant objects along
with some other interesting low inclination outer classical belt objects like 2012
FH84 discovered in our ongoing survey.
We present deep optical images of the Large and Small Magellanic Clouds (LMC and SMC) using
a low cost telephoto lens with a wide field of view to explore stellar substructure in the outskirts
of the stellar disk of the LMC (r < 10 degrees from the center). These data have higher resolution
than existing star count maps, and highlight the existence of stellar arcs and multiple spiral arms in
the northern periphery, with no comparable counterparts in the South. We compare these data to
detailed simulations of the LMC disk outskirts, following interactions with its low mass companion,
the SMC. We consider interaction in isolation and with the inclusion of the Milky Way tidal field.
The simulations are used to assess the origin of the northern structures, including also the low density
stellar arc recently identified in the DES data by Mackey et al. (2015) at ∼ 15 degrees. We conclude
that repeated close interactions with the SMC are primarily responsible for the asymmetric stellar
structures seen in the periphery of the LMC. The orientation and density of these arcs can be used to
constrain the LMC’s interaction history with and impact parameter of the SMC. More generally, we
find that such asymmetric structures should be ubiquitous about pairs of dwarfs and can persist for
1-2 Gyr even after the secondary merges entirely with the primary. As such, the lack of a companion
around a Magellanic Irregular does not disprove the hypothesis that their asymmetric structures are
driven by dwarf-dwarf interactions.
Detection of solar_like_oscillations_in_relies_of_the_milk_way_asteroseismolo...Sérgio Sacani
Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens
of thousands of field stars. Tests against independent estimates of these properties are however
scarce, especially in the metal-poor regime. Here, we report the detection of solar-like
oscillations in 8 stars belonging to the red-giant branch and red-horizontal branch of the globular
cluster M4. The detections were made in photometric observations from the K2 Mission
during its Campaign 2. Making use of independent constraints on the distance, we estimate
masses of the 8 stars by utilising different combinations of seismic and non-seismic inputs.
When introducing a correction to the Δν scaling relation as suggested by stellar models, for
RGB stars we find excellent agreement with the expected masses from isochrone fitting, and
with a distance modulus derived using independent methods. The offset with respect to independent
masses is lower, or comparable with, the uncertainties on the average RGB mass
(4 − 10%, depending on the combination of constraints used). Our results lend confidence to
asteroseismic masses in the metal poor regime. We note that a larger sample will be needed
to allow more stringent tests to be made of systematic uncertainties in all the observables
(both seismic and non-seismic), and to explore the properties of RHB stars, and of different
populations in the cluster.
The document summarizes the discovery of transient bright features detected in Titan's northern sea, Ligeia Mare, by the Cassini spacecraft's radar instrument in July 2013. These features were not seen in previous or subsequent observations. The author analyzes potential explanations and argues that the features were likely ephemeral phenomena caused by surface waves, bubbles, or suspended solids. This suggests dynamic processes are starting in Titan's northern lakes and seas as summer approaches in the northern hemisphere.
The canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
This document reports the discovery of a newly discovered optical Einstein ring (ER) called the "Canarias Einstein Ring". It was discovered serendipitously in imaging data from the Dark Energy Camera. Follow-up spectroscopy with the Gran Telescopio CANARIAS confirmed the nature of the system, with the lens being an early-type galaxy at a redshift of z=0.581 and the source being a starburst galaxy at z=1.165. Analysis of the system determined the Einstein radius to be 2.16 arcseconds and the total enclosed mass producing the lensing effect to be 1.86 ± 0.23 × 1012 solar masses.
DISCOVERY OF A GALAXY CLUSTER WITH A VIOLENTLY STARBURSTING CORE AT z = 2:506Sérgio Sacani
We report the discovery of a remarkable concentration of massive galaxies with extended X-ray
emission at zspec = 2:506, which contains 11 massive (M & 1011M) galaxies in the central 80kpc
region (11.6 overdensity). We have spectroscopically conrmed 17 member galaxies with 11 from CO
and the remaining ones from H. The X-ray luminosity, stellar mass content and velocity dispersion
all point to a collapsed, cluster-sized dark matter halo with mass M200c = 1013:90:2M, making it
the most distant X-ray-detected cluster known to date. Unlike other clusters discovered so far, this
structure is dominated by star-forming galaxies (SFGs) in the core with only 2 out of the 11 massive
galaxies classied as quiescent. The star formation rate (SFR) in the 80kpc core reaches 3400 M
yr 1 with a gas depletion time of 200 Myr, suggesting that we caught this cluster in rapid build-up
of a dense core. The high SFR is driven by both a high abundance of SFGs and a higher starburst
fraction ( 25%, compared to 3%-5% in the eld). The presence of both a collapsed, cluster-sized
halo and a predominant population of massive SFGs suggests that this structure could represent an
important transition phase between protoclusters and mature clusters. It provides evidence that the
main phase of massive galaxy passivization will take place after galaxies accrete onto the cluster,
providing new insights into massive cluster formation at early epochs. The large integrated stellar
mass at such high redshift challenges our understanding of massive cluster formation.
A 2 4_determination_of_the_local_value_of_the_hubble_constantSérgio Sacani
We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to
reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%.
The bulk of this improvement comes from new, near-infrared observations of Cepheid
variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling
the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these
in turn leverage the magnitude-redshift relation based on 300 SNe Ia at z <0.15. All
19 hosts as well as the megamaser system NGC4258 have been observed with WFC3
in the optical and near-infrared, thus nullifying cross-instrument zeropoint errors in the
relative distance estimates from Cepheids. Other noteworthy improvements include a
33% reduction in the systematic uncertainty in the maser distance to NGC4258, a larger
sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to
the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of
Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW)
Cepheids.
SPECTROSCOPIC CONFIRMATION OF THE EXISTENCE OF LARGE, DIFFUSE GALAXIES IN THE...Sérgio Sacani
We recently identified a population of low surface brightness objects in the field of the z = 0.023 Coma cluster,
using the Dragonfly Telephoto Array. Here we present Keck spectroscopy of one of the largest of these “ultradiffuse
galaxies” (UDGs), confirming that it is a member of the cluster. The galaxy has prominent absorption
features, including the Ca II H+K lines and the G-band, and no detected emission lines. Its radial velocity of
cz=6280±120 km s−1 is within the 1σ velocity dispersion of the Coma cluster. The galaxy has an effective
radius of 4.3 ± 0.3 kpc and a Sérsic index of 0.89 ± 0.06, as measured from Keck imaging. We find no indications
of tidal tails or other distortions, at least out to a radius of ∼2re. We show that UDGs are located in a previously
sparsely populated region of the size—magnitude plane of quiescent stellar systems, as they are ∼6 mag fainter
than normal early-type galaxies of the same size. It appears that the luminosity distribution of large quiescent
galaxies is not continuous, although this could largely be due to selection effects. Dynamical measurements are
needed to determine whether the dark matter halos of UDGs are similar to those of galaxies with the same
luminosity or to those of galaxies with the same size.
First identification of_direct_collapse_black_holes_candidates_in_the_early_u...Sérgio Sacani
The first black hole seeds, formed when the Universe was younger than ⇠ 500Myr, are recognized
to play an important role for the growth of early (z ⇠ 7) super-massive black holes.
While progresses have been made in understanding their formation and growth, their observational
signatures remain largely unexplored. As a result, no detection of such sources has been
confirmed so far. Supported by numerical simulations, we present a novel photometric method
to identify black hole seed candidates in deep multi-wavelength surveys.We predict that these
highly-obscured sources are characterized by a steep spectrum in the infrared (1.6−4.5μm),
i.e. by very red colors. The method selects the only 2 objects with a robust X-ray detection
found in the CANDELS/GOODS-S survey with a photometric redshift z & 6. Fitting their
infrared spectra only with a stellar component would require unrealistic star formation rates
(& 2000M# yr−1). To date, the selected objects represent the most promising black hole seed
candidates, possibly formed via the direct collapse black hole scenario, with predicted mass
> 105M#. While this result is based on the best photometric observations of high-z sources
available to date, additional progress is expected from spectroscopic and deeper X-ray data.
Upcoming observatories, like the JWST, will greatly expand the scope of this work.
TEMPORAL EVOLUTION OF THE HIGH-ENERGY IRRADIATION AND WATER CONTENT OF TRAPPI...Sérgio Sacani
The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could
harbour liquid water on their surfaces. UV observations are essential to measure their high-energy
irradiation, and to search for photodissociated water escaping from their putative atmospheres. Our
new observations of TRAPPIST-1 Ly-α line during the transit of TRAPPIST-1c show an evolution of
the star emission over three months, preventing us from assessing the presence of an extended hydrogen
exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history
of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the
orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape.
However, TRAPPIST-1e to h might have lost less than 3 Earth oceans if hydrodynamic escape stopped
once they entered the habitable zone. We caution that these estimates remain limited by the large
uncertainty on the planet masses. They likely represent upper limits on the actual water loss because
our assumptions maximize the XUV-driven escape, while photodissociation in the upper atmospheres
should be the limiting process. Late-stage outgassing could also have contributed significant amounts
of water for the outer, more massive planets after they entered the habitable zone. While our results
suggest that the outer planets are the best candidates to search for water with the JWST, they also
highlight the need for theoretical studies and complementary observations in all wavelength domains
to determine the nature of the TRAPPIST-1 planets, and their potential habitability.
Keywords: planetary systems - Stars: individual: TRAPPIST-1
The Internal Structure of Asteroid (25143) Itokawa as Revealed by Detection o...WellingtonRodrigues2014
- The authors detected an acceleration in the rotation rate of asteroid (25143) Itokawa through photometric observations spanning 2001 to 2013.
- By measuring rotational phase offsets between observed and modeled lightcurves, they found a YORP acceleration of 3.54 ± 0.38 × 10−8 rad day−2, equivalent to a decrease in the asteroid's rotation period of about 45 ms per year.
- Thermophysical modeling of the detailed shape model from the Hayabusa spacecraft could not reconcile the observed YORP strength unless the asteroid's center of mass is shifted by about 21 m along its long axis. This suggests Itokawa has two components with different densities that merged, either from a
The completeness-corrected rate of stellar encounters with the Sun from the f...Sérgio Sacani
I report on close encounters of stars to the Sun found in the first Gaia data release (GDR1). Combining Gaia astrometry with radial
velocities of around 320 000 stars drawn from various catalogues, I integrate orbits in a Galactic potential to identify those stars which
come within a few parsecs. Such encounters could influence the solar system, for example through gravitational perturbations of the
Oort cloud. 16 stars are found to come within 2 pc (although a few of these have dubious data). This is fewer than were found in a
similar study based on Hipparcos data, even though the present study has many more candidates. This is partly because I reject stars
with large radial velocity uncertainties (>10 km s−1
), and partly because of missing stars in GDR1 (especially at the bright end). The
closest encounter found is Gl 710, a K dwarf long-known to come close to the Sun in about 1.3 Myr. The Gaia astrometry predict
a much closer passage than pre-Gaia estimates, however: just 16 000 AU (90% confidence interval: 10 000–21 000 AU), which will
bring this star well within the Oort cloud. Using a simple model for the spatial, velocity, and luminosity distributions of stars, together
with an approximation of the observational selection function, I model the incompleteness of this Gaia-based search as a function
of the time and distance of closest approach. Applying this to a subset of the observed encounters (excluding duplicates and stars
with implausibly large velocities), I estimate the rate of stellar encounters within 5 pc averaged over the past and future 5 Myr to be
545±59 Myr−1
. Assuming a quadratic scaling of the rate within some encounter distance (which my model predicts), this corresponds
to 87 ± 9 Myr−1 within 2 pc. A more accurate analysis and assessment will be possible with future Gaia data releases.
Detection of lyman_alpha_emission_from_a_triply_imaged_z_6_85_galaxy_behind_m...Sérgio Sacani
We report the detection of Ly emission at 9538A
in the Keck/DEIMOS and HST WFC3
G102 grism data from a triply-imaged galaxy at z = 6:846 0:001 behind galaxy cluster MACS
J2129.4 0741. Combining the emission line wavelength with broadband photometry, line ratio upper
limits, and lens modeling, we rule out the scenario that this emission line is [O II] at z = 1:57. After
accounting for magnication, we calculate the weighted average of the intrinsic Ly luminosity to be
1:31042 erg s 1 and Ly equivalent width to be 7415A. Its intrinsic UV absolute magnitude at
1600A
is 18:60:2 mag and stellar mass (1:50:3)107 M, making it one of the faintest (intrinsic
LUV 0:14 L
UV) galaxies with Ly detection at z 7 to date. Its stellar mass is in the typical range
for the galaxies thought to dominate the reionization photon budget at z & 7; the inferred Ly escape
fraction is high (& 10%), which could be common for sub-L z & 7 galaxies with Ly emission. This
galaxy oers a glimpse of the galaxy population that is thought to drive reionization, and it shows
that gravitational lensing is an important avenue to probe the sub-L galaxy population.
On some structural_features_of_the_metagalaxySérgio Sacani
Progress in a group of investigations designed
to discover some of the structural details in individual galaxies and in the
Metagalaxy is reported in the following pages.
(a) The first section is concerned with the distribution of cluster-type
Cepheids in high galactic latitude. To the 169 already known in latitudes,
greater than or equal to ± 20o
, the systematic variable star programme carried
on at Harvard has added 312, mostly fainter than magnitude 13-0. With
allowance for absorption and for uncertainties yet remaining in the mean
absolute magnitude of these stars, the thickness of the Milky Way, so far
as this type of star is concerned, is not less than twenty-five kiloparsecs ;
he extent of the Milky Way in its own plane, by the same criterion, is more
than thirty kiloparsecs, perhaps much more.
(b) The extent of the Milky Way in the anti-centre quadrant is considered
on the basis of classical and cluster-type Cepheids ; provisionally
it is found that the galactic system reaches to a distance of at least ten
kiloparsecs in longitude 150o
.
(r) More than six hundred new variables have been found in the Large
Magellanic Cloud and measured for position, ranges and median magnitudes ;
the frequency of periods is not unlike that for the classical Cepheids in the
galactic system ; the light curves also are comparable in all details. The
Magellanic Cepheids, like the galactic classical Cepheids, are concentrated
in regions of high star-density.
(d) Further study of the period-luminosity relation in the Large Magellanic
Cloud permits its revision and strengthening for the Cepheids of
highest absolute magnitude. An observed deviation from the relation
that had previously been found for the Small Cloud is probably to be
attributed to scale error in the magnitude system. No seriously disturbing
The ASTRODEEP Frontier Fields catalogues II. Photometric redshifts and rest f...Sérgio Sacani
This document describes a public release of photometric redshifts and galaxy properties from multi-wavelength data in the Abell-2744 and MACS-J0416 galaxy cluster fields observed as part of the Frontier Fields program. Photometric redshifts were estimated using six different methods and have an accuracy of 3-5%. Accounting for gravitational lensing magnification, the H-band number counts agree with CANDELS at bright magnitudes but extend to intrinsically fainter galaxies of H=32-33. The Frontier Fields data allow probing galaxy stellar masses 0.5-1.5 dex lower than in wide fields, including sources with masses of 107-108 solar masses at z>5. Star formation rates can be detected 1
Supermassive black holes in galaxy centres can grow by the accretion
of gas, liberating enormous amounts of energy that might
regulate star formation on galaxy-wide scales1–3
. The nature of
gaseous fuel reservoirs that power black hole growth is nevertheless
largely unconstrained by observations, and is instead routinely
simplified as a smooth, spherical inflow of very hot gas
in accordance with the Bondi solution4
. Recent theory5–7 and
simulations8–10 instead predict that accretion can be dominated by
a stochastic, clumpy distribution of very cold molecular clouds,
though unambiguous observational support for this prediction remains
elusive. Here we show observational evidence for a cold,
clumpy accretion flow toward a supermassive black hole fuel reservoir
in the nucleus of the Abell 2597 Brightest Cluster Galaxy
(BCG), a nearby (z = 0.0821) giant elliptical galaxy surrounded
by a dense halo of hot plasma11–13. Under the right conditions,
thermal instabilities can precipitate from this hot gas, producing a
rain of cold clouds that fall toward the galaxy’s centre14, sustaining
star formation amid a kiloparsec-scale molecular nebula that inhabits
its core15. New interferometric sub-millimetre observations
show that these cold clouds also fuel black hole accretion, revealing
“shadows” cast by molecular clouds as they move inward at ∼ 300
km s−1
toward the active supermassive black hole in the galaxy
centre, which serves as a bright backlight. Corroborating evidence
from prior observations16 of warmer atomic gas at extremely high
spatial resolution17, along with simple arguments based on geometry
and probability, indicates that these clouds are within the innermost
hundred parsecs of the black hole, and falling closer toward
it
This document summarizes research on determining temperatures, luminosities, and masses of the coldest known brown dwarfs. The key findings are:
1) Precise distances were measured for a sample of late-T and Y dwarfs using Spitzer Space Telescope astrometry, allowing accurate calculation of absolute fluxes, luminosities, and temperatures.
2) Y0 dwarfs were found to have temperatures of 400-450 K, significantly warmer than previous estimates, and masses of 5-20 times Jupiter's mass.
3) While having similar temperatures, Y dwarfs showed diverse spectral energy distributions, suggesting temperature alone does not determine spectra. Physical properties like gravity, clouds and chemistry also influence spectra.
Olivine in an_unexpected_location_on_vesta_surfaceSérgio Sacani
The document reports on the discovery of olivine on the surface of the asteroid Vesta in unexpected locations, based on data from the Dawn spacecraft's VIR instrument. Specifically:
- Olivine was found in the northern hemisphere of Vesta, rather than the southern basins where mantle rocks were expected based on previous models.
- The olivine occurs in large patches hundreds of meters across mixed with howardite regolith, unlike in meteorites where it is a minor component of diogenites.
- The amount and distribution of olivine-rich material suggests a complex evolutionary history for Vesta and is not consistent with previous ideas of olivine occurrence being associated with diogenites
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
WHERE IS THE FLUX GOING? THE LONG-TERM PHOTOMETRIC VARIABILITY OF BOYAJIAN’S ...Sérgio Sacani
We present ∼ 800 days of photometric monitoring of Boyajian’s Star (KIC 8462852) from the AllSky
Automated Survey for Supernovae (ASAS-SN) and ∼ 4000 days of monitoring from the All Sky
Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian’s Star
has steadily decreased at a rate of 6.3 ± 1.4 mmag yr−1
, such that the star is now 1.5% fainter than it
was in February 2015. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian’s
Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a
monotonic decline. We analyze a sample of ∼ 1000 comparison stars of similar brightness located in
the same ASAS-SN field and demonstrate that the recent fading is significant at & 99.4% confidence.
The 2015 − 2017 dimming rate is consistent with that measured with Kepler data for the time period
from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models
for the star’s behavior proposed to date
Proper-motion age dating of the progeny of Nova Scorpii ad 1437Sérgio Sacani
‘Cataclysmic variables’ are binary star systems in which one
star of the pair is a white dwarf, and which often generate bright
and energetic stellar outbursts. Classical novae are one type of
outburst: when the white dwarf accretes enough matter from its
companion, the resulting hydrogen-rich atmospheric envelope
can host a runaway thermonuclear reaction that generates a rapid
brightening1–4. Achieving peak luminosities of up to one million
times that of the Sun5
, all classical novae are recurrent, on timescales
of months6
to millennia7
. During the century before and after an
eruption, the ‘novalike’ binary systems that give rise to classical
novae exhibit high rates of mass transfer to their white dwarfs8
.
Another type of outburst is the dwarf nova: these occur in binaries
that have stellar masses and periods indistinguishable from those
of novalikes9
but much lower mass-transfer rates10, when accretiondisk
instabilities11 drop matter onto the white dwarfs. The coexistence
at the same orbital period of novalike binaries and dwarf
novae—which are identical but for their widely varying accretion
rates—has been a longstanding puzzle9
. Here we report the recovery
of the binary star underlying the classical nova eruption of 11 March
ad 1437 (refs 12, 13), and independently confirm its age by propermotion
dating. We show that, almost 500 years after a classical-nova
event, the system exhibited dwarf-nova eruptions. The three other
oldest recovered classical novae14–16 display nova shells, but lack
firm post-eruption ages17,18, and are also dwarf novae at present.
We conclude that many old novae become dwarf novae for part of
the millennia between successive nova eruptions19,
Artigo descreve como os cientistas utilizaram o Telescópio Espacial Hubble para descobrir a estratosfera num exoplaneta classificado como um Júpiter quente. Descoberta essa que pode ajudar a descobrir como os exoplanetas se formam e qual a composição de suas atmosferas.
We present deep optical images of the Large and Small Magellanic Clouds (LMC and SMC) using
a low cost telephoto lens with a wide field of view to explore stellar substructure in the outskirts
of the stellar disk of the LMC (r < 10 degrees from the center). These data have higher resolution
than existing star count maps, and highlight the existence of stellar arcs and multiple spiral arms in
the northern periphery, with no comparable counterparts in the South. We compare these data to
detailed simulations of the LMC disk outskirts, following interactions with its low mass companion,
the SMC. We consider interaction in isolation and with the inclusion of the Milky Way tidal field.
The simulations are used to assess the origin of the northern structures, including also the low density
stellar arc recently identified in the DES data by Mackey et al. (2015) at ∼ 15 degrees. We conclude
that repeated close interactions with the SMC are primarily responsible for the asymmetric stellar
structures seen in the periphery of the LMC. The orientation and density of these arcs can be used to
constrain the LMC’s interaction history with and impact parameter of the SMC. More generally, we
find that such asymmetric structures should be ubiquitous about pairs of dwarfs and can persist for
1-2 Gyr even after the secondary merges entirely with the primary. As such, the lack of a companion
around a Magellanic Irregular does not disprove the hypothesis that their asymmetric structures are
driven by dwarf-dwarf interactions.
Detection of solar_like_oscillations_in_relies_of_the_milk_way_asteroseismolo...Sérgio Sacani
Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens
of thousands of field stars. Tests against independent estimates of these properties are however
scarce, especially in the metal-poor regime. Here, we report the detection of solar-like
oscillations in 8 stars belonging to the red-giant branch and red-horizontal branch of the globular
cluster M4. The detections were made in photometric observations from the K2 Mission
during its Campaign 2. Making use of independent constraints on the distance, we estimate
masses of the 8 stars by utilising different combinations of seismic and non-seismic inputs.
When introducing a correction to the Δν scaling relation as suggested by stellar models, for
RGB stars we find excellent agreement with the expected masses from isochrone fitting, and
with a distance modulus derived using independent methods. The offset with respect to independent
masses is lower, or comparable with, the uncertainties on the average RGB mass
(4 − 10%, depending on the combination of constraints used). Our results lend confidence to
asteroseismic masses in the metal poor regime. We note that a larger sample will be needed
to allow more stringent tests to be made of systematic uncertainties in all the observables
(both seismic and non-seismic), and to explore the properties of RHB stars, and of different
populations in the cluster.
The document summarizes the discovery of transient bright features detected in Titan's northern sea, Ligeia Mare, by the Cassini spacecraft's radar instrument in July 2013. These features were not seen in previous or subsequent observations. The author analyzes potential explanations and argues that the features were likely ephemeral phenomena caused by surface waves, bubbles, or suspended solids. This suggests dynamic processes are starting in Titan's northern lakes and seas as summer approaches in the northern hemisphere.
The canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
This document reports the discovery of a newly discovered optical Einstein ring (ER) called the "Canarias Einstein Ring". It was discovered serendipitously in imaging data from the Dark Energy Camera. Follow-up spectroscopy with the Gran Telescopio CANARIAS confirmed the nature of the system, with the lens being an early-type galaxy at a redshift of z=0.581 and the source being a starburst galaxy at z=1.165. Analysis of the system determined the Einstein radius to be 2.16 arcseconds and the total enclosed mass producing the lensing effect to be 1.86 ± 0.23 × 1012 solar masses.
DISCOVERY OF A GALAXY CLUSTER WITH A VIOLENTLY STARBURSTING CORE AT z = 2:506Sérgio Sacani
We report the discovery of a remarkable concentration of massive galaxies with extended X-ray
emission at zspec = 2:506, which contains 11 massive (M & 1011M) galaxies in the central 80kpc
region (11.6 overdensity). We have spectroscopically conrmed 17 member galaxies with 11 from CO
and the remaining ones from H. The X-ray luminosity, stellar mass content and velocity dispersion
all point to a collapsed, cluster-sized dark matter halo with mass M200c = 1013:90:2M, making it
the most distant X-ray-detected cluster known to date. Unlike other clusters discovered so far, this
structure is dominated by star-forming galaxies (SFGs) in the core with only 2 out of the 11 massive
galaxies classied as quiescent. The star formation rate (SFR) in the 80kpc core reaches 3400 M
yr 1 with a gas depletion time of 200 Myr, suggesting that we caught this cluster in rapid build-up
of a dense core. The high SFR is driven by both a high abundance of SFGs and a higher starburst
fraction ( 25%, compared to 3%-5% in the eld). The presence of both a collapsed, cluster-sized
halo and a predominant population of massive SFGs suggests that this structure could represent an
important transition phase between protoclusters and mature clusters. It provides evidence that the
main phase of massive galaxy passivization will take place after galaxies accrete onto the cluster,
providing new insights into massive cluster formation at early epochs. The large integrated stellar
mass at such high redshift challenges our understanding of massive cluster formation.
A 2 4_determination_of_the_local_value_of_the_hubble_constantSérgio Sacani
We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to
reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%.
The bulk of this improvement comes from new, near-infrared observations of Cepheid
variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling
the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these
in turn leverage the magnitude-redshift relation based on 300 SNe Ia at z <0.15. All
19 hosts as well as the megamaser system NGC4258 have been observed with WFC3
in the optical and near-infrared, thus nullifying cross-instrument zeropoint errors in the
relative distance estimates from Cepheids. Other noteworthy improvements include a
33% reduction in the systematic uncertainty in the maser distance to NGC4258, a larger
sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to
the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of
Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW)
Cepheids.
SPECTROSCOPIC CONFIRMATION OF THE EXISTENCE OF LARGE, DIFFUSE GALAXIES IN THE...Sérgio Sacani
We recently identified a population of low surface brightness objects in the field of the z = 0.023 Coma cluster,
using the Dragonfly Telephoto Array. Here we present Keck spectroscopy of one of the largest of these “ultradiffuse
galaxies” (UDGs), confirming that it is a member of the cluster. The galaxy has prominent absorption
features, including the Ca II H+K lines and the G-band, and no detected emission lines. Its radial velocity of
cz=6280±120 km s−1 is within the 1σ velocity dispersion of the Coma cluster. The galaxy has an effective
radius of 4.3 ± 0.3 kpc and a Sérsic index of 0.89 ± 0.06, as measured from Keck imaging. We find no indications
of tidal tails or other distortions, at least out to a radius of ∼2re. We show that UDGs are located in a previously
sparsely populated region of the size—magnitude plane of quiescent stellar systems, as they are ∼6 mag fainter
than normal early-type galaxies of the same size. It appears that the luminosity distribution of large quiescent
galaxies is not continuous, although this could largely be due to selection effects. Dynamical measurements are
needed to determine whether the dark matter halos of UDGs are similar to those of galaxies with the same
luminosity or to those of galaxies with the same size.
First identification of_direct_collapse_black_holes_candidates_in_the_early_u...Sérgio Sacani
The first black hole seeds, formed when the Universe was younger than ⇠ 500Myr, are recognized
to play an important role for the growth of early (z ⇠ 7) super-massive black holes.
While progresses have been made in understanding their formation and growth, their observational
signatures remain largely unexplored. As a result, no detection of such sources has been
confirmed so far. Supported by numerical simulations, we present a novel photometric method
to identify black hole seed candidates in deep multi-wavelength surveys.We predict that these
highly-obscured sources are characterized by a steep spectrum in the infrared (1.6−4.5μm),
i.e. by very red colors. The method selects the only 2 objects with a robust X-ray detection
found in the CANDELS/GOODS-S survey with a photometric redshift z & 6. Fitting their
infrared spectra only with a stellar component would require unrealistic star formation rates
(& 2000M# yr−1). To date, the selected objects represent the most promising black hole seed
candidates, possibly formed via the direct collapse black hole scenario, with predicted mass
> 105M#. While this result is based on the best photometric observations of high-z sources
available to date, additional progress is expected from spectroscopic and deeper X-ray data.
Upcoming observatories, like the JWST, will greatly expand the scope of this work.
TEMPORAL EVOLUTION OF THE HIGH-ENERGY IRRADIATION AND WATER CONTENT OF TRAPPI...Sérgio Sacani
The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could
harbour liquid water on their surfaces. UV observations are essential to measure their high-energy
irradiation, and to search for photodissociated water escaping from their putative atmospheres. Our
new observations of TRAPPIST-1 Ly-α line during the transit of TRAPPIST-1c show an evolution of
the star emission over three months, preventing us from assessing the presence of an extended hydrogen
exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history
of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the
orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape.
However, TRAPPIST-1e to h might have lost less than 3 Earth oceans if hydrodynamic escape stopped
once they entered the habitable zone. We caution that these estimates remain limited by the large
uncertainty on the planet masses. They likely represent upper limits on the actual water loss because
our assumptions maximize the XUV-driven escape, while photodissociation in the upper atmospheres
should be the limiting process. Late-stage outgassing could also have contributed significant amounts
of water for the outer, more massive planets after they entered the habitable zone. While our results
suggest that the outer planets are the best candidates to search for water with the JWST, they also
highlight the need for theoretical studies and complementary observations in all wavelength domains
to determine the nature of the TRAPPIST-1 planets, and their potential habitability.
Keywords: planetary systems - Stars: individual: TRAPPIST-1
The Internal Structure of Asteroid (25143) Itokawa as Revealed by Detection o...WellingtonRodrigues2014
- The authors detected an acceleration in the rotation rate of asteroid (25143) Itokawa through photometric observations spanning 2001 to 2013.
- By measuring rotational phase offsets between observed and modeled lightcurves, they found a YORP acceleration of 3.54 ± 0.38 × 10−8 rad day−2, equivalent to a decrease in the asteroid's rotation period of about 45 ms per year.
- Thermophysical modeling of the detailed shape model from the Hayabusa spacecraft could not reconcile the observed YORP strength unless the asteroid's center of mass is shifted by about 21 m along its long axis. This suggests Itokawa has two components with different densities that merged, either from a
The completeness-corrected rate of stellar encounters with the Sun from the f...Sérgio Sacani
I report on close encounters of stars to the Sun found in the first Gaia data release (GDR1). Combining Gaia astrometry with radial
velocities of around 320 000 stars drawn from various catalogues, I integrate orbits in a Galactic potential to identify those stars which
come within a few parsecs. Such encounters could influence the solar system, for example through gravitational perturbations of the
Oort cloud. 16 stars are found to come within 2 pc (although a few of these have dubious data). This is fewer than were found in a
similar study based on Hipparcos data, even though the present study has many more candidates. This is partly because I reject stars
with large radial velocity uncertainties (>10 km s−1
), and partly because of missing stars in GDR1 (especially at the bright end). The
closest encounter found is Gl 710, a K dwarf long-known to come close to the Sun in about 1.3 Myr. The Gaia astrometry predict
a much closer passage than pre-Gaia estimates, however: just 16 000 AU (90% confidence interval: 10 000–21 000 AU), which will
bring this star well within the Oort cloud. Using a simple model for the spatial, velocity, and luminosity distributions of stars, together
with an approximation of the observational selection function, I model the incompleteness of this Gaia-based search as a function
of the time and distance of closest approach. Applying this to a subset of the observed encounters (excluding duplicates and stars
with implausibly large velocities), I estimate the rate of stellar encounters within 5 pc averaged over the past and future 5 Myr to be
545±59 Myr−1
. Assuming a quadratic scaling of the rate within some encounter distance (which my model predicts), this corresponds
to 87 ± 9 Myr−1 within 2 pc. A more accurate analysis and assessment will be possible with future Gaia data releases.
Detection of lyman_alpha_emission_from_a_triply_imaged_z_6_85_galaxy_behind_m...Sérgio Sacani
We report the detection of Ly emission at 9538A
in the Keck/DEIMOS and HST WFC3
G102 grism data from a triply-imaged galaxy at z = 6:846 0:001 behind galaxy cluster MACS
J2129.4 0741. Combining the emission line wavelength with broadband photometry, line ratio upper
limits, and lens modeling, we rule out the scenario that this emission line is [O II] at z = 1:57. After
accounting for magnication, we calculate the weighted average of the intrinsic Ly luminosity to be
1:31042 erg s 1 and Ly equivalent width to be 7415A. Its intrinsic UV absolute magnitude at
1600A
is 18:60:2 mag and stellar mass (1:50:3)107 M, making it one of the faintest (intrinsic
LUV 0:14 L
UV) galaxies with Ly detection at z 7 to date. Its stellar mass is in the typical range
for the galaxies thought to dominate the reionization photon budget at z & 7; the inferred Ly escape
fraction is high (& 10%), which could be common for sub-L z & 7 galaxies with Ly emission. This
galaxy oers a glimpse of the galaxy population that is thought to drive reionization, and it shows
that gravitational lensing is an important avenue to probe the sub-L galaxy population.
On some structural_features_of_the_metagalaxySérgio Sacani
Progress in a group of investigations designed
to discover some of the structural details in individual galaxies and in the
Metagalaxy is reported in the following pages.
(a) The first section is concerned with the distribution of cluster-type
Cepheids in high galactic latitude. To the 169 already known in latitudes,
greater than or equal to ± 20o
, the systematic variable star programme carried
on at Harvard has added 312, mostly fainter than magnitude 13-0. With
allowance for absorption and for uncertainties yet remaining in the mean
absolute magnitude of these stars, the thickness of the Milky Way, so far
as this type of star is concerned, is not less than twenty-five kiloparsecs ;
he extent of the Milky Way in its own plane, by the same criterion, is more
than thirty kiloparsecs, perhaps much more.
(b) The extent of the Milky Way in the anti-centre quadrant is considered
on the basis of classical and cluster-type Cepheids ; provisionally
it is found that the galactic system reaches to a distance of at least ten
kiloparsecs in longitude 150o
.
(r) More than six hundred new variables have been found in the Large
Magellanic Cloud and measured for position, ranges and median magnitudes ;
the frequency of periods is not unlike that for the classical Cepheids in the
galactic system ; the light curves also are comparable in all details. The
Magellanic Cepheids, like the galactic classical Cepheids, are concentrated
in regions of high star-density.
(d) Further study of the period-luminosity relation in the Large Magellanic
Cloud permits its revision and strengthening for the Cepheids of
highest absolute magnitude. An observed deviation from the relation
that had previously been found for the Small Cloud is probably to be
attributed to scale error in the magnitude system. No seriously disturbing
The ASTRODEEP Frontier Fields catalogues II. Photometric redshifts and rest f...Sérgio Sacani
This document describes a public release of photometric redshifts and galaxy properties from multi-wavelength data in the Abell-2744 and MACS-J0416 galaxy cluster fields observed as part of the Frontier Fields program. Photometric redshifts were estimated using six different methods and have an accuracy of 3-5%. Accounting for gravitational lensing magnification, the H-band number counts agree with CANDELS at bright magnitudes but extend to intrinsically fainter galaxies of H=32-33. The Frontier Fields data allow probing galaxy stellar masses 0.5-1.5 dex lower than in wide fields, including sources with masses of 107-108 solar masses at z>5. Star formation rates can be detected 1
Supermassive black holes in galaxy centres can grow by the accretion
of gas, liberating enormous amounts of energy that might
regulate star formation on galaxy-wide scales1–3
. The nature of
gaseous fuel reservoirs that power black hole growth is nevertheless
largely unconstrained by observations, and is instead routinely
simplified as a smooth, spherical inflow of very hot gas
in accordance with the Bondi solution4
. Recent theory5–7 and
simulations8–10 instead predict that accretion can be dominated by
a stochastic, clumpy distribution of very cold molecular clouds,
though unambiguous observational support for this prediction remains
elusive. Here we show observational evidence for a cold,
clumpy accretion flow toward a supermassive black hole fuel reservoir
in the nucleus of the Abell 2597 Brightest Cluster Galaxy
(BCG), a nearby (z = 0.0821) giant elliptical galaxy surrounded
by a dense halo of hot plasma11–13. Under the right conditions,
thermal instabilities can precipitate from this hot gas, producing a
rain of cold clouds that fall toward the galaxy’s centre14, sustaining
star formation amid a kiloparsec-scale molecular nebula that inhabits
its core15. New interferometric sub-millimetre observations
show that these cold clouds also fuel black hole accretion, revealing
“shadows” cast by molecular clouds as they move inward at ∼ 300
km s−1
toward the active supermassive black hole in the galaxy
centre, which serves as a bright backlight. Corroborating evidence
from prior observations16 of warmer atomic gas at extremely high
spatial resolution17, along with simple arguments based on geometry
and probability, indicates that these clouds are within the innermost
hundred parsecs of the black hole, and falling closer toward
it
This document summarizes research on determining temperatures, luminosities, and masses of the coldest known brown dwarfs. The key findings are:
1) Precise distances were measured for a sample of late-T and Y dwarfs using Spitzer Space Telescope astrometry, allowing accurate calculation of absolute fluxes, luminosities, and temperatures.
2) Y0 dwarfs were found to have temperatures of 400-450 K, significantly warmer than previous estimates, and masses of 5-20 times Jupiter's mass.
3) While having similar temperatures, Y dwarfs showed diverse spectral energy distributions, suggesting temperature alone does not determine spectra. Physical properties like gravity, clouds and chemistry also influence spectra.
Olivine in an_unexpected_location_on_vesta_surfaceSérgio Sacani
The document reports on the discovery of olivine on the surface of the asteroid Vesta in unexpected locations, based on data from the Dawn spacecraft's VIR instrument. Specifically:
- Olivine was found in the northern hemisphere of Vesta, rather than the southern basins where mantle rocks were expected based on previous models.
- The olivine occurs in large patches hundreds of meters across mixed with howardite regolith, unlike in meteorites where it is a minor component of diogenites.
- The amount and distribution of olivine-rich material suggests a complex evolutionary history for Vesta and is not consistent with previous ideas of olivine occurrence being associated with diogenites
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
WHERE IS THE FLUX GOING? THE LONG-TERM PHOTOMETRIC VARIABILITY OF BOYAJIAN’S ...Sérgio Sacani
We present ∼ 800 days of photometric monitoring of Boyajian’s Star (KIC 8462852) from the AllSky
Automated Survey for Supernovae (ASAS-SN) and ∼ 4000 days of monitoring from the All Sky
Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian’s Star
has steadily decreased at a rate of 6.3 ± 1.4 mmag yr−1
, such that the star is now 1.5% fainter than it
was in February 2015. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian’s
Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a
monotonic decline. We analyze a sample of ∼ 1000 comparison stars of similar brightness located in
the same ASAS-SN field and demonstrate that the recent fading is significant at & 99.4% confidence.
The 2015 − 2017 dimming rate is consistent with that measured with Kepler data for the time period
from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models
for the star’s behavior proposed to date
Proper-motion age dating of the progeny of Nova Scorpii ad 1437Sérgio Sacani
‘Cataclysmic variables’ are binary star systems in which one
star of the pair is a white dwarf, and which often generate bright
and energetic stellar outbursts. Classical novae are one type of
outburst: when the white dwarf accretes enough matter from its
companion, the resulting hydrogen-rich atmospheric envelope
can host a runaway thermonuclear reaction that generates a rapid
brightening1–4. Achieving peak luminosities of up to one million
times that of the Sun5
, all classical novae are recurrent, on timescales
of months6
to millennia7
. During the century before and after an
eruption, the ‘novalike’ binary systems that give rise to classical
novae exhibit high rates of mass transfer to their white dwarfs8
.
Another type of outburst is the dwarf nova: these occur in binaries
that have stellar masses and periods indistinguishable from those
of novalikes9
but much lower mass-transfer rates10, when accretiondisk
instabilities11 drop matter onto the white dwarfs. The coexistence
at the same orbital period of novalike binaries and dwarf
novae—which are identical but for their widely varying accretion
rates—has been a longstanding puzzle9
. Here we report the recovery
of the binary star underlying the classical nova eruption of 11 March
ad 1437 (refs 12, 13), and independently confirm its age by propermotion
dating. We show that, almost 500 years after a classical-nova
event, the system exhibited dwarf-nova eruptions. The three other
oldest recovered classical novae14–16 display nova shells, but lack
firm post-eruption ages17,18, and are also dwarf novae at present.
We conclude that many old novae become dwarf novae for part of
the millennia between successive nova eruptions19,
Artigo descreve como os cientistas utilizaram o Telescópio Espacial Hubble para descobrir a estratosfera num exoplaneta classificado como um Júpiter quente. Descoberta essa que pode ajudar a descobrir como os exoplanetas se formam e qual a composição de suas atmosferas.
First detection of CO2 emission in a Centaur: JWST NIRSpec observations of 39...Sérgio Sacani
Centaurs are minor solar system bodies with orbits transitioning between those of Trans-Neptunian
Scattered Disk objects and Jupiter Family comets. 39P/Oterma is a frequently active Centaur that
has recently held both Centaur and JFC classifications and was observed with the JWST NIRSpec
instrument on 2022 July 27 UTC while it was 5.82 au from the Sun. For the first time, CO2 gas
emission was detected in a Centaur, with a production rate of QCO2 = (5.96 ± 0.80) × 1023 molecules
s
−1
. This is the lowest detection of CO2 of any Centaur or comet. CO and H2O were not detected
down to constraining upper limits. Derived mixing ratios of QCO/QCO2 ≤2.03 and QCO2
/QH2O ≥0.60
are consistent with CO2 and/or CO outgassing playing large roles in driving the activity, but not water,
and show a significant difference between the coma abundances of 29P/Schwassmann-Wachmann 1,
another Centaur at a similar heliocentric distance, which may be explained by thermal processing of
39P’s surface during its previous Jupiter-family comet orbit. To help contextualize the JWST data we
also acquired visible CCD imaging data on two dates in July (Gemini North) and September (Lowell
Discovery Telescope) 2022. Image analysis and photometry based on these data are consistent with a
point source detection and an estimated effective nucleus radius of 39P in the range of Rnuc =2.21 to
2.49 km.
A precise water_abundance_measurement_for_the_hot_jupiter_wasp_43bSérgio Sacani
This document presents a precise measurement of the water abundance in the atmosphere of the exoplanet WASP-43b using transmission and thermal emission spectroscopy from the Hubble Space Telescope. The key findings are:
1) The water content of WASP-43b's atmosphere is consistent with solar composition at planetary temperatures, ranging from 0.4 to 3.5 times the solar water abundance.
2) This metallicity measurement extends the trend seen in the solar system of lower metal enrichment for higher mass planets.
3) Measuring a planet's water content constrains its formation location in the protoplanetary disk and provides insight into planetary formation models.
Is the atmosphere of the ultra-hot Jupiter WASP-121 b variable?Sérgio Sacani
We present a comprehensive analysis of the Hubble Space Telescope observations of the atmosphere
of WASP-121 b, a ultra-hot Jupiter. After reducing the transit, eclipse, and phase-curve observations
with a uniform methodology and addressing the biases from instrument systematics, sophisticated
atmospheric retrievals are used to extract robust constraints on the thermal structure, chemistry, and
cloud properties of the atmosphere. Our analysis shows that the observations are consistent with a
strong thermal inversion beginning at ∼104 Pa on the dayside, solar to subsolar metallicity Z (i.e.,
−0.77 < log(Z) < 0.05), and super-solar C/O ratio (i.e., 0.59 < C/O < 0.87). More importantly,
utilizing the high signal-to-noise ratio and repeated observations of the planet, we identify the following
unambiguous time-varying signals in the data: i) a shift of the putative hotspot offset between the
two phase-curves and ii) varying spectral signatures in the transits and eclipses. By simulating the
global dynamics of WASP-121 b atmosphere at high-resolution, we show that the identified signals are
consistent with quasi-periodic weather patterns, hence atmospheric variability, with signatures at the
level probed by the observations (∼5% to ∼10%) that change on a timescale of ∼5 planet days; in
the simulations, the weather patterns arise from the formation and movement of storms and fronts,
causing hot (as well as cold) patches of atmosphere to deform, separate, and mix in time.
This document summarizes the results of infrared transmission spectroscopy of the exoplanets HD 209458b and XO-1b using the Hubble Space Telescope's Wide Field Camera 3 instrument. Key findings include:
- Both planets exhibited water absorption of approximately 200 ppm at the peak water absorption wavelength of 1.38 microns.
- The water absorption measured for XO-1b contradicts stronger absorption reported from previous observations using a different instrument.
- The weak water absorption measured for HD 209458b is consistent with previous observations of weak molecular absorption features for this planet.
- Model atmospheres including uniformly distributed extra opacity can approximately account for the water measurements as well as previous sodium absorption measurements for
Spirals and clumps in V960 Mon: signs of planet formation via gravitational i...Sérgio Sacani
The formation of giant planets has traditionally been divided into two pathways: core accretion and gravitational instability. However, in recent years, gravitational instability has become less favored, primarily due
to the scarcity of observations of fragmented protoplanetary disks around young stars and low occurrence rate
of massive planets on very wide orbits. In this study, we present a SPHERE/IRDIS polarized light observation
of the young outbursting object V960 Mon. The image reveals a vast structure of intricately shaped scattered
light with several spiral arms. This finding motivated a re-analysis of archival ALMA 1.3 mm data acquired
just two years after the onset of the outburst of V960 Mon. In these data, we discover several clumps of continuum emission aligned along a spiral arm that coincides with the scattered light structure. We interpret the
localized emission as fragments formed from a spiral arm under gravitational collapse. Estimating the mass of
solids within these clumps to be of several Earth masses, we suggest this observation to be the first evidence of
gravitational instability occurring on planetary scales. This study discusses the significance of this finding for
planet formation and its potential connection with the outbursting state of V960 Mon.
A continuum from_clear_to_cloudy_hot_jupiter_exoplanets_without_primordial_wa...Sérgio Sacani
Uma pesquisa de 10 exoplanetas quentes, do tamanho de Júpiter, conduzida com os telescópios Spitzer e Hubble da NASA levou uma equipe de astrônomos a resolverem um mistério que já durava algum tempo – por que alguns desses mundos têm menos água do que o esperado? A descoberta, oferece novas ideias sobre uma vasta coleção de atmosferas planetárias na nossa galáxia e sobre como os planetas são formados.
Dos quase 2000 planetas confirmados orbitando outras estrelas, um subconjunto deles são planetas gasosos com características similares ao planeta Júpiter, mas, como suas órbitas são muito próximas de suas estrelas, eles são terrivelmente quentes.
A proximidade desses exoplanetas das suas estrelas, faz com que seja difícil observá-los. Devido a essa dificuldade, o Hubble só conseguiu explorar poucos desses exoplanetas, chamados de Júpiteres Quentes, no passado. Esses estudos iniciais descobriram que alguns planetas possuem menos água do que era previsto pelos modelos atmosféricos.
Uma equipe internacional de astrônomos tem atacado o problema fazendo o maior catálogo espectroscópico de atmosferas de exoplanetas até o momento. Todos os planetas no catálogo seguem órbitas orientadas de modo que o planeta passa em frente da estrela quando visto da Terra. Devido a esse trânsito, parte da luz da estrela viaja pela atmosfera externa do exoplaneta. “A atmosfera deixa sua impressão digital única na luz da estrela, que nós podemos estudar, quando ela chega até nós”, explicou a coautora Hannah Wakeford, do Goddard Space Flight Center da NASA , em Greenbelt, Maryland.
Kinematics and simulations_of_the_stellar_stream_in_the_halo_of_the_umbrella_...Sérgio Sacani
This document summarizes a study of the stellar stream and substructures around the Umbrella Galaxy (NGC 4651). Deep imaging and spectroscopy were used to characterize the properties and kinematics of the stream. Tracer objects like globular clusters and planetary nebulae were identified and found to delineate a kinematically cold feature in position-velocity space. Dynamical modeling suggests the stream originated from the tidal disruption of a dwarf galaxy on a highly eccentric orbit about 6-10 billion years ago. This work demonstrates the feasibility of using discrete tracers to recover the kinematics and model the dynamics of low surface brightness stellar streams around distant galaxies.
T he effect_of_orbital_configuration)_on_the_possible_climates_and_habitabili...Sérgio Sacani
This research article explores how the orbital configuration of Kepler-62f, a potentially habitable exoplanet in a five-planet system, could affect its climate and habitability. N-body simulations were used to determine the stable range of orbital eccentricities for Kepler-62f. Climate simulations using two global climate models then examined the planet's surface habitability across this range of eccentricities and for different atmospheric compositions. The simulations found multiple combinations of orbital and atmospheric parameters that could allow for surface liquid water on Kepler-62f, including higher orbital eccentricities coupled with high planetary obliquity or atmospheric CO2 levels above 3 bars.
First results from_the_hubble_opal_program_jupiter_in_2015Sérgio Sacani
Os cientistas usando o Telescópio Espacial Hubble da NASA/ESA produziram novos mapas de Júpiter, que mostram as contínuas mudanças que ocorrem com a famosa Grande Mancha Vermelha. As imagens também revelam uma rara estrutura em forma de onda na atmosfera do planeta que não tinha sido vista por décadas. A nova imagem é a primeira de uma série de retratos anuais dos planetas externos do Sistema Solar, que nos darão um novo olhar desses mundos remotos, e ajudarão os cientistas a estudarem como eles mudam com o passar do tempo.
Nessa nova imagem de Júpiter, uma grande quantidade de feições foi capturada incluindo ventos, nuvens e tempestades. Os cientistas por trás dessas novas imagens, as obtiveram usando a Wide Field Camera 3 do Hubble, num período de observação de mais de 10 horas e produziram assim dois mapas completos do planeta, a partir das suas observações. Esses mapas fizeram com que fosse possível determinar a velocidade dos ventos em Júpiter, com a finalidade de identificar diferentes fenômenos na sua atmosfera além de traquear as suas feições mais famosas.
As novas imagens confirmam que a grande tempestade que tem existido na superfície de nuvens de Júpiter por no mínimo 300 anos, continua a encolher, mas mesmo que desapareça, ela irá morrer lutando. A tempestade, conhecida como Grande Mancha Vermelha, é vista aqui fazendo seus movimentos em espiral no centro da imagem do planeta. Ela tem diminuído de tamanho de maneira muito rápida de ano em ano. Mas agora, a taxa de encolhimento parece ter reduzido novamente, mesmo apesar da mancha ser cerca de 240 quilômetros menor do que era em 2014.
Evidence for a_complex_enrichment_history_of_the_stream_from_fairall_9_sightlineSérgio Sacani
This study analyzes absorption spectra of the Magellanic Stream (MS) toward the quasar Fairall 9, obtained using the Hubble Space Telescope Cosmic Origins Spectrograph (HST/COS) and the Very Large Telescope Ultraviolet and Visible Echelle Spectrograph (VLT/UVES). The spectra reveal absorption from multiple velocity components of the MS, indicating multiphase gas. Surprisingly, the sulfur abundance is found to be high ([S/H] = -0.30), five times higher than other MS sightlines, while the nitrogen abundance is lower ([N/H] = -1.15). This points to a complex enrichment history, where the gas toward Fair
A Tale of 3 Dwarf Planets: Ices and Organics on Sedna, Gonggong, and Quaoar f...Sérgio Sacani
The dwarf planets Sedna, Gonggong, and Quaoar are interesting in being somewhat smaller than
the methane-rich bodies of the Kuiper Belt (Pluto, Eris, Makemake), yet large enough to be
spherical and to have possibly undergone interior melting and differentiation. They also reside
on very different orbits, making them an ideal suite of bodies for untangling effects of size and
orbit on present day surface composition. We observed Sedna, Gonggong, and Quaoar with the
NIRSpec instrument on the James Webb Space Telescope (JWST). All three bodies were
observed in the low-resolution prism mode at wavelengths spanning 0.7 to 5.2 μm. Quaoar was
additionally observed at 10x higher spectral resolution from 0.97 to 3.16 μm using mediumresolution gratings. Sedna’s spectrum shows a large number of absorption features due to ethane
(C2H6), as well as acetylene (C2H2), ethylene (C2H4), H2O, and possibly minor CO2.
Gonggong’s spectrum also shows several, but fewer and weaker, ethane features, along with
stronger and cleaner H2O features and CO2 complexed with other molecules. Quaoar’s prism
spectrum shows even fewer and weaker ethane features, the deepest and cleanest H2O features, a
feature at 3.2 μm possibly due to HCN, and CO2 ice. The higher-resolution medium grating
spectrum of Quaoar reveals several overtone and combination bands of ethane and methane
(CH4). Spectra of all three objects show steep red spectral slopes and strong, broad absorptions
between 2.7 and 3.6 μm indicative of complex organic molecules. The suite of light
hydrocarbons and complex organic molecules are interpreted as the products of irradiation of
methane. The differences in apparent abundances of irradiation products among these three
similarly-sized bodies are likely due to their distinctive orbits, which lead to different timescales
of methane retention and to different charged particle irradiation environments. In all cases,
however, the continued presence of light hydrocarbons implies a resupply of methane to the
2
surface. We suggest that these three bodies have undergone internal melting and geochemical
evolution similar to the larger dwarf planets and distinct from all smaller KBOs. The feature
identification presented in this paper is the first step of analysis, and additional insight into the
relative abundances and mixing states of materials on these surfaces will come from future
spectral modeling of these data.
SO and SiS Emission Tracing an Embedded Planet and Compact 12CO and 13CO Coun...Sérgio Sacani
Planets form in dusty, gas-rich disks around young stars, while at the same time, the planet formation
process alters the physical and chemical structure of the disk itself. Embedded planets will locally heat
the disk and sublimate volatile-rich ices, or in extreme cases, result in shocks that sputter heavy atoms
such as Si from dust grains. This should cause chemical asymmetries detectable in molecular gas
observations. Using high-angular-resolution ALMA archival data of the HD 169142 disk, we identify
compact SO J=88–77 and SiS J=19–18 emission coincident with the position of a ∼2 MJup planet seen
as a localized, Keplerian NIR feature within a gas-depleted, annular dust gap at ≈38 au. The SiS
emission is located along an azimuthal arc and has a similar morphology as a known 12CO kinematic
excess. This is the first tentative detection of SiS emission in a protoplanetary disk and suggests that
the planet is driving sufficiently strong shocks to produce gas-phase SiS. We also report the discovery of
compact 12CO and 13CO J=3–2 emission coincident with the planet location. Taken together, a planetdriven outflow provides the best explanation for the properties of the observed chemical asymmetries.
We also resolve a bright, azimuthally-asymmetric SO ring at ≈24 au. While most of this SO emission
originates from ice sublimation, its asymmetric distribution implies azimuthal temperature variations
driven by a misaligned inner disk or planet-disk interactions. Overall, the HD 169142 disk shows
several distinct chemical signatures related to giant planet formation and presents a powerful template
for future searches of planet-related chemical asymmetries in protoplanetary disks.
Magnetic field and_wind_of_kappa_ceti_towards_the_planetary_habitability_of_t...Sérgio Sacani
We report magnetic field measurements for κ
1 Cet, a proxy of the young Sun when life arose on Earth. We carry out an analysis
of the magnetic properties determined from spectropolarimetric observations and reconstruct its large-scale surface magnetic
field to derive the magnetic environment, stellar winds and particle flux permeating the interplanetary medium around κ
1 Cet.
Our results show a closer magnetosphere and mass-loss rate of M˙ = 9.7 × 10−13 M yr−1
, i.e., a factor 50 times larger than the
current solar wind mass-loss rate, resulting in a larger interaction via space weather disturbances between the stellar wind and
a hypothetical young-Earth analogue, potentially affecting the planet’s habitability. Interaction of the wind from the young Sun
with the planetary ancient magnetic field may have affected the young Earth and its life conditions.
The Variable Detection of Atmospheric Escape around the Young, Hot Neptune AU...Sérgio Sacani
This document summarizes observations from the Hubble Space Telescope of the young hot Neptune exoplanet AU Mic b, which orbits the nearby M dwarf star AU Mic. The observations aimed to detect atmospheric escape of neutral hydrogen through absorption in the stellar Lyman-alpha emission line. Two visits were obtained, one in 2020 and one in 2021, corresponding to transits of the planet. A stellar flare was observed and removed from the first visit data. In the second visit, absorption was detected in the blue wing of the Lyman-alpha line 2.5 hours before the white light transit, indicating the presence of high-velocity neutral hydrogen escaping the planet's atmosphere and traveling toward the observer. Estimates place the column density of this material
Refined parameters of the HD 22946 planetary system and the true orbital peri...Sérgio Sacani
Multi-planet systems are important sources of information regarding the evolution of planets. However, the long-period
planets in these systems often escape detection. These objects in particular may retain more of their primordial characteristics compared
to close-in counterparts because of their increased distance from the host star. HD 22946 is a bright (G = 8.13 mag) late F-type star
around which three transiting planets were identified via Transiting Exoplanet Survey Satellite (TESS) photometry, but the true orbital
period of the outermost planet d was unknown until now.
Aims. We aim to use the Characterising Exoplanet Satellite (CHEOPS) space telescope to uncover the true orbital period of HD 22946d
and to refine the orbital and planetary properties of the system, especially the radii of the planets.
Methods. We used the available TESS photometry of HD 22946 and observed several transits of the planets b, c, and d using CHEOPS.
We identified two transits of planet d in the TESS photometry, calculated the most probable period aliases based on these data, and
then scheduled CHEOPS observations. The photometric data were supplemented with ESPRESSO (Echelle SPectrograph for Rocky
Exoplanets and Stable Spectroscopic Observations) radial velocity data. Finally, a combined model was fitted to the entire dataset in
order to obtain final planetary and system parameters.
Results. Based on the combined TESS and CHEOPS observations, we successfully determined the true orbital period of the planet d
to be 47.42489 ± 0.00011 days, and derived precise radii of the planets in the system, namely 1.362 ± 0.040 R⊕, 2.328 ± 0.039 R⊕, and
2.607 ± 0.060 R⊕ for planets b, c, and d, respectively. Due to the low number of radial velocities, we were only able to determine 3σ
upper limits for these respective planet masses, which are 13.71 M⊕, 9.72 M⊕, and 26.57 M⊕. We estimated that another 48 ESPRESSO
radial velocities are needed to measure the predicted masses of all planets in HD 22946. We also derived stellar parameters for the host
star.
Conclusions. Planet c around HD 22946 appears to be a promising target for future atmospheric characterisation via transmission
spectroscopy. We can also conclude that planet d, as a warm sub-Neptune, is very interesting because there are only a few similar
confirmed exoplanets to date. Such objects are worth investigating in the near future, for example in terms of their composition and
internal structure.
The harps n-rocky_planet_search_hd219134b_transiting_rocky_planetSérgio Sacani
Usando o espectrógrafo HARPS-N acoplado ao Telescopio Nazionale Galileo no Observatório de Roque de Los Muchachos, nas Ilhas Canárias, os astrônomos descobriram três exoplanetas, classificados como Super-Terras e um gigante gasoso orbitando uma estrela próxima, chamada de HD 219134.
A HD 219134, também conhecida como HR 8832 é uma estrela do tipo anã-K de quinta magnitude, localizada a aproximadamente 21 anos-luz de distância da Terra, na constelação de Cassiopeia.
A estrela é levemente mais fria e menos massiva que o nosso sol. Ela é tão brilhante que pode ser observada a olho nu.
O sistema planetário HD 219134, abriga um planeta gigante gasoso externo e três planetas internos classificados como super-Terras, um dos quais transita em frente à estrela.
The kepler 10_planetary_system_revisited_by_harpsSérgio Sacani
This document discusses observations of the Kepler-10 planetary system made with the HARPS-N spectrograph. The observations resulted in improved precision for the masses of Kepler-10b and Kepler-10c. Kepler-10b's mass was determined to be 3.33 ± 0.49 Earth masses, confirming its rocky composition. Kepler-10c's mass of 17.2 ± 1.9 Earth masses makes it the first strong evidence of a class of more massive solid Neptune-sized planets with longer orbital periods. The improved mass measurements will help constrain models of the internal structure and composition of these planets.
Similar to Exoplanet transit spectroscopy_using_wfc3 (20)
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆Sérgio Sacani
Context. The early-type galaxy SDSS J133519.91+072807.4 (hereafter SDSS1335+0728), which had exhibited no prior optical variations during the preceding two decades, began showing significant nuclear variability in the Zwicky Transient Facility (ZTF) alert stream from December 2019 (as ZTF19acnskyy). This variability behaviour, coupled with the host-galaxy properties, suggests that SDSS1335+0728 hosts a ∼ 106M⊙ black hole (BH) that is currently in the process of ‘turning on’. Aims. We present a multi-wavelength photometric analysis and spectroscopic follow-up performed with the aim of better understanding the origin of the nuclear variations detected in SDSS1335+0728. Methods. We used archival photometry (from WISE, 2MASS, SDSS, GALEX, eROSITA) and spectroscopic data (from SDSS and LAMOST) to study the state of SDSS1335+0728 prior to December 2019, and new observations from Swift, SOAR/Goodman, VLT/X-shooter, and Keck/LRIS taken after its turn-on to characterise its current state. We analysed the variability of SDSS1335+0728 in the X-ray/UV/optical/mid-infrared range, modelled its spectral energy distribution prior to and after December 2019, and studied the evolution of its UV/optical spectra. Results. From our multi-wavelength photometric analysis, we find that: (a) since 2021, the UV flux (from Swift/UVOT observations) is four times brighter than the flux reported by GALEX in 2004; (b) since June 2022, the mid-infrared flux has risen more than two times, and the W1−W2 WISE colour has become redder; and (c) since February 2024, the source has begun showing X-ray emission. From our spectroscopic follow-up, we see that (i) the narrow emission line ratios are now consistent with a more energetic ionising continuum; (ii) broad emission lines are not detected; and (iii) the [OIII] line increased its flux ∼ 3.6 years after the first ZTF alert, which implies a relatively compact narrow-line-emitting region. Conclusions. We conclude that the variations observed in SDSS1335+0728 could be either explained by a ∼ 106M⊙ AGN that is just turning on or by an exotic tidal disruption event (TDE). If the former is true, SDSS1335+0728 is one of the strongest cases of an AGNobserved in the process of activating. If the latter were found to be the case, it would correspond to the longest and faintest TDE ever observed (or another class of still unknown nuclear transient). Future observations of SDSS1335+0728 are crucial to further understand its behaviour. Key words. galaxies: active– accretion, accretion discs– galaxies: individual: SDSS J133519.91+072807.4
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...Sérgio Sacani
We present the JWST discovery of SN 2023adsy, a transient object located in a host galaxy JADES-GS
+
53.13485
−
27.82088
with a host spectroscopic redshift of
2.903
±
0.007
. The transient was identified in deep James Webb Space Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Photometric and spectroscopic followup with NIRCam and NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR color, and spectroscopic information all consistent with a Type Ia classification. Despite its classification as a likely SN Ia, SN 2023adsy is both fairly red (
�
(
�
−
�
)
∼
0.9
) despite a host galaxy with low-extinction and has a high Ca II velocity (
19
,
000
±
2
,
000
km/s) compared to the general population of SNe Ia. While these characteristics are consistent with some Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter than the low-
�
Ca-rich population. Although such an object is too red for any low-
�
cosmological sample, we apply a fiducial standardization approach to SN 2023adsy and find that the SN 2023adsy luminosity distance measurement is in excellent agreement (
≲
1
�
) with
Λ
CDM. Therefore unlike low-
�
Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication that SN Ia standardized luminosities change significantly with redshift. A larger sample of distant SNe Ia is required to determine if SN Ia population characteristics at high-
�
truly diverge from their low-
�
counterparts, and to confirm that standardized luminosities nevertheless remain constant with redshift.
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...Sérgio Sacani
Wereport the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The first I-band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in the R-band. There is a big change in the R–I spectral index by 1.0 ±0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ287 as well as the dense monitoring sample of Krakow.
Candidate young stellar objects in the S-cluster: Kinematic analysis of a sub...Sérgio Sacani
Context. The observation of several L-band emission sources in the S cluster has led to a rich discussion of their nature. However, a definitive answer to the classification of the dusty objects requires an explanation for the detection of compact Doppler-shifted Brγ emission. The ionized hydrogen in combination with the observation of mid-infrared L-band continuum emission suggests that most of these sources are embedded in a dusty envelope. These embedded sources are part of the S-cluster, and their relationship to the S-stars is still under debate. To date, the question of the origin of these two populations has been vague, although all explanations favor migration processes for the individual cluster members. Aims. This work revisits the S-cluster and its dusty members orbiting the supermassive black hole SgrA* on bound Keplerian orbits from a kinematic perspective. The aim is to explore the Keplerian parameters for patterns that might imply a nonrandom distribution of the sample. Additionally, various analytical aspects are considered to address the nature of the dusty sources. Methods. Based on the photometric analysis, we estimated the individual H−K and K−L colors for the source sample and compared the results to known cluster members. The classification revealed a noticeable contrast between the S-stars and the dusty sources. To fit the flux-density distribution, we utilized the radiative transfer code HYPERION and implemented a young stellar object Class I model. We obtained the position angle from the Keplerian fit results; additionally, we analyzed the distribution of the inclinations and the longitudes of the ascending node. Results. The colors of the dusty sources suggest a stellar nature consistent with the spectral energy distribution in the near and midinfrared domains. Furthermore, the evaporation timescales of dusty and gaseous clumps in the vicinity of SgrA* are much shorter ( 2yr) than the epochs covered by the observations (≈15yr). In addition to the strong evidence for the stellar classification of the D-sources, we also find a clear disk-like pattern following the arrangements of S-stars proposed in the literature. Furthermore, we find a global intrinsic inclination for all dusty sources of 60 ± 20◦, implying a common formation process. Conclusions. The pattern of the dusty sources manifested in the distribution of the position angles, inclinations, and longitudes of the ascending node strongly suggests two different scenarios: the main-sequence stars and the dusty stellar S-cluster sources share a common formation history or migrated with a similar formation channel in the vicinity of SgrA*. Alternatively, the gravitational influence of SgrA* in combination with a massive perturber, such as a putative intermediate mass black hole in the IRS 13 cluster, forces the dusty objects and S-stars to follow a particular orbital arrangement. Key words. stars: black holes– stars: formation– Galaxy: center– galaxies: star formation
JAMES WEBB STUDY THE MASSIVE BLACK HOLE SEEDSSérgio Sacani
The pathway(s) to seeding the massive black holes (MBHs) that exist at the heart of galaxies in the present and distant Universe remains an unsolved problem. Here we categorise, describe and quantitatively discuss the formation pathways of both light and heavy seeds. We emphasise that the most recent computational models suggest that rather than a bimodal-like mass spectrum between light and heavy seeds with light at one end and heavy at the other that instead a continuum exists. Light seeds being more ubiquitous and the heavier seeds becoming less and less abundant due the rarer environmental conditions required for their formation. We therefore examine the different mechanisms that give rise to different seed mass spectrums. We show how and why the mechanisms that produce the heaviest seeds are also among the rarest events in the Universe and are hence extremely unlikely to be the seeds for the vast majority of the MBH population. We quantify, within the limits of the current large uncertainties in the seeding processes, the expected number densities of the seed mass spectrum. We argue that light seeds must be at least 103 to 105 times more numerous than heavy seeds to explain the MBH population as a whole. Based on our current understanding of the seed population this makes heavy seeds (Mseed > 103 M⊙) a significantly more likely pathway given that heavy seeds have an abundance pattern than is close to and likely in excess of 10−4 compared to light seeds. Finally, we examine the current state-of-the-art in numerical calculations and recent observations and plot a path forward for near-future advances in both domains.
Anti-Universe And Emergent Gravity and the Dark UniverseSérgio Sacani
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional ‘dark’ gravitational force describing the ‘elastic’ response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton’s constant and the Hubble acceleration scale a0 = cH0, and provide evidence for the fact that this additional ‘dark gravity force’ explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
Skybuffer SAM4U tool for SAP license adoptionTatiana Kojar
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SAM4U, an SAP complimentary software asset management tool for customers, delivers a detailed and well-structured overview of license inventory and usage with a user-friendly interface. We offer a hosted, cost-effective, and performance-optimized SAM4U setup in the Skybuffer Cloud environment. You retain ownership of the system and data, while we manage the ABAP 7.58 infrastructure, ensuring fixed Total Cost of Ownership (TCO) and exceptional services through the SAP Fiori interface.
FREE A4 Cyber Security Awareness Posters-Social Engineering part 3Data Hops
Free A4 downloadable and printable Cyber Security, Social Engineering Safety and security Training Posters . Promote security awareness in the home or workplace. Lock them Out From training providers datahops.com
This presentation provides valuable insights into effective cost-saving techniques on AWS. Learn how to optimize your AWS resources by rightsizing, increasing elasticity, picking the right storage class, and choosing the best pricing model. Additionally, discover essential governance mechanisms to ensure continuous cost efficiency. Whether you are new to AWS or an experienced user, this presentation provides clear and practical tips to help you reduce your cloud costs and get the most out of your budget.
leewayhertz.com-AI in predictive maintenance Use cases technologies benefits ...alexjohnson7307
Predictive maintenance is a proactive approach that anticipates equipment failures before they happen. At the forefront of this innovative strategy is Artificial Intelligence (AI), which brings unprecedented precision and efficiency. AI in predictive maintenance is transforming industries by reducing downtime, minimizing costs, and enhancing productivity.
Fueling AI with Great Data with Airbyte WebinarZilliz
This talk will focus on how to collect data from a variety of sources, leveraging this data for RAG and other GenAI use cases, and finally charting your course to productionalization.
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Chris Jones, Director of Product Management at BrainChip , presents the “Temporal Event Neural Networks: A More Efficient Alternative to the Transformer” tutorial at the May 2024 Embedded Vision Summit.
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Integration with BrainChip’s Akida neuromorphic hardware IP further enhances TENNs’ capabilities, enabling the realization of highly capable, portable and passively cooled edge devices. This presentation delves into the technical innovations underlying TENNs, presents real-world benchmarks, and elucidates how this cutting-edge approach is positioned to revolutionize edge AI across diverse applications.
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- Understand the fundamentals of anomaly detection and its importance in identifying unusual behavior or failures in systems.
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- Get to know Prometheus, an open-source monitoring and alerting toolkit, and its application in monitoring edge devices.
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Join HCL Ambassador Marc Thomas in this webinar with a special guest appearance from Franz Walder. It will give you the tools and know-how to stay on top of what is going on with Domino licensing. You will be able lower your cost through an optimized configuration and keep it low going forward.
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Exoplanet transit spectroscopy_using_wfc3
1. Draft Version; not for circulation
A
Preprint typeset using L TEX style emulateapj v. 04/17/13
EXOPLANET TRANSIT SPECTROSCOPY USING WFC3: WASP-12 B, WASP-17 B, AND WASP-19 B
Avi M. Mandell1,7 , Korey Haynes1,2 , Evan Sinukoff3 , Nikku Madhusudhan4 , Adam Burrows5 , Drake Deming6
arXiv:1310.2949v1 [astro-ph.EP] 10 Oct 2013
Draft Version; not for circulation
ABSTRACT
We report analysis of transit spectroscopy of the extrasolar planets WASP-12 b, WASP-17 b, and
WASP-19 b using the Wide Field Camera 3 on the HST. We analyze the data for a single transit
for each planet using a strategy similar in certain aspects to the techniques used by Berta et al.
(2012), but we extend their methodology to allow us to correct for channel- or wavelength-dependent
instrumental effects by utilizing the band-integrated time series and measurements of the drift of the
spectrum on the detector over time. We achieve almost photon-limited results for individual spectral
bins, but the uncertainties in the transit depth for the the band-integrated data are exacerbated
by the uneven sampling of the light curve imposed by the orbital phasing of HST’s observations.
Our final transit spectra for all three objects are consistent with the presence of a broad absorption
feature at 1.4 µm potentially due to water. However, the amplitude of the absorption is less than that
expected based on previous observations with Spitzer, possibly due to hazes absorbing in the NIR
or non-solar compositions. The degeneracy of models with different compositions and temperature
structures combined with the low amplitude of any features in the data preclude our ability to place
unambiguous constraints on the atmospheric composition without additional observations with WFC3
to improve the S/N and/or a comprehensive multi-wavelength analysis.
Subject headings: planetary systems - planets and satellites: atmospheres - planets and satellites:
gaseous planets - infrared: planetary systems - techniques: spectroscopic - methods:
data analysis
1. INTRODUCTION
Over the past decade there has been significant
progress in characterizing exoplanets orbiting a wide variety of nearby stars, including the first detections of
light emitted by an exoplanet (Charbonneau et al. 2005;
Deming et al. 2005), the first spectrum of an exoplanet
(Richardson et al. 2007; Grillmair et al. 2007; Swain et al.
2008), the first phase curve for an exoplanet (Knutson
et al. 2007), the first detection of haze in an exoplanetary
atmosphere (Pont et al. 2008), and tentative constraints
claimed for the water, methane, carbon monoxide and
carbon dioxide abundances in several exoplanetary atmospheres (Grillmair et al. 2008; Swain et al. 2008, 2009b,a;
Madhusudhan & Seager 2009; Madhusudhan et al. 2011).
Almost 100 transiting exoplanets with Vstar < 12 have
been discovered to date, many with multi-band photometry from both space and ground-based observatories. We
are firmly in the era of exoplanet characterization, and
yet the sparse data available for each planet has resulted
in more questions than answers.
The Wide Field Camera 3 (WFC3) on the Hubble Space
Telescope (HST) provides the potential for spectroscopic
1 Solar System Exploration Division, NASA Goddard Space
Flight Center, Greenbelt, MD 20771, USA
2 School of Physics, Astronomy, and Computational Sciences,
George Mason University, Fairfax, VA 22030, USA
3 Institute for Astronomy, University of Hawaii, Honolulu, HI
96822, USA
4 Yale Center for Astronomy and Astrophysics, Yale University, New Haven, CT 06511, USA
5 Department of Astrophysical Sciences, Princeton University,
Princeton, NJ 08544, USA
6 Department of Astronomy, University of Maryland, College
Park, MD 20742, USA
7 Corresponding Email: Avi.Mandell@nasa.gov
characterization of molecular features in exoplanet atmospheres, a capability that has not existed in space
since the demise of NICMOS on HST and the IRS on
Spitzer. WFC3 is an optical/NIR camera capable of slitless grism spectroscopy, with wavelength coverage in the
the IR spanning between 0.8 and 1.7 µm. Studies of exoplanets have focused on using the G141 grism, the longwavelength dispersion element on the infrared channel
that covers the wavelength range 1.1 µm to 1.7 µm at
a maximum resolving power of 130 at 1.4 µm (Dressel
2012). This region spans both the major bands of water
between 1.3 and 1.5 µm as well as another water band
at 1.15 µm, and bands of a few other molecular species.
Observations measuring flux within NIR water bands are
impossible from the ground due to the extinction and
variability caused by water vapor in Earth’s atmosphere;
WFC3 therefore represents the only current platform for
measuring absorption and/or emission from water in exoplanet atmospheres.
In this paper we present WFC3 observations of three
transiting “hot Jupiter” exoplanets — WASP-12 b,
WASP-17 b, and WASP-19 b — during transit of the
host star. Two of these data sets, for WASP-17 b and
WASP-19 b, were observed as part of a large HST program to examine single transits and occultations from
16 hot Jupiters (P.I. D. Deming), while the data for the
transit of WASP-12 b were taken as part of a singleobject campaign (P.I. M. Swain) and first analyzed in
Swain et al. (2013). All three planets orbit extremely
close to their parent star and have large atmospheric
scale heights, making them excellent targets for transmission spectroscopy. WASP-12 b and WASP-17 b (as
well as WASP-19 b to a lesser extent) belong to a class
of “bloated” or “inflated” planets, which have signifi-
2. 2
cantly larger radii than would be predicted from traditional evolutionary models (Burrows et al. 2000; Guillot
& Showman 2002). WASP-17 b is also in a retrograde
orbit compared to the rotation of its host star (Anderson
et al. 2010; Bayliss et al. 2010; Triaud et al. 2010), while
WASP-12 b and WASP-19 b appear to be in prograde
orbits (Albrecht et al. 2012; Hellier et al. 2011). Retrograde orbits have commonly been interpreted as evidence
that the planet was forced into a highly inclined and eccentric orbit through planet-planet scattering (Rasio &
Ford 1996; Weidenschilling & Marzari 1996) or the Kozai
mechanism (Fabrycky & Tremaine 2007), and was subsequently re-circularized through dissipation of orbital energy by tides (Jackson et al. 2008). The extremely short
orbit of WASP-19 b also argues for tidal decay after scattering (Hellier et al. 2011). In the tidal decay scenario the
large radii of the planets could be due to internal dissipation of tidal energy during orbital circularization (Bodenheimer et al. 2001). However, based on recent models
by Ibgui & Burrows (2009), Anderson et al. (2011) conclude that any transient tidal heating produced during
circularization of the orbit of WASP-17 b would have dissipated by the time the planet reached its current orbit,
making the planet’s large radius unsustainable. Other
theories for the misalignment of the stellar rotation and
the planet’s orbit do not require a previous eccentric orbit and tidal re-circularization (Rogers et al. 2012), and
a number of other theories for the heating mechanisms
required to produce large planetary radii have been proposed, including “kinetic heating” due to the dissipation
of wind energy deep in the atmosphere (Guillot & Showman 2002) and Ohmic dissipation (Batygin & Stevenson
2010); therefore the dynamical origin of these extremely
hot and inflated giant planets is still highly uncertain.
In principle, understanding the atmospheric composition of hot Jupiters can help constrain their formation
and dynamical histories. Unfortunately, observational
studies have produced conflicting results regarding the
atmospheric compositions of several hot Jupiters, including WASP-12 b and WASP-19 b. Madhusudhan et al.
(2011) first raised the possibility of a non-solar abundance in the atmosphere of WASP-12 b using occultation measurements in four Spitzer photometric bands
(Campo et al. 2011) and three ground-based NIR photometric bands (Croll et al. 2011) to constrain the carbonto-oxygen ratio to super-solar values, possibly greater
than unity. Similar Spitzer and ground-based measurements for WASP-19 b were consistent with both solar
and super-solar C/O models (Anderson et al. 2013), raising the possibility of a population of carbon-rich hot
Jupiters. However, Crossfield et al. (2012) recently reanalyzed the Spitzer data for WASP-12 b in light of
the discovery of a faint candidate companion imaged
by Bergfors et al. (2013), concluding that the dilutioncorrected Spitzer and ground-based photometry can be
fit by solar-metallicity models with almost isothermal
temperature structures.
While transmission spectroscopy only weakly constrains the overall temperature structure of a transiting
exoplanet, it can place strong constraints on the presence
of molecular features in absorption through the limb of
the planet, thereby constraining the atmospheric composition. Models by Madhusudhan (2012) suggest that
spectral features of H2 O and hydrocarbons (e.g. CH4 ,
TABLE 1
Observation Parameters
WASP-12
Date of Observation
Integration Time
Subarray Mode
CALWF3 version
NSamp
Timing Sequence
Peak Pixel Value1
WASP-17
WASP-19
2011-04-12
7.624
256
2.7
3
SPARS10
38,000
2011-07-08
12.795
512
2.3
16
RAPID
64,000
2011-07-01
21.657
128
2.3
5
SPARS10
73,000
1 The number of electrons recorded at the peak of the spectral
distribution in a single exposure.
HCN, and C2 H2 ) will change drastically with different
C/O values, and the WFC3 bandpass covers several of
these features. In this paper we present our data reduction and analysis of the three transits, including our
analysis of contamination from nearby sources and our
strategy to compensate for the significant instrumental
systematics in much of the WFC3 data, and conclude
with preliminary constraints on the atmospheric composition and structure of the three planets.
2. OBSERVATIONS
The observations of WASP-17 and WASP-19 analyzed
here were conducted between June and July of 2011,
while the observations of WASP-12 were obtained in
April of 2011. Observation dates and exposure information are listed in Table 1. The observations were
taken with the G141 grism on WFC3’s infrared channel,
providing slitless spectra covering the wavelength range
1.1 µm to 1.7 µm at a maximum resolving power of 130
at 1.4 µm (Dressel 2012). Dithering was avoided to minimize variations in pixel-to-pixel sensitivity. The “spatial
scanning” mode suggested as a strategy to increase efficiency and decrease persistence for bright objects (McCullough & MacKenty 2012) was not used since it had
not been developed at the time of observation. Each target was allocated 4–5 HST orbits, each lasting 90 minutes
followed by 45 minute gaps due to Earth occultations of
the telescope. This was sufficient to cover a single transit
while including some out-of-transit data as well.
The IR channel of the WFC3 instrument uses a 1024
x 1024 pixel detector array, but smaller sub-arrays can
be downloaded to decrease the readout time and increase
the exposure cadence. Additionally, there are two possible sampling sequences: RAPID sampling, which reads
as quickly as possible (limited only by the readout time
per sub-array) in order to maximize sampling for short
exposures of bright targets, and SPARS sampling, which
takes two quick reads and then spaces reads linearly,
to allow “sampling up the ramp”, or SUTR. RAPID
sampling naturally has shorter readout times for each
sub-array size but imposes a maximum integration time,
while the SPARS10 sampling sequence has a minimum
exposure time of ∼7 sec but no maximum.
Observations of WASP-17 were taken using the 512 x
512 sub-array with 16 non-destructive reads per exposure
and sampled using the RAPID sampling sequence. This
resulted in a total integration time of 12.795 seconds per
exposure and 27 exposures per orbit, with a total of 131
exposures taken over five HST orbits. Observations of
WASP-19 were taken using the 128 x 128 sub-array mode
3. 3
3. DATA REDUCTION
3.1. Image Files: .flt vs .ima
The WFC3 calwf3 calibration pipeline processes the
raw detector output into two calibrated files per exposure: a file comprising the individual, non-destructive
reads (called the .ima file) and a single final image produced by determining the flux rate by fitting a line to the
individual read-out values for each pixel (called the .flt
file). The calibration steps implemented for the .ima
files include reference pixel subtraction, zero-read and
dark current subtraction, and a non-linearity correction;
additional corrections applied using SUTR fitting for the
.flt files include cosmic-ray and bad-pixel flagging and
gain calibration. While it would seem that the .flt files
would be the best choice for analysis, an analysis of the
noise characteristics for each data type revealed that time
series extracted from the .flt files have an rms that is
on average 1.3× greater than time series created from
the .ima files. It is unclear where this difference originates, though it is probably due to inaccurate cosmic ray
flagging for very bright sources (STScI WFC3 Support,
private communication); we therefore decided to determine our own flux values for each pixel directly from the
.ima files and essentially re-create our own .flt files as
a starting point for our analysis (this method was also
advocated by Swain et al. (2013) for similar reasons).
Though the .ima files include a linearity correction, the
exposures for some our objects approached or exceeded
the established linearity limit for WFC3 and we therefore examined our data for signs of any remaining nonlinearity. The WFC3 detector generally remains linear
up to 78K e− (WFC3 Handbook); however, Swain et al.
(2013) suggest that known WFC3 issues with systematic
increases in counts between buffer downloads (see §4.1)
may be present when count levels exceed 40K DN, or the
equivalent of 100K e− . Our peak counts reach a maximum of 73K e− for WASP-19, with lower values for our
other targets (see Table 1); we therefore chose WASP19 to examine linearity. WASP-19 only has a total of 4
SUTR measurements; in Figure 1 we show that the normalized rms of our band-integrated light curve follows
the expected decrease for a photon-limited case. We also
examined the linearity of each channel separately, in order to search for correlations with the final transit depth.
Deviations from linearity were ∼0.8% on average, but
the channel-to-channel differences were only ∼0.1% and
would affect the transit depths for individual channels by
only ∼20 ppm, far below our uncertainty limits. After
binning up channels, this effect would be even less; we
therefore did not use any additional linearity correction.
3.2. Spectral Extraction
WASP-19 Linearity Test
Normalized RMS
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
2.030
Transit Depth (%)
with 5 non-destructive reads per exposure, sampled with
the SPARS10 sequence. This resulted in an integration
time of 21.657 seconds and 70 exposures per orbit, with a
total of 274 exposures taken over four orbits. The WASP12 data utilized the 256 x 256 sub-array mode with 3 nondestructive reads per exposure, leading to an integration
time of 7.624 seconds and 99 exposures per orbit, with
484 exposures taken over five HST orbits. We discuss
the implications of each sub-array size with respect to
systematic trends in §4.1.
RMS
Expected Photon Noise
2.025
2.020
2.015
2.010
2.005
2.000
6
7
8 9 10
Log Exposure Length (seconds)
20
Fig. 1.— Top: The normalized rms compared to expected photon
noise for a band-integrated light curve for WASP-19 created using
different individual reads. Bottom: Fitted transit depth for each
read. The rms follows the photon-limited trend except for the first
point, which most likely reflects read noise; the best-fit values are
the same within uncertainties.
The unique requirements of time-series photometry of
bright sources necessitated the development of a customdesigned data reduction process for WFC3 exoplanet
data. A data reduction package called aXe (K¨mmel
u
et al. 2009) exists for analyzing WFC3 data, but this software was designed with dithered observations in mind,
and we used the package only for generating a wavelength solution and nominal extraction box sizes since
the package incorporates the most recent configuration
files for the instrument. An object list was first generated by SExtractor (Bertin & Arnouts 1996), which
uses the direct image to find the position of each source.
aXe then calculates the trace and wavelength solution for
each source, and produces FITS files with an extracted
box from each grism image (with the extension .stp) and
a 1D spectrum (with the extension .spc) from which we
extract the wavelength solution. For simplicity, we assumed that each pixel in a column has the same wavelength solution; measurements of the center of a Gaussian fit to the dispersion in the y direction showed that
it changes by less than 0.02 pixel along the length of
the spectra for all of our objects, so this assumption is
valid. We also checked our wavelength solutions against
the standard WFC3 sensitivity function to confirm accuracy for all sources.
We retrieved the coordinates for the extraction box
from the headers of the .stp files, but we decided to expand the number of rows included in the extraction box
from 15 pixels to 20 pixels to ensure that we included as
much of the wings of the spatial PSF as possible while
avoiding any possible contamination from background
sources. We also trimmed the extraction boxes to exclude regions of the spectrum with low S/N, keeping the
central 112 pixels of each spectrum.
3.3. Flat Field, Background Subtraction, Bad Pixel and
Cosmic Ray Correction
The calwf3 pipeline does not correct for pixel-to-pixel
variations in grism images, but a flat-field cube is provided on the WFC3 website (Kuntschner et al. 2008).
4. 4
Each extension of the cube contains a coefficient, developed by ground tests, that can be fed into a polynomial
function as follows, where x = (λ − λmin )/(λmax − λmin )
and λ is the wavelength of pixel (i,j):
f (i, j, x) = a0 + a1 ∗ x + a2 ∗ x2 + ...ai ∗ xn
(1)
This polynomial gives the value of the flat field at
each pixel in the extraction region, and we divided this
flat field from our data. We also subtracted an average background flux from each spectral channel by using
nearby uncontaminated regions of each image. These
background regions cover the same wavelength space (extent in the x direction) as our science box, and are placed
as far from the primary source as possible, leaving only
a few pixels to guard against edge effects. We then averaged these background rows in the y direction, and
subtracted this background spectra from each row of our
science box. The average value of the background region was ∼15 - 35 e− , but for each source background
counts drop quickly at the beginning of each orbit and
then continue to decrease slowly over the orbital duration
(see Figure 2). The pattern is very similar in each channel, and is most likely due to thermal variations during
the orbit.
Counts
35
WASP-12
4. ANALYSIS AND RESULTS
30
4.1. Instrumental Systematics
25
Two out of our three data sets show strong systematic trends with time, which can be attributed to various
instrumental effects, and have been seen in previous observations (Berta et al. 2012; Swain et al. 2013). The
most obvious trend is the pattern of increasing counts
after each data buffer download to the solid-state drive,
possibly due to the use of charge-flush mode during
the download (Swain et al. 2013). Depending on how
quickly the count level stabilizes, this pattern can resemble a “ramp” (continually increasing until the next buffer
download) or a “hook” (increasing for several exposures
and then stabilizing). The effect may be associated with
the well-known persistence effects inherent in HgCdTe
detectors in general (Smith et al. 2008) and confirmed in
WFC3 in particular (McCullough & Deustua 2008), but
the relationship to the data buffer downloads suggests
a connection to the data storage devices. Swain et al.
(2013) performed an exhaustive analysis of the bufferramp effects in a number of different sources, and suggest that a smaller sub-array size, a fewer number of
non-destructive reads, and a lower illumination level will
decrease or eliminate the effect; for reference, we list the
relevant attributes for each target in Table 1. The bandintegrated light curves (Figure 3) for the three objects
we analyze here follow this general relationship - WASP12 (intermediate array size, 3 reads, low peak pixel flux)
has no buffer-ramp effect, while WASP-17 (large array
size, 16 reads, high peak pixel flux) has a very steep
ramp-up with no apparent stabilization before the next
buffer dump. WASP-19 (small array size, 5 reads, high
peak pixel flux) displays a shape intermediate between
the two (a “hook”-like shape). We do not attempt a
more detailed analysis of the cause of the buffer-ramp
effects; we find that the divide-oot method developed by
20
−0.20
−0.15
−0.10
−0.05
0.00
0.05
0.10
0.15
Counts
30 WASP-17
25
20
−0.25
−0.20
45
WASP-19
Counts
these pixels through spatial interpolation in their individual frames; however, the linear interpolation that we
used to correct bad pixels would clearly not be effective
within the region covered by the stellar PSF due to the
rapid change in flux across pixels in the spatial direction.
Bad pixels within the PSF would also clearly have severe
effects on the time series even if they were corrected, and
we therefore left these pixels uncorrected.
We then summed over the spatial dimension of the corrected cube yielding a 2D (wavelength, time) array and
normalized this array in both the spectral and temporal
dimensions, allowing us to remove the band-integrated
transit signal and the stellar and instrumental spectral
characteristics. This allowed us to identify both bad
spectral channels in individual images as well as individual images and/or channels that showed increased
noise or unusual characteristics. Through this analysis
we found 20 individual bad data points for WASP-12, 6
for WASP-17, and 16 for WASP-19, which we corrected
by linear interpolation in the spectral dimension. Additionally, we identified several spectral channels in each
data set whose time series showed a significantly higher
rms scatter compared with the rest of the channels; we
removed 2 channels for WASP-12, 4 channels for WASP17, and 1 channel for WASP-19 from further analysis as
well.
−0.15
−0.10
−0.05
0.00
0.05
0.05
0.10
40
35
30
−0.20
−0.15
−0.10
−0.05
0.00
Time From Mid-transit (days)
Fig. 2.— Background levels in counts for each target, given as a
function of time from mid-transit. The drop in flux on a per-orbit
basis is similar for each target, indicating that instrumental effects
such as thermal variations during orbit are the likely cause.
To identify pixels that are either permanently bad or
contaminated by cosmic rays, we employed several different bad pixel identification strategies. First, to find
individual pixels in individual images that were contaminated by cosmic rays or sensitivity variations, we created
a 3D image cube and examined each pixel in the 2D images over time; any single-image pixels that were > 6σ
higher than the median of their counterparts in time were
flagged. We found 62 bad pixels for WASP-12, 30 for
WASP-17, and 120 for WASP-19. We corrected most of
5. 5
Berta et al. (2012) is sufficient to remove the effect almost
completely in the band-integrated light curve provided
sufficient out-of-transit data is available. We also see a
visit-long decrease in flux; this effect has been noted in
previous WFC3 analyses and may be due to a slow dissipation of persistence charge, and we correct for it using a
linear trend component in our transit model fit. As noted
in previous work, the first orbit for each target showed
substantially higher scatter than all other orbits, and we
do not use this orbit in our band-integrated divide-oot
analysis; however, for our wavelength-dependent analysis we use a relative-depth analysis (see §4.3 and §4.4 for
a detailed description), and with this fitting strategy we
are able to incorporate the first noisier orbit.
1.02
1.01
1.00
Normalized Flux
0.0
0.05
0.10
0.15
1.010
1.005
1.000
0.995
0.990 WASP-17
Raw B.-Int. Lightcurve
0.985 After Divide-OOT
Best Fit
0.980
-0.25
-0.20
-0.15
-0.10
-0.05
0.0
-0.05
Residuals
1.01
1.00
0.99
0.98
WASP−17 Systematic Trends
WASP-19
Raw B.-Int. Lightcurve
After Divide-OOT
Best Fit
0.0
-0.15
-0.10
-0.05
Time From Mid-transit (days)
0.05
Fig. 3.— The combined-light time series for each source, before and after removing systematic trends. The presence of an
intra-orbit pattern is easily identified for WASP-17 and WASP-19,
repeating after every buffer read-out, but less obvious for WASP12. After excluding the first orbit which is inconsistent with the
others due to telescope settling, we removed the trends using the
divide-oot method devised by Berta et al. (2012).
For each image, we also calculated the shift in the vertical (i.e. spatial) and horizontal (i.e. spectral) directions
referenced to the first exposure in the time series. This
allowed us to correct for any modulation in channel flux
due to undersampling of the spatial PSF and/or spectral
features. Since the FWHM of the PSF is ∼3 pixels, any
vertical shifts can have a significant effect on the illumination of individual rows, and a similar effect can occur
due to features in the stellar spectrum or the WFC3 sen-
0.002
–0.002
–0.006
Y−Shift (pix)
0.98
1.015
WASP-12
Raw B.-Int. Lightcurve
After Divide-OOT
Best Fit
-0.15
-0.10
-0.05
0.01
–0.01
–0.03;
X−Shift (Å)
0.99
sitivity function that are several pixels wide. However,
the shifts we measure are only a fraction of a pixel (see
Figure 4) and the motion of a pixel across the spatial PSF
or a spectral feature will be extremely small, creating a
change in flux that is essentially linear. We can therefore decorrelate this effect against a scaled measurement
of the image motion in each direction.
We measured the vertical shift by first summing our
extraction box in the wavelength direction to get a 1D
array of the flux absorbed by each row of the detector for
each exposure and then fitting a Gaussian to those arrays
to determine the change in the location of the peak of the
flux distribution from the first exposure. A precise measurement of the horizontal shift (i.e. the spectral shift)
across all exposures was more difficult to calculate, since
the sensitivity function of the grism does not allow for an
analytical fit. We first attempted to cross-correlate the
spectra against each other, but the scatter in the resulting measurements was too high to be useful. We then
decided to utilize the edges of the spectrum where the
sensitivity function of the detector rises and falls rapidly,
and a small change in pixel position will have a strong
effect on the illumination of each pixel. We fit a line to
the slope for the same pixels at the edge of the spectrum
for each exposure, and used the intercept of this fit to
determine the shift of each spectrum in relation to the
first exposure; the values from the fit to both the shortwavelength and long-wavelength edge of each spectrum
were averaged to decrease the effective uncertainty of the
measurement. In Figure 4 the vertical and horizontal
shifts, as well as the final band-integrated residuals after
subtracting a light curve model, are plotted for WASP-17
as an example. All of the variables change relatively coherently within an orbit, and then reset at the beginning
of the next orbit.
2
0
–2
–0.25
–0.20
–0.15
–0.10
–0.05
Time From Mid-Transit (days)
0.0
0.05
Fig. 4.— Top: The residuals of the combined-light fit for WASP17, after subtracting our best-fit model. Middle: The shift in the
position of the spatial profile of WASP-17 over time, in pixels.
The vertical shift was calculated by fitting a Gaussian to sum of
the spectral box in the spectral direction. Bottom: the shift in the
position of the spectral profile over time, in pixels. The horizontal
shift was calculated by measuring the change in flux over the edges
of the spectrum and deriving the required shift of the spectral
sensitivity function (see §4.1).
6. 6
PSF Fit for WASP-12 Channel 63 (1.4192 μm)
3.0×104
Data
Primary PSF
Secondary PSF
Combined Fit
Counts
2.5×104
2.0×104
1.5×104
1.0×104
5.0×103
0
150
∆Counts
4.2. Background Source Correction
We also examined each object for contamination from
background sources. Due to the slitless design of WFC3,
spectra from background sources can be shifted both spatially and spectrally compared with the science target.
In particular, a nearby background source or companion
was discovered for WASP-12 (Bergfors et al. 2013) and
more recently confirmed to be a double star (Bechter
et al. 2013); the close companions have been shown to
significantly affect the mid-IR photometry of this source
with Spitzer (Crossfield et al. 2012). After averaging all
of the images for each source, we examined each combined image by eye for evidence of background contamination, and then used a vertical profile cut to further
constrain the amplitude and location of any identified
sources. For WASP-19 there were no additional sources,
and for WASP-17 the single background source identified nearby was very dim and significantly shifted in the
spatial direction from the science target and therefore
exterior to our extraction box.
For WASP-12 we identified a relatively bright contamination source very close to the science target; the peak
of the spectral profile of the secondary source is located
only ∼4 pixels away from the peak of the primary stellar
PSF in the spatial direction (see Figure 5). This object is
most likely the source identified by Bergfors et al. (2013)
(referred to as Bergfors-6 by Crossfield et al. (2012) and
WASP-12 BC by Bechter et al. (2013)); after correcting for a shift of the the secondary source in the spectral direction, the separation between the two sources
matches up well with the previous measurements. As
stated above, Bechter et al. (2013) resolved the source
into two stars, but in the direct image from HST they
are unresolved - the difference in the FWHM of the primary PSF compared to the secondary PSF is only 0.25
pixels. We therefore refer to the combined contamination
from the two stars in our data as WASP-12 BC. Swain
et al. (2013) also identified this contamination, and fit
the profile of the PSF in the spatial direction by using
the PSF shape from separate observations of a reference
star; this method has the benefit of providing an empirical PSF shape that can be used for both the brighter
primary star as well as the secondary star. This strategy is slightly complicated in this instance because of
the multiplicity of the secondary source, but as stated
above, the change in the width of the PSF is extremely
small. The more difficult problem is that the angle of
the spectrum on the detector is slightly offset from the
horizontal pixel pitch; therefore the PSF changes shape
with wavelength, and the primary and secondary point
spread functions are sampled differently.
Fortunately our WASP-19 spectrum was also slightly
angled on the detector, and since the flux levels remaining in the linear regime we were able to scale individual
channels from our WASP-19 data as PSF “templates”
for the WASP-12 channels (as suggested by Swain et al.
(2013)). The PSF of WASP-12 BC could also be fit in
the same way, albeit with a different initial off-set for the
starting template channel. We empirically determined
the best-fit template channel off-set for both PSFs, and
then performed a least-squares fit for the PSF amplitude of both stars at once. In Figure 5 we show an
example of a fit to one of our WASP-12 channels; the
Residuals
100
50
0
-50
-100
-150
0
5
10
Row Number
15
20
Fig. 5.— Top: Data and the best-fit PSF model for a single
channel for WASP-12, using the template-PSF method. The data
are shown in black, the fit to the main peak is shown in green, and
the fit to the contamination peak is shown in blue; the combined
fit is shown in red. Bottom: Remaining residuals after removing
the model; the remaining flux under the region of contamination
was used as the uncertainty in the contamination flux.
remaining residuals in the region with the contaminating
source will be impacted slightly by the distorted PSF of
the double stars, so we summed them up to give uncertainties on the fit in the positive and negative directions.
In addition to this PSF template strategy, we tested a
straightforward sequential Gaussian fitting method, first
fitting and subtracting the largest-amplitude signal (from
the science target) and then fitting the additional contamination source. However, due to the under-sampling
of the spatial PSFs and their overlap between the two
sources, there was substantial uncertainty in the fundamental baseline of the individual PSF functions for each
source, and considerable residual flux was left over after
removing the contribution from both PSFs. In Figure 6
we plot our spectrum for WASP-12 BC derived from both
methods. The results agree extremely well at short and
long wavelengths except for an overall offset and some
slight discrepancy between 1.35 and 1.45 µm; however,
the uncertainties are at least a factor of 3 smaller using
the template-PSF method, even with the contributing
error from the multiplicity of WASP-12 BC. We therefore adopted the results from the template-PSF fitting
method, and corrected the data by subtracting the derived spectrum of the contaminating source from the 1D
spectrum at each time step.
For comparison, we calculated the expected ratio of
the contaminating source to the primary star using stellar atmosphere models from Castelli & Kurucz (2004),
assuming that the contaminating source is the combined light from WASP-12 B and WASP-12 C. Crossfield et al. (2012) determined a spectral type of M0V
and an effective temperature between 3600 K and 3900
K for what they believed was a single star, depending on
whether purely spectroscopic or a combination of spectroscopic and photometric data were used; for WASP-12,
Hebb et al. (2009) determined an effective temperature
of 6300200 K. Since Bechter et al. (2013) find that both
100
7. 7
Flux Ratio
(WASP-12 BC / WASP-12 A)
0.12
0.10
Gauss Fitting
PSF Fitting
0.08
0.06
0.02
1.1
0.12
0.08
0.04
0.00
Swain et al. 2013
Teff_sec= 3660 K, Teff_pri= 6300K
Teff_sec= 3900 K, Teff_pri= 6500K
PSF Template fitting
0.02
0.04
1.2
1.3
1.4
1.5
Wavelength (μm)
1.6
1.7
Fig. 6.— Flux ratio for WASP-12 BC compared to WASP-12
A for our two fitting methods. Gaussian fitting (black) subtracts
one Gaussian centered on WASP-12’s position, then fits another
Gaussian to the residuals, centered on the contaminating source.
Template PSF fitting (red) jointly scales two PSFs, using predetermined columns from WASP-19 as a template. The uncertainties using the template PSF method are much smaller, even
with the distortions of the secondary PSF due to the multiplicity
of WASP-12 BC.
companions have a similar spectral type and brightness,
we can effectively treat them as one source. We assumed
the same metallicity for all the stars, and used the direct
image to derive a shift of 331 ˚ in the spectral direction
A
for the contaminating source. We then scaled the ratio of two stellar models to match our results at 1.6 µm.
In Figure 7 we plot our results from our PSF template
method, with two analytic models spanning the range
of effective temperatures for WASP-12 A and WASP-12
BC. A lower-temperature model for the combined flux
from WASP-12 BC shows a significantly deeper water
absorption feature from 1.4 to 1.6 µm compared with
higher-temperature models, while a higher temperature
for WASP-12 A makes a very small change in the overall
slope. Our empirical fit to the data agrees very well with
a model using a temperature of ∼3900 K for WASP-12
BC, which matches well with the M0 spectral type derived by Bergfors et al. (2013) and Crossfield et al. (2012)
but is inconsistent with the spectral type of M3V determined by Bechter et al. (2013) for both WASP-12 B and
C.
A similar calculation of the contaminating flux was
used by Stevenson et al. (2013); however, they assumed
the lower effective temperature for WASP-12 BC from
the spectroscopic analysis by Crossfield et al. (2012) a
priori, without attempting to determine the contaminating flux empirically. Alternately, Swain et al. (2013) performed a similar fit to ours, but their results appear to
lack the sharp downturn shortwards of 1.15 µm and the
upturn longwards of 1.55 µm that are evident in our results; the slope of their results is also slightly shallower
(a linear approximation to their results is plotted in Figure 7; they did not publish their fitted values, but they
are close to a single linear trend with a slight decrease
between 1.34 and 1.48 µm). Given the close similarity
between the high-temperature analytical model and our
empirical fit to the data, we remain confident that our
results are robust. However, it is clear that the choice
of the spectral dependence for the dilution by WASP-12
∆ Flux Ratio
Flux Ratio (WASP-12 BC / WASP−12 A)
WASP-12 Contamination Fitting Methods
0.01
0.00
-0.01
-0.02
1.2
1.3
1.4
1.5
Wavelength (μm)
1.6
Fig. 7.— Top: Flux ratio for the contaminating source (WASP12 BC) from the template PSF fitting method (black), compared
with analytical models for the flux ratio bracketing the range of
values for the temperatures of WASP-12 and the contaminating
source (red and green); an approximation to the same values from
Swain et al. (2013) are also plotted (blue). Bottom: the same
analyses as above, but both the analytical models and the Swain
et al. (2013) results have the values from our fitting subtracted,
in order to better show the discrepancies. The results from our
PSF fitting match very closely with the high-temperature limit
for the temperatures of both the primary source (WASP-12 A)
and the contaminating source (WASP-12 BC); the low-temperature
model shows a much larger signature of absorption from water
vapor between 1.35 and 1.6 µm. The Swain et al. (2013) results are
similar at most wavelengths, but there is a very large discrepancy
at the shortest wavelengths.
BC has a significant impact on the final results for the
spectrum of WASP-12 b; uncertainties of 1% for the dilution factor for WASP-12 BC will result in a difference
of 150 ppm in the final transit depth, which is similar
in magnitude to the uncertainties for the transit depths
of our individual bins. We discuss this impact further in
§5.
4.3. Band-Integrated Transit Curve Fitting
Our analysis strategy relies on the assumption that
almost all of the time-dependent trends present in the
band-integrated time series are consistent across wavelength (even if the amplitudes of these trends change),
since the systematics are related to either the general exposure parameters (array size, number of read-outs, etc),
and/or correlated with the illumination of each pixel.
We therefore decided to determine the band-integrated
transit curve parameters first, and then use the residuals
from this band-integrated fit as a component in our transit model when fitting individual spectral channels (with
the amplitude of this component allowed to vary). This
method allows us to incorporate any common-mode systematic trends into our fit, providing a more robust measurement of the relative change in transit depth across
spectral channels, which is the most important factor
when measuring the depth of spectral absorption fea-
8. 8
tures. We are also able to include the first orbit for each
target into the wavelength-dependent analysis since the
higher scatter in this orbit (which has caused most observers to discard it) is common across wavelength and
can be removed accurately. We describe the fitting strategy in more detail in §4.4.
To achieve the best possible fit to the band-integrated
light curve prior to fitting individual spectral bins, we
utilized the divide-oot method developed by Berta et al.
(2012), which uses the systematics in the out-of-transit
data to correct the in-transit data by simply dividing all
orbits by an average of the out-of-transit orbits. This
method works very well to remove the repeated intraorbit slope and buffer-ramp effects, which represent the
largest instrumental effect in our data. We then fit the
corrected light curve with a Markov Chain Monte Carlo
(MCMC) routine with a Metropolis-Hastings algorithm
within the Gibbs sampler (Ford 2005), using the light
curve model from Mandel & Agol (2002), with an additional linear slope term to account for the gradual decrease in flux seen in all WFC3 exoplanet transit data to
date.
All of the orbital parameters in our transit light curve
model were locked to the literature values (see Table 2),
since we are only analyzing single transits and lack fulltransit coverage. The only exceptions are the mid-transit
time and the two parameters for a quadratic limb darkening law, which we allow to vary under Gaussian priors since we are only analyzing a single transit with incomplete coverage of ingress and egress. For mid-transit
times, we calculate the predicted mid-transit time from
recent transit observations of our targets in the literature,
and propagate the uncertainty on period in time to use as
the width of our prior. For limb darkening, we use values
calculated by Claret & Bloemen (2011) from analysis of
ATLAS models. After selecting for the appropriate stellar parameters, Claret & Bloemen (2011) provide values
at the centers of the J and H bands, with a choice between a least-square and flux conservation method. We
interpolated between the J and H band points to find the
central wavelength of our spectra, and took the average
between the two methods as our starting limb-darkening
parameter value. We used the standard deviation between the two methods, multiplied by two, as the width
of our priors.
For each light curve we ran three MCMC chains with
100,000 links for analysis, with an additional initial burn
period of 25,000 links. Our band-integrated time series
for each of our targets are shown in Figure 3, with the
best-fit transit curve overlaid; we tabulate our best-fit orbital parameters in Table 3. Our best-fit limb darkening
parameters compare well with the expected values from
Claret & Bloemen (2011), and best-fit mid-transit times
are within the uncertainties based on prior measurements
(see Figure 8).
4.3.1. Fitting for a Possible Thermal Contribution and
Starspots
After fitting the integrated-light time series using the
standard transit model, we determined that there appeared to be systematic deviations in the residuals of
the out-of-transit orbits for both WASP-12 and WASP19 as well as the in-transit orbit for WASP-19. The
out-of-transit orbits appear to have trends in flux that
LD
Coeff.
0.35
WASP-12
0.30
0.25
0.20
0.15
0.10
LD 1
0.30
0.25
0.20
0.15
0.10
0.05
WASP-17
0.30
0.25
0.20
0.15
0.10
0.05
WASP-19
MJD
55663.X
3999
LD 2
Tmid
3997
55750.X
2960
LD 2
Tmid
LD 1
2950
2940
55743.X
5323
LD 2
Tmid
LD 1
3998
Our values
C.&B. 2011
Our values
Lit. values
5322
5321
Fig. 8.— Limb darkening parameters for a quadratic limb darkening law shown as calculated using models from Claret & Bloemen
(2011), and as found by our MCMC routine, using the Claret &
Bloemen (2011) models and uncertainties as priors. Our final values match the expected values within uncertainties for all targets.
are not perfectly fit by a single linear slope, with the
first orbit having a steeper slope while the last orbit has
a shallower slope (see Figure 9). It is difficult to determine the source of these trends due to the limited
sampling in orbital phase and the necessity of using the
divide-oot correction method, which combines the data
from all out-of-transit orbits (and therefore mixes underlying trends and/or red noise together). The current
data can be fit using a 2nd-order polynomial, or fit using a more physically motivated model including a sinusoidal component with a period equal to the planetary
orbital period, representing the thermal phase variation
due to the day-night temperature difference (Knutson
et al. 2007). Either model results in a better fit to the
data than the linear slope for WASP-12 and WASP-19,
and we decided to use the Bayesian Information Criterion (BIC; Schwarz (1978); Liddle (2004)) to determine
whether the improvements from either of the more complex baseline models was sufficiently significant. The BIC
includes a strong penalty for including additional parameters, and therefore provides a robust technique to distinguish between models; ∆BIC ≥ 2 is considered to be
positive evidence against the null hypothesis. The BIC
was not increased using the non-linear baseline models
for either target (∆BIC ∼ −0.5). However, the best-fit
peak-to-trough amplitude of 0.0018±0.0006 for a possible
sinusoidal component in the WASP-12 data is within the
range predicted for the thermal phase variations of very
hot planets (Cowan & Agol 2011), though it is smaller
than the value measured using Spitzer (Cowan et al.
2012). The best-fit amplitude for WASP-19 is similar
to WASP-12 (0.0016±0.0007). We conclude that due to
the low significance of the fit, the limited time sampling
and ambiguities introduced by the divide-oot method,
the nature of the curvature is highly uncertain and must
therefore be investigated with more complete observa-
9. 9
TABLE 2
Stellar and Orbital Parameters Used For Model Fitting and Comparison
Parameters
WASP-12 ba
WASP-17 bb
WASP-19 bc
Period (days)
i (◦ )
Rp /R∗
Tc
µ1 d
µ2
a/R∗
e
ω (◦ )
Semi-major axis (AU)
M∗ (M )
Mp ×sin i (MJ )
Spectral type
H-band Magnitude
[Fe/H]
1.09
82.5 ± 0.8
0.117 ± 0.00068
55663.199
0.127 ± 0.0487
0.271 ± 0.0620
3.03 ± 0.0220
0.0447 ± 0.00430
94.4 ± 0.0300
0.02309 ± 0.00096
1.38 ± 0.18
1.378 ± 0.181
G0
10.228
0.3 ± 0.1
3.73
86.7 ± 0.500
0.123 ± 0.037
55750.285
0.0901 ± 0.0487
0.273 ± 0.0620
6.96 ± 0.0220
0.00
0.00
0.05105 ± 0.00128
1.286 ± 0.079
0.477 ± 0.033
F4
10.319
-0.25 ± 0.09
0.789
79.5 ± 0.500
0.139 ± 0.0457
55743.532
0.153 ± 0.0487
0.293 ± 0.0620
3.57 ± 0.0460
0.00770 ± 0.00680
43.0 ± 67.0
0.01616 ± 0.00024
0.904 ± 0.040
1.114 ± 0.04
G8V
10.602
0.02 ± 0.09
a Values from Southworth et al. (2012).
b Values from Maciejewski et al. (2013).
c Values from Lendl et al. (2013).
d Values for limb darkening derived from Claret & Bloemen (2011) quadratic limb darkening
tables.
TABLE 3
Fitted Parameters From Band-Integrated Time Series
Parameters
WASP-12 b
WASP-17 b
WASP-19 b
Rp /R∗
µ1
µ2
Mid-Transit (MJD)
Slopea
0.11895 ± 0.0013
0.085 ± 0.024
0.281 ± 0.034
55663.199736 ± 0.000065
-0.00793 ± 0.00034
0.12316 ± 0.00058
0.083 ± 0.031
0.256 ± 0.046
55750.294793 ± 0.00088
-0.00578 ± 0.0010
0.14140 ± 0.00093
0.092 ± 0.025
0.305 ± 0.027
55743.532268 ± 0.000040
-0.00407 ± 0.00039
a Linear slope has units of normalized flux per day.
tions before conclusions as to its validity or physical nature can be made. The light curve for WASP-17 does
not include a post-egress portion so we cannot evaluate
the presence of a curved baseline.
WASP-12
1.002
WASP-19
Data
Flat
Sine
Poly
Normalized Flux
1.001
1.000
0.999
0.998
1.0010
1.0005
1.0000
Trans. Dep. (%)
1.44
F
1.42
1.40
1.38
Trans. Dep. (%)
2.02
0.9995
F
2.00
1.98
S
−0.10
P
1.96 S
0.9990
P
0.10 −0.10
−0.05
Time From Mid−Transit (days)
0.05
Fig. 9.— The out-of-transit portions of the band-integrated light
curves for WASP-12 (left) and WASP-19 (right), with models
including only a linear trend (red) and an additional sinusoidal
component (blue) or 2nd-order polynomial function (green) overplotted. The best-fit transit depths for each model are also plotted
(inset). The addition of sinusoidal or polynomial components produce a marginally better fit, but the improvements are not sufficient
to yield a lower BIC.
The in-transit orbit of WASP-19 also has a region just
after second contact (after the end of ingress) which deviates slightly from a standard transit curve (see Figure 10). The amplitude and duration of the deviation
is similar to the amplitude and duration of starspots detected in optical transit data by Tregloan-Reed et al.
(2013), so we experimented with including a Gaussianshaped spot in our transit model. The spot model leads
to a statistically better fit with ∆BIC = 7.8 (see Figure 10), leading us to adopt a model including a sunspot
modeled as a Gaussian with a position centered at MJD
55743.526, a relative amplitude of 0.06%, and a width of
0.0036 days. We locked the amplitude of the spot when
fitting each of the bins, since our data quality is insufficient to determine variations with wavelength. Neither
of our other data sets showed evidence for star spots,
which is expected since both WASP-17 and WASP-12
are significantly hotter than WASP-19.
Considering the ambiguity regarding the presence of
additional visit-long components and star spots, we decided to use the average of all the model fits with and
without a sinusoidal component or a spot for the bandintegrated transit depth listed in Table 3, and augment
the uncertainty values to encompass the full range of values; this increases the uncertainty by a factor of ∼4 for
WASP-19 and a factor of ∼5 for WASP-12. To remove
these ambiguities in the band-integrated transit depth we
would need a fully-sampled light curve and multiple visits
10. 10
WASP-19 Transit Models With & Without A Star Spot
2.03
Tran. Depth (%)
With Spot
2.02
2.01
No Spot
2.00
0.985
1.99
0.980
−0.03
−0.02
−0.01
0.00
Time From Mid−Transit (days)
Fig. 10.— The trough of the transit for the band-integrated light
curve for WASP-19, with models including standard transit model
(red) and a model with a star spot (blue) over-plotted. The best-fit
transit depths for each model are also plotted (inset). The value
derived incorporating the spot model has a larger uncertainty from
MCMC due to the additional free parameters, but the effects of red
noise are not included and therefore the uncertainty on the spotfree fit is underestimated.
to settle the question of spots; however, since we lock the
values for any non-linear or spot components when fitting
the bins, the final choice of the best-fit band-integrated
model makes no difference in the relative depths for our
wavelength bins.
4.4. Fitting the Spectrally Binned Light Curves
Once we determined an adequate fit to the bandintegrated light curves, we used the residuals of the fit to
remove systematics common to all spectral channels (or
bin of channels). Our transit models for each individual
channel include a constant scaling of these residuals, with
the scale factor varying as a free parameter. This strategy is similar to methods developed independently by
Deming et al. (2012) and Stevenson et al. (2013) (though
without a scaling term for modulating the amplitude of
the band-integrated residuals), and it obviates the need
for using the divide-oot method. Additionally, we introduced two more components into the light curve model
(each with a scaling factor as a free parameter) based on
our measurements of the horizontal and vertical shifts of
the spectrum on the detector over time. The scaling factors for these components are insignificant for most bins
since a small shift for most points on the spectrum will
not change the flux significantly; however, near spectral
features or near the edges of the spectrum, these shifts
can cause the flux within a single bin to drift up or down.
Our final model light curve for comparison with the data
takes the form
LCf inal = LCtransit ∗ (a + bt + C1 ∗ ResBI +
C2 ∗ Shifty + C3 ∗ Shiftx )
2.0
0.01
(2)
where LCtransit is the light curve model calculated using the Mandel & Agol (2002) prescription, a and b are
coefficients for a linear trend with time, ResBI are the
residuals from the band-integrated light curve, and the
C coefficients are scaling parameters determined through
our MCMC fitting.
1.5
WASP-12
1.0
0.5
Residual Scale Factor
Normalized Flux
0.990
Data
No Spot
Spot Included
For the light curve for each spectral bin we followed the
above methods for bad pixel and bad channel correction
and then fit for the best model using MCMC. We locked
the same parameters as with the band-integrated light
curve, and additionally locked the limb darkening and
mid transit time to the best-fit values from the bandintegrated light curve analysis; this allows us to measure
the relative change in transit depth while maintaining
the same transit shape. We experimented with fitting
for the limb darkening parameters using priors based on
a linear interpolation between the J and H-band values
from Claret & Bloemen (2011), but we determined that
there was no change in the final transit depths compared
with exclusively using the band-integrated values.
2.0
WASP-17
1.5
1.0
0.5
1.5
Peak of
Spectrum
WASP-19
1.0
0.5
1.1
1.2
1.3
1.4
1.5
Wavelength (µm)
PSF
Shape
1.6
1.7
Fig. 11.— Best-fit scaling factors for the band-integrated light
curve residuals derived for each channel (see §4.4). The relative
amplitude of the scaled-residuals component of the model changes
with wavelength based on the peak illumination in each channel,
and varies between targets based on the sub-array size and sampling mode (see Table 1). For WASP-17 the scale factor peaks at
the location of the peak flux in the spectrum, while for WASP-19
the scale factor varies based on the sampling of the spatial PSF.
WASP-12 has very little structure in the band-integrated residuals,
and therefore shows no clear correlation with flux.
In each bin the importance of the different systematic
trends varies. The amplitude of the common-mode residuals is related to (but not directly correlated with) the
peak intensity in each channel (see Figure 11), and the
x shift is only important near spectral features or other
steep gradients in the spectral direction. To avoid including unnecessary components in our light curve model, we
examined the importance and validity of including each
model parameter using a nested model selection analysis. We began by assuming that the values determined for
the band-integrated light curve except for Rp /R∗ and the
mean value of the out-of-transit flux would be valid for
all the bins. We then calculated ∆BIC for models with
the inclusion of free parameters for the slope of the linear
trend, the scale factor for the band-integrated residuals,
and scale factors for components based on the x and y
shifts; we included only the parameters that provided an
improvement in the BIC (∆BIC ≥ 2) over the model that
11. 11
Δ BIC Values for Model Selection
20
Δ BIC
15
10
5
Residuals Scaling
Slope
X Shifts
Y Shifts
WASP-12
1.8
1.6
OOT Flux
WASP-12
0.121
0.120
0.119
0.8
0.118
0.6
0.10
0.117
WASP-17 0.126
Y Shift
0.05
0.124
0.00
0.122
-0.05
0.120
X Shift
WASP-19 0.144
0.0002
0.143
0.142
0.0000
-0.0002
50
WASP-17
40
10
0
WASP-19
10
5
0
-5
-10
1.1
1.2
1.3
1.4
Wavelength (µm)
0.140
0.139
1.0000 1.0005 1.0010
0.138
Rp/R*
Fig. 13.— Left: Correlation plots for the three model components versus Rp /R∗ , for WASP-17 (see §4.4). Parameters were
only allowed to vary for those bins in which doing so resulted in
∆BIC ≥ 2, and only the bins in which the parameters varied are
plotted; the dotted lines represent the default value from the bandintegrated results. Results for WASP-12 and WASP-19 are not
plotted because the number of bins with open parameters for each
component was small (1 − 4). Right: Best-fit out-of-transit flux
versus Rp /R∗ for all the targets. No correlation is seen between
Rp /R∗ and any of the parameters.
20
15
0.141
0.120 0.122 0.124 0.126
Rp/R*
30
0.123
0.122
1.0
-5
Δ BIC
Residuals
1.2
0
Δ BIC
WASP-17
1.4
Scaling Factor
locked that parameter. The ∆BIC values for each of our
0.027 µm-wide bins for each of our targets are shown in
Figure 12. To further confirm that we are not over-fitting
our data, we searched for correlations between different
free parameters in our light curve model and the final
transit depths. Most of the parameters in most of the
bins remain locked to the band-integrated values (the
slope of the linear trend remained locked for every bin
for all targets), and we see no evidence of correlations between parameters for the fitted parameter values in any
of our targets (see Figure 13).
1.5
1.6
1.7
Fig. 12.— We calculate the change in BIC values for a model
that fits for additional systematic trends (band-integrated residuals, the visit-long linear slope, x shift, y shift) compared with the
default model (see §4.4). ∆BIC is shown for each of the 19 bins,
for all targets (top: WASP-12, middle: WASP-17, bottom: WASP19). The horizontal red line at zero indicates the level above which
parameters are said to be significant — parameters are only allowed to vary from the best-fit band-integrated values if they have
∆BIC ≥ 2.
In Figure 14 we show final light curves for all of our
0.027 µm-wide bins for each target after the various bestfit systematic trend components have been removed;
they are overplotted with the best-fit transit light curve
model. The light curves show no sign of correlated noise,
and the posterior distributions (shown in Figure 15) are
all fit well by a Gaussian distribution. Our final spectra
for each of our science targets are shown in Figure 16; we
plot the best-fit transit depth values for each individual
channel, and two bin sizes (0.027 µm and 0.1 µm). The
individual channels clearly show a high point-to-point
scatter which appears to be largely due to photon noise,
so we experimented with binning the channels using sequential bin sizes (2 channels, 3 channels, etc). The rms
of the resulting spectra drops off quickly, but then stays
elevated above the photon-noise limit for all stars beyond a 5-channel bin width, suggesting structure in the
spectrum on scales larger than 5 pixels (see Figure 17).
We therefore chose to use the 6-channel bins (0.027 µm)
for our final spectrum, since they will largely conserve
the overall structure of the individual-channel spectrum
while decreasing the photon noise considerably and allowing for improved removal of systematic trends. Larger
bin sizes, as used by Stevenson et al. (2013) and (Huitson et al. 2013), do not fully encapsulate the structure
in the smaller-bin spectrum. This smoothing is not incorporated into the uncertainty limits for the wider bins
since the uncertainty is purely based on the goodnessof-fit of the transit model; we therefore believe the use
of bin sizes < 0.03 µm is necessary to avoid misinterpretation of spectral characteristics. The best-fit transit
depths for the 0.027 µm-wide bins for all of our targets
are listed in Table 4.
4.5. Uncertainty Analysis
The uncertainty limits for our light curve parameters
were derived from the widths of our MCMC posterior
probability distributions; however, the uneven sampling
before and after a transit as well as across a transit event
due to the gaps in the HST orbit make the calculation of
the expected noise limit difficult. We therefore decided
to construct synthetic data sets for each of our targets
12. 12
Fig. 14.— The final results for all the bins for each target are shown in black, after removing time series components based on the scaled
residuals from the band-integrated light curve, as well as any scaled components based on the spectral shift in the x and y directions that
were deemed statistically significant (see §4.4). The best-fit transit model from our MCMC analysis is shown in blue. The light curves all
show essentially white noise, with no evidence of correlated noise or remaining systematic trends.
in order to identify the different contributing sources of
uncertainty in the final results, with each synthetic data
set for an exoplanet constructed using the best-fit parameters from the fit to our band-integrated light curve
and the timing array of our real data. Stochastic Gaussian noise was injected at the level of the final rms determined for our data, and the synthetic data was fit
using MCMC in the same method described above for
the real light curves. Since each data set has a relatively
small number of data points (131 for WASP-17, 274 for
WASP-19, and 484 for WASP-12), the impact of outliers
due to purely stochastic noise can have a considerable effect, so we repeated this process 100 times with different
randomly generated noise distributions in order to de-
termine the range of uncertainties produced by MCMC.
We can then compare the predicted noise based on the
number of points in transit to the predicted uncertainty
from MCMC fits to the synthetic data to estimate the increase in uncertainty due to the uneven sampling of the
light curves. Also, by comparing the uncertainty derived
for our real data to the range of uncertainties for the
simulated data sets we can estimate the amount of additional (red) noise in our data compared with a purely
(white) stochastic noise distribution.
We also explored the use of residual-permutation analysis (RP) to estimate the effects of red noise. We fit the
light curves using Levenberg–Marquardt least-squares
fitting, subtracted the best fit model from the light curve,
13. 13
WASP-12
1.14
µm
1.17
µm
1.20
WASP-17
WASP-19
1.13 µm
1.12 µm
1.16 µm
1.15 µm
µm
1.18 µm
1.17 µm
1.23
µm
1.21 µm
1.20 µm
1.25
µm
1.24 µm
1.23 µm
1.28
µm
1.27 µm
1.26 µm
1.31
µm
1.30 µm
1.29 µm
1.33
µm
1.32 µm
1.31 µm
1.36
µm
1.35 µm
1.39
µm
1.38 µm
1.42
µm
1.41 µm
1.44
µm
1.44 µm
1.47
µm
1.47 µm
1.50
µm
1.49 µm
1.52
µm
1.52 µm
1.55
µm
1.55 µm
1.58
µm
1.58 µm
1.61
µm
1.61 µm
1.63
µm
1.63 µm
0.116
0.118
0.120
Rp/R*
0.122
0.120
1.34 µm
1.37 µm
1.40 µm
1.43 µm
1.46 µm
1.48 µm
1.51 µm
1.54 µm
1.57 µm
1.60 µm
1.62 µm
0.122
0.124
Rp/R*
0.126
0.140
0.142
Rp/R*
0.144
Fig. 15.— Posterior distributions from MCMC for Rp /R∗ for every bin, for each of the three targets. All of the final distributions are
symmetric and well-approximated by a Gaussian fit (red).
shifted the residuals by one position and then added the
model back in and re-fit the data, cycling through all
the data points in each light curve. However, we found
that with such a small number of data points in our light
curves and the uneven sampling of the HST orbits the
RP method is not sufficiently robust; the final distributions for the fitted values of Rp /R∗ showed a large scatter without any clear pattern. We therefore relied on our
simulated data tests to determine how close we came to
the expected photon noise.
The band-integrated photon noise statistics, rms uncertainty, and uncertainties in transit depth determined
from MCMC fitting for the real and synthetic data sets
are shown in Table 5. We find that the rms of the data is
1.2−1.44× the expected photon noise for band-integrated
time series, but only 1.11 − 1.22× the photon noise limit
for the binned data. For WASP-12 the MCMC results
for the synthetic data match within a few percent to
the predicted uncertainties based on the rms, suggesting
that the impact of light curve sampling is minimal. The
real band-integrated data for WASP-12 are slightly noisier than the synthetic data suggesting some correlated
noise, most likely due to trends in the out-of-transit portion of the data discussed previously §4.3.1. The WASP19 results are similar, though the MCMC uncertainties
and the dispersion in the range of value for the synthetic
data are larger than predicted due to the impact of fitting for the presence of a spot (§4.3.1). For WASP-17
the uncertainty for the synthetic data is more than 2×
larger than the predicted uncertainty due to the lack of
data covering ingress/egress or post-transit. However,
we note that the effects of sampling and correlated noise
are almost completely neutralized in the binned data by
our residual subtraction - the ratio of the uncertainty
for the simulated data to the analytical prediction for all
the targets drops to essentially unity, demonstrating the
effectiveness of our component removal method.
5. DISCUSSION
The observations analyzed in this study represent a
preliminary sample of hot exoplanets observed with the
WFC3 instrument on HST. The three planets include
two extremely hot planets with temperature structures
constrained by Spitzer occultation data (WASP-12 b and
WASP-19 b) as well as a cooler planet with a highlyinflated planetary radius (WASP-17 b), allowing us to
investigate two classes of planets that pose significant
challenges for current theories of exoplanet structure and
evolution.
5.1. Comparison with Atmospheric Models
Absorption band depths in transit spectra probe the
line of sight through the terminator of the planet, and are
14. 14
TABLE 4
Derived Transit Depths For Binned Data
λ (µm)
1.145
1.172
1.199
1.226
1.253
1.281
1.308
1.335
1.362
1.389
1.416
1.443
1.471
1.498
1.524
1.552
1.579
1.606
1.633
WASP-12 b
Transit Depth (%)
1.4131
1.4211
1.4302
1.4417
1.4376
1.4103
1.4143
1.4387
1.4338
1.4419
1.4414
1.4322
1.4505
1.4719
1.4645
1.4707
1.4170
1.4264
1.4073
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
λ (µm)
0.0235
0.0232
0.0224
0.0226
0.0224
0.0230
0.0207
0.0190
0.0186
0.0225
0.0207
0.0217
0.0237
0.0231
0.0229
0.0286
0.0296
0.0329
0.0400
WASP-17 b
Transit Depth (%)
1.128
1.156
1.184
1.212
1.240
1.268
1.296
1.325
1.353
1.381
1.409
1.437
1.465
1.493
1.521
1.549
1.577
1.606
1.634
1.5087
1.4867
1.5044
1.4957
1.4998
1.5166
1.4822
1.5362
1.5545
1.5686
1.5050
1.5578
1.5446
1.5300
1.5086
1.5410
1.5534
1.4875
1.4530
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
0.0257
0.0250
0.0259
0.0216
0.0222
0.0226
0.0237
0.0197
0.0223
0.0239
0.0261
0.0250
0.0267
0.0247
0.0229
0.0316
0.0282
0.0278
0.0303
WASP-12
λ (µm)
1.118
1.146
1.174
1.202
1.230
1.258
1.286
1.314
1.343
1.371
1.399
1.427
1.455
1.483
1.511
1.539
1.568
1.597
1.624
WASP-19 b
Transit Depth (%)
2.0159
2.0241
1.9905
2.0071
1.9269
1.9880
1.9941
2.0176
1.9943
2.0318
2.0317
2.0546
2.0363
1.9923
2.0470
2.0053
2.0350
2.0578
2.0142
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
0.0175
0.0206
0.0172
0.0180
0.0189
0.0180
0.0187
0.0151
0.0174
0.0168
0.0157
0.0176
0.0171
0.0196
0.0187
0.0205
0.0196
0.0197
0.0188
Standard Deviation vs Bin Size
0.8
WASP-12
WASP-17
WASP-19
Normalized Std. Dev.
1.5
1.4
Transit Depth (%)
1.3
1.7
WASP-17
0.6
0.4
0.2
1.6
0.0
0
1.5
1.4
2.1
2.0
1.9
1.2
10
0.05 µm
(11 pix) Bins
0.1 µm
(22 pix) Bins
Photon-noise
Limit
20
30
40
Bin Width (# of Channels)
50
60
Fig. 17.— After fitting for the transit depths using individual
channels, we binned the spectra using bin sizes between 2 and 55
points and then calculated the standard deviation of each binned
spectrum; the results for each star are plotted as well as the expected relationship based on photon-noise statistics alone. The
standard deviation for all the targets is approximately photonlimited up to 5-channel bins, but then levels off. We use a 6-channel
bin size for our final results; spectra using both the 6-channel bins
and 22-channel (0.1 µm) bins are shown in Figure 16 for comparison.
WASP-19
1.1
0.027 µm
(6 pix) Bins
1.3
1.4
1.5
Wavelength (μm)
1.6
1.7
Fig. 16.— Final spectra for each of our targets. The individual
channel depths are shown in grey, with the results for 0.027 µmwide (blue) and 0.1 µm-wide (red) bins overplotted. The differences between the channels and the 0.027 µm-wide bins are consistent with photon-noise variations, but the 0.1 µm-wide bins appear to remove structure in the spectra that could be significant;
we therefore chose to use the 0.027 µm-wide bins in our analysis.
primarily sensitive to a combination of the atmospheric
composition and the scale heights over which each species
is absorbing. These factors can be significantly degenerate and it is difficult to place strong constraints on the
overall abundances of different species with observations
in only a single wavelength band. We therefore reserve a
detailed examination of constraints on atmospheric composition and structure to a later study, and restrict our
current analysis to a discussion of the general implications of qualitative comparison with several different sets
of models.
In Figure 18 we plot the data for each planet and overplot two different sets of models, which utilize different
strategies for constraining the atmospheric structure and
composition. One set (top in Figure 18) is based on the
framework of Burrows et al. (2000) and more recently
15. 15
TABLE 5
Uncertainty Analysis
Parameters
Data points during transit
Data points out of transit
WASP-12
WASP-17
WASP-19
196
288
54
77
70
204
Band Integrated Time Series
Photon noise (ppm)
RMS of residuals (ppm)
357
515
279
350
255
305
Predicted1 σtd (ppm)
σtd from MCMC, Data
σtd from MCMC, Sim.2
52
53
53±2
67
144
145±13
45
65
63±11
1.44
1.02
1.03±0.04
1.26
2.15
2.16±0.19
1.20
1.44
1.40±0.24
RMS/photon noise
Data/Pred.
Sim./Pred.
0.027 µm Bin Width (19 Total)
Photon noise (ppm)
RMS of residuals (ppm)
1560
1880
1220
1400
1110
1230
Predicted1 σtd (ppm)
σtd from MCMC, Data
σtd from MCMC, Sim.2
174
180
181±6
249
257
242±14
170
180
187±11
1.22
1.02
1.03±0.03
1.15
1.03
0.97±0.06
1.11
1.06
1.1±0.06
RMS/photon noise
Data/Pred.
Sim./Pred.
1 Calculated from the residual rms and the number of points during
transit and out of transit
2 Simulated data was created with a sampling equivalent to that of
the real data, and an rms equivalent to the rms of the final residuals.
Burrows et al. (2006), Burrows et al. (2008) and Howe
& Burrows (2012). The Burrows models calculate the
chemical and radiative equilibrium state of each planet
based on the mass, size, and incident radiation, assuming solar abundances; the spectra were then calculated
by combining day- and night-side model atmospheres
joined at the terminator. Adjustments were made to
the abundance of important molecular absorbers such as
H2 O, CH4 and CO and/or the inclusion of additional
absorbers that affect the temperature structure and/or
broadband optical depth of the atmosphere with the goal
of improving fits to multi-wavelength observations. For
example, additional opacity at optical wavelengths is required to produce a thermal inversion postulated to explain Spitzer/IRAC photometric measurements during
occultation for a number of planets including WASP-12
b (Cowan et al. 2012; Crossfield et al. 2012) and possibly WASP-19 b (Anderson et al. 2013). TiO has been
considered as the most likely candidate (Hubeny et al.
2003; Fortney et al. 2008), but the lifetime for TiO in the
upper atmosphere may be problematic for this hypothesis (Spiegel et al. 2009) and recent searches for spectral
features of TiO have been unsuccessful (Huitson et al.
2013). On the other hand, a haze or dust with opacity through the optical and NIR is required to fit measurements of molecular absorption features for several
hot Jupiters (Charbonneau et al. 2002; Pont et al. 2013;
Deming et al. 2013). While the physical nature of these
absorbers is currently unclear, we can test how different
opacities for these parameters affect the model spectra
in our wavelength region.
The Burrows models, which are characterized by broad
H2 O absorption at 1.4 µm that slopes consistently down-
ward towards longer wavelengths, fit the data for WASP17 b reasonably well — both a standard model and an
isothermal model with haze yield a lower BIC (assuming
3 degrees of freedom) than simply fitting a line to the
data (2 degrees of freedom), with the best-fitting model
(the hazy model) giving a ∆χ2 ∼ 10. A model with
haze is required to reproduce the flat region shortwards
of 1.3 µm, and a haze hypothesis may gain additional
support from the fact that the best fits to the models are
improved (∆χ2 < 0) in every case by including a linear
trend to the models; we discuss the implications of these
results in §5.2. However, the results for the two hotter
planets are more ambiguous. The majority of the spectrum for WASP-12 b is consistent with a flat spectrum
within the uncertainties (χ2 = 0.57), and the amplired
tude of the expected features do not allow us to discriminate between standard models with either an equilibrium
temperature structure, an isothermal temperature structure suggested by Crossfield et al. (2012), or a model with
a deficit of water and enhanced carbon abundance that
best fits the analysis of Spitzer/IRAC occultation results
by Cowan et al. (2012). WASP-12 b and possibly WASP17 b also appear to have additional absorption in the region from 1.5 − 1.6 µm; these features are several bins
wide, and do not appear to be the result of random noise.
For WASP-19 b the results are even less consistent with
the models - none of the models yield an improvement
in BIC or χ2 over a linear fit. The spectrum shows an
increase in absorption beyond 1.35 µm suggestive of H2 O
but does not include the consistent drop at longer wavelengths expected from the models and apparent in the
WASP-17 b spectrum; additionally, several bins in this
region show a steep drop in absorption compared with
the smooth downward trend expected from the Burrows
models.
The second set of models we compare to our data (bottom in Figure 18) are based on the framework of Madhusudhan & Seager (2009) and Madhusudhan (2012),
which relax the stringent requirements for radiative and
chemical equilibrium in favor of flexibility when exploring
the constraints on parameter space from available observations. In particular, the Madhusudhan models explore
a range of carbon-to-oxygen (C/O) ratios for the overall
composition of the atmosphere, and include a number
of less abundant carbon-bearing species that may produce additional absorption features in NIR spectra at
C/O≥ 1. The models plotted roughly correspond to either an oxygen-rich chemistry (C/O ∼ 0.5, i.e. essentially the solar value) or a carbon-rich chemistry (C/O
>1) for specific temperature profiles (see Madhusudhan
∼
(2012) for details). It is clear that there are a number of
overlapping spectral features that lead to degeneracies the H2 O feature at 1.4 µm overlaps with CH4 at 1.36 µm
and HCN at 1.42 µm-1.51 µm, while the H2 O feature at
1.15 µm overlaps with CH4 . The oxygen-rich and carbonrich models primarily diverge between 1.45 and 1.65 µm,
where the carbon-rich models include features from HCN
and C2 H2 ; while the additional absorption in WASP-17
b and WASP-19 b appears to line up well with these
features and produces an improvement in χ2 , the uncertainties in both our data and the range of potential
model parameter values are large enough that we cannot
discriminate between oxygen-rich and carbon-rich com-
16. 16
WASP-12 b
WASP-19 b
1.60
1.46
2.05
1.55
1.44
1.50
1.42
2.00
1.45
1.40
Transit Depth (%)
WASP-17 b
1.65
Models based on
1.48 Burrows et al. 2008
1.38
Solar + TiO
Solar & Isoth., T = 2500 K
0.1 H2O, 10x carbon
1.36
1.65
Models based on
1.48 Madhusudhan 2012
1.95
Solar, no TiO
Solar & Isoth, T = 2000 K
Solar & Isoth. + haze
1.40
1.90
1.60
1.46
2.05
1.55
1.44
1.42
1.50
1.40
1.45
1.38
1.36
1.1
1.2
1.3
1.4
1.5
1.6
2.00
1.95
1.40
O-Rich (C/O = 0.5)
C-Rich (C/O = 1.5)
1.7
1.1
Solar + TiO
Solar & Isoth., T = 2500 K
Solar & Isoth. + haze
Solar + Broadband Opt. Abs.
O-Rich (C/O = 0.5)
C-Rich (C/O = 1.5)
1.2
1.3
1.4
1.5
Wavelength (µm)
1.6
1.7
1.90
1.1
O-Rich (C/O = 0.5)
C-Rich (C/O = 1)
C-Rich, low CH4
1.2
1.3
1.4
1.5
1.6
1.7
Fig. 18.— Transit depths for each of the 19 bins for each target, with models based on the framework of Burrows et al. (top) and
Madhusudhan et al. (bottom). Standard models from Burrows et al. provide a good fit for WASP-17 b and a reasonable fit for WASP-12
b, but for WASP-19 b the models do not fit well beyond 1.45 µm. Models with a deep water absorption feature can also be adjusted to
fit the data by adding an absorbing haze layer with an opacity of 0.01 cm2 /g; the hazy model for WASP-17 b is further supported by the
linear slope that is needed to match the models to the data. The oxygen-rich and carbon-rich models by Madhusudhan et al. fit equally
well for WASP-12 band WASP-17 b, but for WASP-19 b the carbon-rich models provide a statistically better fit than the oxygen-rich
models. However, except for WASP-17 b the data is fit almost equally well by a flat spectrum, though WASP-19 b would require a very
large scatter between the data points.
positions based on these data alone.
We conclude that the data for all our targets are consistent for the most part with standard atmospheric models,
but further improvements in S/N and a more comprehensive modeling strategy incorporating additional constraints on the molecular abundances and temperatures
from other data sets are necessary to discriminate between them. In particular, the origin of significant deviations from the standard solar composition model predictions at wavelengths beyond 1.5 µm is unclear; these
features could either be indicative of unexpected atmospheric absorption features or they could be unexplained
artifacts in the data. We have examined all of our data
analysis routines in detail and we have found no obvious
problems with the analysis of these bins, but repeated
observations are necessary to confirm that the results
are robust. We also point out the importance of using
bins appropriately sized to be sensitive to the possibility of narrower spectral features in the data; Figure 16
demonstrates that using bin sizes larger than ∼ 0.03 µm
smoothes the data significantly and has the potential
to erase the signatures of small-scale fluctuations in the
data.
5.2. Comparison to Previous Results
5.2.1. WASP-12
As mentioned previously, the data set that we analyzed for WASP-12 was originally observed and analyzed
by Swain et al. (2013), and the data set has also recently been analyzed as part of a multi-wavelength study
by Stevenson et al. (2013). Figure 19 shows our final spectrum for WASP-12 binned to match Stevenson
et al. (2013) and plotted with the results from these
two studies. While it is always difficult to pin-point
differences between independent analyses, there are two
possible sources of significant variations between the results of the three different studies: the technique for fitting or modeling the flux from the nearby contaminating
source, and the details of fitting the transit light curve
model. Stevenson et al. (2013) demonstrated that by
using two different transit modeling methods, small differences could be introduced in the spectrum; similarly,
we have shown in §4.2 that the choice of the spectrum
for the contaminating flux from WASP-12 BC can change
the fitted transit depths by a factor comparable to the
fitting uncertainty.
Remarkably, all the spectra show similar trends at
wavelength longer than 1.2 µm, with a high point at
1.225 µm and a broad peak from 1.325−1.575 µm. There
are slight differences (at the 1 − 2σ level) for the bins at
1.425 and 1.525 µm, but the major disagreement is at
the short-wavelength edge of the spectrum - the Swain
et al. results show a steady rise at short wavelengths
while the Stevenson et al. results show a upward spike
in the shortest-wavelength bin (1.125 µm), in contrast
our spectrum which shows a drop shortwards of 1.2 µm.
This region of the spectrum is particularly susceptible
to the choice of the dilution factor for the contaminating star due to the wavelength shift of the spectrum (see
Figure 7), and the edges of the spectrum also exhibit a
steep gradient in flux due to the grism sensitivity which
can lead to systematic trends if the spectrum drifts over
time (see §4.1); we therefore believe that a careful treatment of this spectral region is imperative. The down-
17. 17
ward slope of our final spectrum does not require any
additional absorption from species such as TiH or CrH,
as suggested by Swain et al. (2013). Our uncertainties
are larger than those of Stevenson et al. (2013), but we
believe the larger uncertainties are warranted based on
the uncertainty in the contribution from WASP-12 BC.
WASP-12 Comparison
1.65
Swain et al. 2013
Stevenson et al. 2013
This work
1.50
1.60
1.45
1.40
1.2
1.3
1.4
1.5
Wavelength (µm)
1.6
1.7
Fig. 19.— Results from Swain et al. (2013) shown in grey, results
from Stevenson et al. (2013) shown in red, and from this work
in blue. Results from this work have been binned to the same
size and number of bins as those used by Stevenson et al. (2013),
with edge bins offset due to different choices of spectral trimming.
Results from Stevenson et al. (2013) have been shifted up slightly
for comparison. The spectra are largely consistent, with the most
noticeable offsets visible at the short edge of the spectrum.
5.2.2. WASP-17
There are no prior spectroscopic analyses of WASP-17
at H-band wavelengths, but we can compare our results
with the recent WFC3 observations of HD209458 b by
Deming et al. (2013). HD209458 b is similar in mass and
temperature to WASP-17 b, but with a much smaller
scale height - WASP-17 b has a scale height that is 3.4×
larger than HD209458 b. In Figure 20 we plot our spectrum of WASP-17 b with the spectrum of HD209458 b
from Deming et al. (2013), scaled up to compensate for
the differences in scale height between the two planets;
the spectra match very closely, though there is no evidence for the outlying peak at 1.575 µm in the spectrum of HD209458 b. The similarity between two cooler,
lower-mass planets is especially notable considering that
dissimilarity between the spectrum for WASP-17 b and
the spectra for our other two targets, which are much
hotter and more massive.
As stated earlier, we find that the models for WASP-17
b fit best when we include an additional linear slope in
the models; we calculate a change in the baseline radius
of ∼1.63×104 km across our bandpass for the best-fitting
hazy model. If we assume that this spectral slope is due
to a change in effective radius with wavelength due to
Rayleigh scattering, we can use Eqn. 4 from Lecavelier
Des Etangs et al. (2008) to compare our spectral slope to
similar results for the spectral slope of HD189733 b across
optical and IR wavelengths (Pont et al. 2008; Lecavelier
Des Etangs et al. 2008; Pont et al. 2013). WASP-17 b is
hotter than HD189733 b by ∼400K, and the gravity is
lower by a factor of ∼7; combining these factors leads to
a change in altitude across our bandpass of ∼4.65×103
km –10× larger than for HD189733 b, but still a factor of 3.5× smaller than our best-fit value. Considering
Transit Depth (%)
Transit Depth (%)
1.55
1.1
the lack of a detectable slope in the data for HD209458
b, and the size of the uncertainty bars on our data, we
consider this result highly speculative at this point; improved constraints through additional WFC3 observations and/or coincident radius measurements at other
wavelengths will be necessary to examine this question
in detail.
WASP-17 b
HD209458 b (Deming et al. 2013),
adjusted for atm. scale height
1.55
1.50
1.45
1.40
1.1
1.2
1.3
1.4
1.5
Wavelength (μm)
1.6
1.7
Fig. 20.— Results for WASP-17 b (black) compared with results
for HD209458 b from Deming et al. (2013) in red. The spectrum
for HD209458 b has been scaled to compensate for the difference
in scale height for the two planets. The spectra match very well,
suggesting commonality between the spectra for cooler, smaller
planets.
5.2.3. WASP-19
The current data set for WASP-19 was also recently
analyzed by Huitson et al. (2013). Their published results utilized a bin size that is larger than ours by a factor
of 3 (0.1 µm); they also subtracted the band-integrated
residuals from each bin, but then used the divide-oot
method on each bin separately and fit for transit depth
and a linear trend. In Figure 21 we plot our results using a bin size matched to those of Huitson et al. (2013).
The transit depths using larger bins are well matched to
the Huitson et al. (2013) results, but as noted above,
with smaller bins we see deviations from the smooth
trend that appears to match the lower-resolution results.
Huitson et al. (2013) state that they do not see any major differences beyond increased photon noise when using
smaller bin sizes; however, the changes in our spectrum
seem to be robust beyond a simple increase in photon
noise. Bean et al. (2013) also presented a recent analysis
of ground-based transit and occultation observations of
WASP-19 at H-band wavelengths. Their results covered
the region from 1.25 - 2.4 µm, with gaps near the peaks
of the water features at 1.37 and 1.9 µm. The analysis
of the transit observations yields only four broad bins
in our wavelength region, similar in width and position
to several of the wavelength bins used by Huitson et al.
(2013) and generally consistent with both the Huitson et
al. results and our own results for wide bins.
6. CONCLUSION
18. 18
WASP-19 Comparison
Transit Depth (%)
2.06
2.04
Huitson
This work
2.02
2.00
1.98
1.1
1.2
1.3
1.4
1.5
Wavelength (μm)
1.6
1.7
Fig. 21.— Results from Huitson et al. (2013) in red, with results
from this work over plotted in blue, binned to the same size, with
edges offset due to different choices of spectral binning. The spectra
are largely consistent, but comparison with our smaller bin size
suggests that the Huitson et al. (2013) may be missing statistically
significant features in the spectrum.
In this paper we present our analysis of WFC3 observations of single transits for three exoplanets (WASP-12
b, WASP-17 b and WASP-19 b). We perform a careful
analysis of the band-integrated time series for each target, revealing possible evidence of curvature in the out-oftransit data for WASP-12 and WASP-19 and evidence for
a star spot in the light curve for WASP-19. We confirm
that the repeating ramp-like or hook-like artifacts seen
in a number of observations of exoplanets with WFC3
(which we call the “buffer-ramp”) can be removed in the
band-integrated light curve using the divide-oot method
from Berta et al. (2012), but we develop an alternate
method for removing the various systematic trends in the
individual channels or bins of multiple channels that utilizes the residuals of the fit to the band-integrated light
curve as well as measurements of the vertical and horizontal shift of the spectrum on the detector over time.
We utilize a model selection strategy that relies on the
Bayesian Information Criterion to determine the significance of fitting for individual systematic components,
allowing us to identify trends due to changes in the amplitude of the buffer-ramp and the impact of spectral
shifts on the flux in individual spectral bins. We present
final transit spectra for each exoplanet using 0.027 µm
channel bins, and argue that this is the optimal bin size
for increasing S/N while avoiding any loss of spectral information that exceeds the photon-noise limit. When we
use similar binning sizes to those used in previous analyses of the data for WASP-12 (Swain et al. 2013; Stevenson
et al. 2013) and WASP-19 (Huitson et al. 2013), we can
reproduce the earlier results to within uncertainties except for the shortest-wavelength bin for WASP-12; this
discrepancy may be due to treatment of data that falls on
the steep spectral slope of the WFC3 sensitivity curve.
Our analysis demonstrates that precisions close to
the photon-noise limit are possible for measurements of
wavelength-dependent transit depths with WFC3 with
the observation of only a single transit event even for
relatively dim targets (H > 10.2). Measurements of the
absolute transit depth are fundamentally limited by our
ability to constrain parameters such as limb darkening
and mid-transit time, and the phasing of HST orbits
across the light curve has a significant impact on our final uncertainties in Rp /R∗ for our band-integrated light
curves. However, using our transit model including systematic trends, we show that the uncertainties for individual bins are not strongly affected by the light curve
sampling and depend only on the number of photons acquired in transit and out-of-transit. Future observations
of these targets that utilize the newly implemented spatial scan mode will allow for increased efficiency and improved sensitivity.
Comparison with theoretical models by Burrows et al.
(2008) and Madhusudhan (2012) strongly suggest the
presence of water absorption between 1.4 µm and 1.55 µm
in WASP-17 b, and models with the inclusion of haze fit
the data better than models without haze. For WASP-12
b and WASP-19 b the agreement with standard models
including water absorption is not as clear. In particular, the spectral region beyond 1.45 µm shows increased
absorption for all our targets beyond what is predicted
from water-rich models; carbon-rich models provide a
better match in this region, but significant discrepancies
remain. We therefore believe that firm conclusions on
atmospheric composition are impossible without more
sensitive observations and/or a full analysis of multiwavelength data at both optical and NIR wavelengths.
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