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.
The document summarizes research from images taken by the New Horizons spacecraft of Charon, Pluto's largest moon. The images reveal Charon has a reddish polar cap at its north pole. Thermal models show the pole experiences long periods of extreme cold temperatures due to Charon's high obliquity and long seasons. The researchers hypothesize that methane and other volatiles escaping from Pluto's atmosphere become cold-trapped at Charon's winter pole, where they are processed by radiation into non-volatile organic compounds that remain on the surface to form the red cap. Spectral and compositional evidence supports this mechanism of seasonal accumulation of photolyzed volatiles to explain Charon's unique polar color
Плутон светится в рентгеновском диапазонеAnatol Alizar
Chandra detected X-rays from Pluto in 2014 and 2015 observations, finding 8 photons in the 0.31-0.60 keV band. No photons were detected from 0.60-1.0 keV. Allowing for background, there was a statistically significant detection of X-rays from Pluto. Charge exchange between solar wind ions and Pluto's atmosphere can produce X-rays and may explain the detection, but the observed rate is higher than expected given New Horizons measurements of Pluto's atmosphere and solar wind conditions. The solar wind may be focused within 60,000 km of Pluto to produce the detected X-ray emission.
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.
Атмосфера Земли медленно теряет кислородAnatol Alizar
This document summarizes research on reconstructing past atmospheric oxygen (O2) levels over the past 800,000 years using O2/N2 ratios measured from ancient air bubbles trapped in ice cores from Greenland and Antarctica. The main findings are:
1) O2/N2 ratios from multiple ice cores show a consistent decline of 8.4‰ per million years over the past 800,000 years, equivalent to a 0.7% decline in atmospheric O2 levels.
2) This decline is unlikely to be explained by changes in air bubble formation processes or other non-atmospheric factors, as argon/nitrogen ratios from the same ice cores show an inconsistent increasing trend over the same
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.
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
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.
The document summarizes research from images taken by the New Horizons spacecraft of Charon, Pluto's largest moon. The images reveal Charon has a reddish polar cap at its north pole. Thermal models show the pole experiences long periods of extreme cold temperatures due to Charon's high obliquity and long seasons. The researchers hypothesize that methane and other volatiles escaping from Pluto's atmosphere become cold-trapped at Charon's winter pole, where they are processed by radiation into non-volatile organic compounds that remain on the surface to form the red cap. Spectral and compositional evidence supports this mechanism of seasonal accumulation of photolyzed volatiles to explain Charon's unique polar color
Плутон светится в рентгеновском диапазонеAnatol Alizar
Chandra detected X-rays from Pluto in 2014 and 2015 observations, finding 8 photons in the 0.31-0.60 keV band. No photons were detected from 0.60-1.0 keV. Allowing for background, there was a statistically significant detection of X-rays from Pluto. Charge exchange between solar wind ions and Pluto's atmosphere can produce X-rays and may explain the detection, but the observed rate is higher than expected given New Horizons measurements of Pluto's atmosphere and solar wind conditions. The solar wind may be focused within 60,000 km of Pluto to produce the detected X-ray emission.
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.
Атмосфера Земли медленно теряет кислородAnatol Alizar
This document summarizes research on reconstructing past atmospheric oxygen (O2) levels over the past 800,000 years using O2/N2 ratios measured from ancient air bubbles trapped in ice cores from Greenland and Antarctica. The main findings are:
1) O2/N2 ratios from multiple ice cores show a consistent decline of 8.4‰ per million years over the past 800,000 years, equivalent to a 0.7% decline in atmospheric O2 levels.
2) This decline is unlikely to be explained by changes in air bubble formation processes or other non-atmospheric factors, as argon/nitrogen ratios from the same ice cores show an inconsistent increasing trend over the same
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.
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
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.
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
On the possibility of through passage of asteroid bodies across the Earth’s a...Sérgio Sacani
We have studied the conditions of through passage of asteroids with diameters 200, 100, and
50 m, consisting of three types of materials – iron, stone, and water ice, across the Earth’s
atmosphere with a minimum trajectory altitude in the range 10–15 km. The conditions of this
passage with a subsequent exit into outer space with the preservation of a substantial fraction
of the initial mass have been found. The results obtained support our idea explaining one of the
long-standing problems of astronomy – the Tunguska phenomenon, which has not received
reasonable and comprehensive interpretations to date. We argue that the Tunguska event was
caused by an iron asteroid body, which passed through the Earth’s atmosphere and continued
to the near-solar orbit.
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 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.
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.
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
Evidence for plumes of water on Europa has previously been found using the Hubble Space Telescope using two
different observing techniques. Roth et al. found line emission from the dissociation products of water. Sparks et al.
found evidence for off-limb continuum absorption as Europa transited Jupiter. Here, we present a new transit
observation of Europa that shows a second event at the same location as a previous plume candidate from Sparks
et al., raising the possibility of a consistently active source of erupting material on Europa. This conclusion is
bolstered by comparison with a nighttime thermal image from the Galileo Photopolarimeter-Radiometer that shows
a thermal anomaly at the same location, within the uncertainties. The anomaly has the highest observed brightness
temperature on the Europa nightside. If heat flow from a subsurface liquid water reservoir causes the thermal
anomaly, its depth is ≈1.8–2 km, under simple modeling assumptions, consistent with scenarios in which a liquid
water reservoir has formed within a thick ice shell. Models that favor thin regions within the ice shell that connect
directly to the ocean, however, cannot be excluded, nor modifications to surface thermal inertia by subsurface
activity. Alternatively, vapor deposition surrounding an active vent could increase the thermal inertia of the surface
and cause the thermal anomaly. This candidate plume region may offer a promising location for an initial
characterization of Europa’s internal water and ice and for seeking evidence of Europa’s habitability.
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.
The puzzling source_in_ngc6388_a_possible_planetary_tidal_disruption_eventSérgio Sacani
Artigo descreve a descoberta da destruição de um planeta ao passar próximo a uma estrela do tipo anã branca presente dentro do aglomerado globular de estrelas NGC 6388. Para isso os astrônomos utilizaram um arsenal de telescópios.
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
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.
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.
Is there an_exoplanet_in_the_solar_systemSérgio Sacani
We investigate the prospects for the capture of the proposed Planet 9 from other
stars in the Sun’s birth cluster. Any capture scenario must satisfy three conditions:
the encounter must be more distant than ∼ 150 au to avoid perturbing the Kuiper
belt; the other star must have a wide-orbit planet (a & 100 au); the planet must be
captured onto an appropriate orbit to sculpt the orbital distribution of wide-orbit
Solar System bodies. Here we use N-body simulations to show that these criteria may
be simultaneously satisfied. In a few percent of slow close encounters in a cluster,
bodies are captured onto heliocentric, Planet 9-like orbits. During the ∼ 100 Myr
cluster phase, many stars are likely to host planets on highly-eccentric orbits with
apastron distances beyond 100 au if Neptune-sized planets are common and susceptible
to planet–planet scattering. While the existence of Planet 9 remains unproven, we
consider capture from one of the Sun’s young brethren a plausible route to explain such
an object’s orbit. Capture appears to predict a large population of Trans-Neptunian
Objects (TNOs) whose orbits are aligned with the captured planet, and we propose
that different formation mechanisms will be distinguishable based on their imprint on
the distribution of TNOs
This study analyzed transit observations of the Neptune-mass exoplanet GJ 436b taken with the Hubble Space Telescope. The transmission spectrum was found to be featureless, ruling out cloud-free hydrogen-dominated atmosphere models with high significance. The flat transmission spectrum is consistent with either an atmosphere containing high-altitude clouds located at a pressure of around 1 millibar, or a relatively hydrogen-poor atmosphere with 3% hydrogen and helium by mass. Bayesian atmospheric modeling showed that cloudy hydrogen-dominated or high-metallicity hydrogen-poor atmospheres provide the best fits to the data. Further observations are needed to distinguish between these scenarios.
Evidence for the_thermal_sunyaev-zeldovich_effect_associated_with_quasar_feed...Sérgio Sacani
Using a radio-quiet subsample of the Sloan Digital Sky Survey spectroscopic quasar
catalogue, spanning redshifts 0.5–3.5, we derive the mean millimetre and far-infrared
quasar spectral energy distributions (SEDs) via a stacking analysis of Atacama Cosmology
Telescope and Herschel-Spectral and Photometric Imaging REceiver data. We
constrain the form of the far-infrared emission and find 3σ–4σ evidence for the thermal
Sunyaev-Zel’dovich (SZ) effect, characteristic of a hot ionized gas component with
thermal energy (6.2 ± 1.7) × 1060 erg. This amount of thermal energy is greater than
expected assuming only hot gas in virial equilibrium with the dark matter haloes of
(1 − 5) × 1012h
−1M that these systems are expected to occupy, though the highest
quasar mass estimates found in the literature could explain a large fraction of this
energy. Our measurements are consistent with quasars depositing up to (14.5±3.3) τ
−1
8
per cent of their radiative energy into their circumgalactic environment if their typical
period of quasar activity is τ8 × 108 yr. For high quasar host masses, ∼ 1013h
−1M,
this percentage will be reduced. Furthermore, the uncertainty on this percentage is
only statistical and additional systematic uncertainties enter at the 40 per cent level.
The SEDs are dust dominated in all bands and we consider various models for dust
emission. While sufficiently complex dust models can obviate the SZ effect, the SZ
interpretation remains favoured at the 3σ–4σ level for most models.
The nonmagnetic nucleus_of_comet_67_p_churyumov_gerasimenkoSérgio Sacani
Artigo descreve como a sonda Rosetta e o módulo Philae descobriram que o cometa Churyumov-Gerasimenko não é magnetizado, contrariando uma teoria da formação do Sistema Solar.
Cassini finds molecular hydrogen in the Enceladus plume: Evidence for hydroth...Sérgio Sacani
Saturn’s moon Enceladus has an ice-covered ocean; a plume of material erupts from
cracks in the ice. The plume contains chemical signatures of water-rock interaction
between the ocean and a rocky core.We used the Ion Neutral Mass Spectrometer onboard
the Cassini spacecraft to detect molecular hydrogen in the plume. By using the instrument’s
open-source mode, background processes of hydrogen production in the instrument were
minimized and quantified, enabling the identification of a statistically significant signal of
hydrogen native to Enceladus.We find that the most plausible source of this hydrogen is
ongoing hydrothermal reactions of rock containing reduced minerals and organic materials.
The relatively high hydrogen abundance in the plume signals thermodynamic disequilibrium
that favors the formation of methane from CO2 in Enceladus’ ocean.
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,
1) Researchers observed 15 transits of the exoplanet GJ 1214b using the Hubble Space Telescope to measure its transmission spectrum from 1.1 to 1.7 microns.
2) The transmission spectrum was featureless, inconsistent with cloud-free atmospheres dominated by water, methane, carbon monoxide, nitrogen, or carbon dioxide.
3) The most likely explanation for the featureless spectrum is the presence of high-altitude clouds in the planet's atmosphere, which block the transmission of stellar light through the lower atmosphere.
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.
Large scale mass_distribution_in_the_illustris_simulationSérgio Sacani
Observations at low redshifts thus far fail to account for all of the baryons expected in the
Universe according to cosmological constraints. A large fraction of the baryons presumably
resides in a thin and warm–hot medium between the galaxies, where they are difficult to observe
due to their low densities and high temperatures. Cosmological simulations of structure
formation can be used to verify this picture and provide quantitative predictions for the distribution
of mass in different large-scale structure components. Here we study the distribution
of baryons and dark matter at different epochs using data from the Illustris simulation. We
identify regions of different dark matter density with the primary constituents of large-scale
structure, allowing us to measure mass and volume of haloes, filaments and voids. At redshift
zero, we find that 49 per cent of the dark matter and 23 per cent of the baryons are within
haloes more massive than the resolution limit of 2 × 108 M⊙. The filaments of the cosmic
web host a further 45 per cent of the dark matter and 46 per cent of the baryons. The remaining
31 per cent of the baryons reside in voids. The majority of these baryons have been transported
there through active galactic nuclei feedback. We note that the feedback model of Illustris
is too strong for heavy haloes, therefore it is likely that we are overestimating this amount.
Categorizing the baryons according to their density and temperature, we find that 17.8 per cent
of them are in a condensed state, 21.6 per cent are present as cold, diffuse gas, and 53.9 per cent
are found in the state of a warm–hot intergalactic medium.
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
On the possibility of through passage of asteroid bodies across the Earth’s a...Sérgio Sacani
We have studied the conditions of through passage of asteroids with diameters 200, 100, and
50 m, consisting of three types of materials – iron, stone, and water ice, across the Earth’s
atmosphere with a minimum trajectory altitude in the range 10–15 km. The conditions of this
passage with a subsequent exit into outer space with the preservation of a substantial fraction
of the initial mass have been found. The results obtained support our idea explaining one of the
long-standing problems of astronomy – the Tunguska phenomenon, which has not received
reasonable and comprehensive interpretations to date. We argue that the Tunguska event was
caused by an iron asteroid body, which passed through the Earth’s atmosphere and continued
to the near-solar orbit.
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 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.
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.
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
Evidence for plumes of water on Europa has previously been found using the Hubble Space Telescope using two
different observing techniques. Roth et al. found line emission from the dissociation products of water. Sparks et al.
found evidence for off-limb continuum absorption as Europa transited Jupiter. Here, we present a new transit
observation of Europa that shows a second event at the same location as a previous plume candidate from Sparks
et al., raising the possibility of a consistently active source of erupting material on Europa. This conclusion is
bolstered by comparison with a nighttime thermal image from the Galileo Photopolarimeter-Radiometer that shows
a thermal anomaly at the same location, within the uncertainties. The anomaly has the highest observed brightness
temperature on the Europa nightside. If heat flow from a subsurface liquid water reservoir causes the thermal
anomaly, its depth is ≈1.8–2 km, under simple modeling assumptions, consistent with scenarios in which a liquid
water reservoir has formed within a thick ice shell. Models that favor thin regions within the ice shell that connect
directly to the ocean, however, cannot be excluded, nor modifications to surface thermal inertia by subsurface
activity. Alternatively, vapor deposition surrounding an active vent could increase the thermal inertia of the surface
and cause the thermal anomaly. This candidate plume region may offer a promising location for an initial
characterization of Europa’s internal water and ice and for seeking evidence of Europa’s habitability.
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.
The puzzling source_in_ngc6388_a_possible_planetary_tidal_disruption_eventSérgio Sacani
Artigo descreve a descoberta da destruição de um planeta ao passar próximo a uma estrela do tipo anã branca presente dentro do aglomerado globular de estrelas NGC 6388. Para isso os astrônomos utilizaram um arsenal de telescópios.
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
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.
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.
Is there an_exoplanet_in_the_solar_systemSérgio Sacani
We investigate the prospects for the capture of the proposed Planet 9 from other
stars in the Sun’s birth cluster. Any capture scenario must satisfy three conditions:
the encounter must be more distant than ∼ 150 au to avoid perturbing the Kuiper
belt; the other star must have a wide-orbit planet (a & 100 au); the planet must be
captured onto an appropriate orbit to sculpt the orbital distribution of wide-orbit
Solar System bodies. Here we use N-body simulations to show that these criteria may
be simultaneously satisfied. In a few percent of slow close encounters in a cluster,
bodies are captured onto heliocentric, Planet 9-like orbits. During the ∼ 100 Myr
cluster phase, many stars are likely to host planets on highly-eccentric orbits with
apastron distances beyond 100 au if Neptune-sized planets are common and susceptible
to planet–planet scattering. While the existence of Planet 9 remains unproven, we
consider capture from one of the Sun’s young brethren a plausible route to explain such
an object’s orbit. Capture appears to predict a large population of Trans-Neptunian
Objects (TNOs) whose orbits are aligned with the captured planet, and we propose
that different formation mechanisms will be distinguishable based on their imprint on
the distribution of TNOs
This study analyzed transit observations of the Neptune-mass exoplanet GJ 436b taken with the Hubble Space Telescope. The transmission spectrum was found to be featureless, ruling out cloud-free hydrogen-dominated atmosphere models with high significance. The flat transmission spectrum is consistent with either an atmosphere containing high-altitude clouds located at a pressure of around 1 millibar, or a relatively hydrogen-poor atmosphere with 3% hydrogen and helium by mass. Bayesian atmospheric modeling showed that cloudy hydrogen-dominated or high-metallicity hydrogen-poor atmospheres provide the best fits to the data. Further observations are needed to distinguish between these scenarios.
Evidence for the_thermal_sunyaev-zeldovich_effect_associated_with_quasar_feed...Sérgio Sacani
Using a radio-quiet subsample of the Sloan Digital Sky Survey spectroscopic quasar
catalogue, spanning redshifts 0.5–3.5, we derive the mean millimetre and far-infrared
quasar spectral energy distributions (SEDs) via a stacking analysis of Atacama Cosmology
Telescope and Herschel-Spectral and Photometric Imaging REceiver data. We
constrain the form of the far-infrared emission and find 3σ–4σ evidence for the thermal
Sunyaev-Zel’dovich (SZ) effect, characteristic of a hot ionized gas component with
thermal energy (6.2 ± 1.7) × 1060 erg. This amount of thermal energy is greater than
expected assuming only hot gas in virial equilibrium with the dark matter haloes of
(1 − 5) × 1012h
−1M that these systems are expected to occupy, though the highest
quasar mass estimates found in the literature could explain a large fraction of this
energy. Our measurements are consistent with quasars depositing up to (14.5±3.3) τ
−1
8
per cent of their radiative energy into their circumgalactic environment if their typical
period of quasar activity is τ8 × 108 yr. For high quasar host masses, ∼ 1013h
−1M,
this percentage will be reduced. Furthermore, the uncertainty on this percentage is
only statistical and additional systematic uncertainties enter at the 40 per cent level.
The SEDs are dust dominated in all bands and we consider various models for dust
emission. While sufficiently complex dust models can obviate the SZ effect, the SZ
interpretation remains favoured at the 3σ–4σ level for most models.
The nonmagnetic nucleus_of_comet_67_p_churyumov_gerasimenkoSérgio Sacani
Artigo descreve como a sonda Rosetta e o módulo Philae descobriram que o cometa Churyumov-Gerasimenko não é magnetizado, contrariando uma teoria da formação do Sistema Solar.
Cassini finds molecular hydrogen in the Enceladus plume: Evidence for hydroth...Sérgio Sacani
Saturn’s moon Enceladus has an ice-covered ocean; a plume of material erupts from
cracks in the ice. The plume contains chemical signatures of water-rock interaction
between the ocean and a rocky core.We used the Ion Neutral Mass Spectrometer onboard
the Cassini spacecraft to detect molecular hydrogen in the plume. By using the instrument’s
open-source mode, background processes of hydrogen production in the instrument were
minimized and quantified, enabling the identification of a statistically significant signal of
hydrogen native to Enceladus.We find that the most plausible source of this hydrogen is
ongoing hydrothermal reactions of rock containing reduced minerals and organic materials.
The relatively high hydrogen abundance in the plume signals thermodynamic disequilibrium
that favors the formation of methane from CO2 in Enceladus’ ocean.
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,
1) Researchers observed 15 transits of the exoplanet GJ 1214b using the Hubble Space Telescope to measure its transmission spectrum from 1.1 to 1.7 microns.
2) The transmission spectrum was featureless, inconsistent with cloud-free atmospheres dominated by water, methane, carbon monoxide, nitrogen, or carbon dioxide.
3) The most likely explanation for the featureless spectrum is the presence of high-altitude clouds in the planet's atmosphere, which block the transmission of stellar light through the lower atmosphere.
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.
Large scale mass_distribution_in_the_illustris_simulationSérgio Sacani
Observations at low redshifts thus far fail to account for all of the baryons expected in the
Universe according to cosmological constraints. A large fraction of the baryons presumably
resides in a thin and warm–hot medium between the galaxies, where they are difficult to observe
due to their low densities and high temperatures. Cosmological simulations of structure
formation can be used to verify this picture and provide quantitative predictions for the distribution
of mass in different large-scale structure components. Here we study the distribution
of baryons and dark matter at different epochs using data from the Illustris simulation. We
identify regions of different dark matter density with the primary constituents of large-scale
structure, allowing us to measure mass and volume of haloes, filaments and voids. At redshift
zero, we find that 49 per cent of the dark matter and 23 per cent of the baryons are within
haloes more massive than the resolution limit of 2 × 108 M⊙. The filaments of the cosmic
web host a further 45 per cent of the dark matter and 46 per cent of the baryons. The remaining
31 per cent of the baryons reside in voids. The majority of these baryons have been transported
there through active galactic nuclei feedback. We note that the feedback model of Illustris
is too strong for heavy haloes, therefore it is likely that we are overestimating this amount.
Categorizing the baryons according to their density and temperature, we find that 17.8 per cent
of them are in a condensed state, 21.6 per cent are present as cold, diffuse gas, and 53.9 per cent
are found in the state of a warm–hot intergalactic medium.
One tenth solar_abundances_along_the_body_of-the_streamSérgio Sacani
This document summarizes a study that analyzed spectra from four background quasars to measure the chemical abundances along the Magellanic Stream. Two key findings are:
1) The sightlines toward RBS 144 and NGC 7714 yielded metallicities of around 0.1 times the solar value, indicating a uniform low abundance along the main body of the Stream. This supports models where the Stream was stripped from the SMC around 1-2.5 billion years ago when the SMC had a metallicity of around 0.1 solar.
2) A higher metallicity of around 0.5 solar was found in the inner Stream toward Fairall 9, sampling a filament traced to the LMC. This shows the bifurc
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
The xmm newton-view_of_the_central_degrees_of_the_milk_waySérgio Sacani
Novas imagens do Observatório de Raios-X XMM-Newton da ESA revelaram alguns dos processos mais intensos que acontecem no coração da nossa Via Láctea.
As fontes brilhantes e pontuais que se destacam por toda imagem indicam os sistemas estelares binários onde uma das estrelas atingiu o final de sua vida, desenvolvendo para um objeto compacto e denso – uma estrela de nêutrons ou um buraco negro.
A região central da Via Láctea também contém jovens estrelas e aglomerados estelares e algumas dessas fontes são visíveis como pontos brancos e vermelhos brilhando na imagem, que se espalha por 1000 anos-luz.
A maior parte da ação ocorre no centro, onde nuvens difusas de gás estão sendo cavadas por ventos poderosos soprados por estrelas jovens, bem como por supernovas.
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
Hot Earth or Young Venus? A nearby transiting rocky planet mysterySérgio Sacani
Venus and Earth provide astonishingly different views of the evolution of a rocky planet, raising the question of why these two rock y worlds evolv ed so differently. The recently disco v ered transiting Super-Earth LP 890-9c (TOI-4306c, SPECULOOS-2c) is a key to the question. It circles a nearby M6V star in 8.46 d. LP890-9c receives similar flux as modern Earth, which puts it very close to the inner edge of the Habitable Zone (HZ), where models differ strongly in their prediction of how long rocky planets can hold onto their water. We model the atmosphere of a hot LP890-9c at the inner edge of the HZ, where the planet could sustain several very different environments. The resulting transmission spectra differ considerably between a hot, wet exo-Earth, a steamy planet caught in a runaway greenhouse, and an exo-Venus. Distinguishing these scenarios from the planet’s spectra will provide critical new insights into the evolution of hot terrestrial planets into exo-Venus. Our model and spectra are available online as a tool to plan observations. They show that observing LP890-9c can provide key insights into the evolution of a rocky planet at the inner edge of the HZ as well as the long-term future of Earth.
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.
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.
Os astrônomos descobriram um processo único sobre como as maiores galáxias elípticas do universo continuam gerando estrelas muito tempo depois do anos de pico de nascimentos estelares. A alta resolução e a sensibilidade à radiação ultravioleta do Hubble, permitiu aos astrônomos observarem nós brilhantes de estrelas azuis, quentes, se formando juntamente com jatos de buracos negros ativos encontrados nos centros das gigantescas galáxias elípticas.
Combinando dados do Huubble com observações feitas por um conjunto de telescópios baseados tanto em Terra como no espaço, duas equipes independentes descobriram que os jatos dos buracos negros, e as estrelas recém-nascidas são todos partes de um ciclo auto-regulado. Jatos de alta energia atirados do buraco negro aquecem um halo de gás circulante, controlando a taxa com a qual o gás esfria e cai na galáxia.
“Pense no gás ao redor da galáxia como uma atmosfera”, explicou o líder do primeiro estudo, Megan Donahue, da Universidade Estadual do Michigan. “Essa atmosfera pode conter material em diferentes estados, do mesmo modo que a nossa atmosfera tem gás, nuvens e chuva. O que nós estamos vendo é um processo parecido com uma tempestade. À medida que os jatos impulsionam o gás para fora do centro da galáxia, parte do gás esfria e precipita em aglomerados frios que caem de volta para o centro da galáxia como gotas de chuvas”.
“As gotas de chuva eventualmente esfriam o suficiente para tornar-se nuvens de formação de estrelas de gás frio molecular, e a capacidade de observar no ultravioleta distante do Hubble, nos permitiu observar diretamente esses chuviscos de formação de estrelas”, explicou o líder do segundo estudo, Grant Tremblay, da Universidade de Yale. “Nós sabemos que esses chuviscos estão linkados com os jatos, pois eles foram encontrados em filamentos que se dobram ao redor dos jatos, ou abraçam as bordas de bolhas gigantes que os jatos inflaram”, disse Tremblay. “E eles terminam fazendo um redemoinho de gás de formação de estrelas ao redor do buraco negro central”.
XUE: Molecular Inventory in the Inner Region of an Extremely Irradiated Proto...Sérgio Sacani
This document presents the first results from the JWST XUE program, which observed 15 protoplanetary disks in the NGC 6357 star-forming region using MIRI. For the disk XUE 1, located near massive stars, the following was found:
1) Abundant water, CO, CO2, HCN, and C2H2 were detected in the inner few AU, indicating an oxygen-dominated gas-phase chemistry similar to isolated disks.
2) Small crystalline silicate dust is present at the disk surface.
3) The column densities and chemistry are surprisingly similar to isolated disks despite the extreme radiation environment, implying inner disks can retain conditions conducive to rocky planet
Large-scale Volcanism and the Heat Death of Terrestrial WorldsSérgio Sacani
This document discusses the potential for large igneous provinces (LIPs) to cause the "heat death" of terrestrial planets through massive volcanic eruptions that overwhelm the climate system. It examines the timing of LIP events on Earth to estimate the likelihood of nearly simultaneous eruptions. Statistical analysis of Earth's LIP record finds that eruptions within 0.1-1 million years of each other are likely. Simultaneous LIPs could have driven Venus into a runaway greenhouse effect like its current state. The timing of LIP events on Earth provides insight into potential past LIP activity on Venus that may have ended its hypothesized earlier temperate climate.
Cold Molecular Gas in Merger Remnants. I. Formation of Molecular Gas DiscsGOASA
- 80% (24/30) of the merger remnants with robust CO detections showed kinematical signatures of rotating molecular gas disks (including nuclear rings) based on their velocity fields. The sizes of these disks varied significantly from 1.1 kpc to 9.3 kpc.
- In 54% of the sources, the size of the molecular gas disks was more compact than the K-band effective radius, possibly formed from past gas inflows triggered by dynamical instabilities during mergers.
- The remaining 46% had more extended gas disks relative to the stellar component, possibly forming late-type galaxies with central stellar bulges.
- The study suggests that nuclear and extended molecular gas disks are common in
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.
Predictions of the_atmospheric_composition_of_gj_1132_bSérgio Sacani
GJ 1132 b is a nearby Earth-sized exoplanet transiting an M dwarf, and is amongst the most highly
characterizable small exoplanets currently known. In this paper we study the interaction of a magma
ocean with a water-rich atmosphere on GJ 1132b and determine that it must have begun with more
than 5 wt% initial water in order to still retain a water-based atmosphere. We also determine the
amount of O2
that can build up in the atmosphere as a result of hydrogen dissociation and loss.
We find that the magma ocean absorbs at most ∼ 10% of the O2 produced, whereas more than
90% is lost to space through hydrodynamic drag. The most common outcome for GJ 1132 b from our
simulations is a tenuous atmosphere dominated by O2
, although for very large initial water abundances
atmospheres with several thousands of bars of O2
are possible. A substantial steam envelope would
indicate either the existence of an earlier H2
envelope or low XUV flux over the system’s lifetime. A
steam atmosphere would also imply the continued existence of a magma ocean on GJ 1132 b. Further
modeling is needed to study the evolution of CO2
or N2
-rich atmospheres on GJ 1132 b.
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.
The identification of_93_day_periodic_photometric_variability_for_yso_ylw_16aSérgio Sacani
This study identifies a 93 day periodic photometric variability in the Class I young stellar object (YSO) YLW 16A in the Rho Ophiuchus star forming region. Light curve analysis reveals variations of ~0.5 magnitudes in the Ks band over this period. The authors propose a triple system model consisting of an inner binary with a 93 day period eclipsed by a warped circumbinary disk, with a tertiary companion at ~40 AU responsible for warping the disk. This model is similar to one previously proposed for another YSO, WL 4, and may indicate such triple systems with eclipsing disks are common around young stars. Understanding these systems can provide insights into stellar and planetary formation and evolution.
The document summarizes observations of water in Jupiter's stratosphere made by the Herschel Space Observatory. Herschel/HIFI obtained a 5x5 pixel map of a water emission line, finding that water decreases from southern to northern latitudes. Herschel/PACS also obtained water maps. Infrared Telescope Facility observations of methane were used to constrain stratospheric temperatures. The latitudinal distribution of water cannot be explained by temperature variations and rules out interplanetary dust as the main water source. The observations provide evidence that Jupiter's stratospheric water originated from the 1994 Shoemaker-Levy 9 comet impacts.
An irradiated-Jupiter analogue hotter than the SunSérgio Sacani
Planets orbiting close to hot stars experience intense extreme-ultraviolet radiation, potentially leading to
atmosphere evaporation and to thermal dissociation of molecules. However, this extreme regime remains
mainly unexplored due to observational challenges. Only a single known ultra-hot giant planet, KELT-9b,
receives enough ultraviolet radiation for molecular dissociation, with a day-side temperature of ≈ 4, 600 K.
An alternative approach uses irradiated brown dwarfs as hot-Jupiter analogues. With atmospheres and radii
similar to those of giant planets, brown dwarfs orbiting close to hot Earth-sized white-dwarf stars can be
directly detected above the glare of the star. Here we report observations revealing an extremely irradiated
low-mass companion to the hot white dwarf WD0032−317. Our analysis indicates a day-side temperature
of ≈ 8, 000 K, and a day-to-night temperature difference of ≈ 6, 000 K. The amount of extreme-ultraviolet
radiation (with wavelengths 100−912 ˚A) received byWD0032−317B is equivalent to that received by planets
orbiting close to stars as hot as a late B-type stars, and about 5, 600 times higher than that of KELT-9b. With
a mass of ≈ 75 − 88 Jupiter masses, this near-hydrogen-burning-limit object is potentially one of the most
massive brown dwarfs known.
Similar to Spectroscopic evidence for_a_temperature_inversion_in_the_dayside_atmosphere_of_the_hot_jupiter_wasp_33b (20)
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.
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.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
The solar dynamo begins near the surfaceSérgio Sacani
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating
region of sunspot emergence appears around 30° latitude and vanishes near the
equator every 11 years (ref. 1). Moreover, longitudinal flows called torsional oscillations
closely shadow sunspot migration, undoubtedly sharing a common cause2. Contrary
to theories suggesting deep origins of these phenomena, helioseismology pinpoints
low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface
shear layer3,4. Within this zone, inwardly increasing differential rotation coupled with
a poloidal magnetic field strongly implicates the magneto-rotational instability5,6,
prominent in accretion-disk theory and observed in laboratory experiments7.
Together, these two facts prompt the general question: whether the solar dynamo is
possibly a near-surface instability. Here we report strong affirmative evidence in stark
contrast to traditional models8 focusing on the deeper tachocline. Simple analytic
estimates show that the near-surface magneto-rotational instability better explains
the spatiotemporal scales of the torsional oscillations and inferred subsurface
magnetic field amplitudes9. State-of-the-art numerical simulations corroborate these
estimates and reproduce hemispherical magnetic current helicity laws10. The dynamo
resulting from a well-understood near-surface phenomenon improves prospects
for accurate predictions of full magnetic cycles and space weather, affecting the
electromagnetic infrastructure of Earth.
Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Mat...Sérgio Sacani
In the Nice model of solar system formation, Uranus and Neptune undergo an orbital upheaval,
sweeping through a planetesimal disk. The region of the disk from which material is accreted by
the ice giants during this phase of their evolution has not previously been identified. We perform
direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid
accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment
event, with collision rates as much as ∼3 per hour assuming km-sized planetesimals, increasing the
total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the
largest total enhancement. We determine that for some plausible planetesimal properties, the resulting
atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling
timescale according to existing models. Our findings suggest that substantial accretion during this
phase of planetary evolution may have been sufficient to impact the atmospheric composition and
thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Sérgio Sacani
The highest priority recommendation of the Astro2020 Decadal Survey for space-based astronomy
was the construction of an observatory capable of characterizing habitable worlds. In this paper series
we explore the detectability of and interference from exomoons and exorings serendipitously observed
with the proposed Habitable Worlds Observatory (HWO) as it seeks to characterize exoplanets, starting
in this manuscript with Earth-Moon analog mutual events. Unlike transits, which only occur in systems
viewed near edge-on, shadow (i.e., solar eclipse) and lunar eclipse mutual events occur in almost every
star-planet-moon system. The cadence of these events can vary widely from ∼yearly to multiple events
per day, as was the case in our younger Earth-Moon system. Leveraging previous space-based (EPOXI)
lightcurves of a Moon transit and performance predictions from the LUVOIR-B concept, we derive
the detectability of Moon analogs with HWO. We determine that Earth-Moon analogs are detectable
with observation of ∼2-20 mutual events for systems within 10 pc, and larger moons should remain
detectable out to 20 pc. We explore the extent to which exomoon mutual events can mimic planet
features and weather. We find that HWO wavelength coverage in the near-IR, specifically in the 1.4 µm
water band where large moons can outshine their host planet, will aid in differentiating exomoon signals
from exoplanet variability. Finally, we predict that exomoons formed through collision processes akin
to our Moon are more likely to be detected in younger systems, where shorter orbital periods and
favorable geometry enhance the probability and frequency of mutual events.
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...Sérgio Sacani
Mars is a particularly attractive candidate among known astronomical objects
to potentially host life. Results from space exploration missions have provided
insights into Martian geochemistry that indicate oxychlorine species, particularly perchlorate, are ubiquitous features of the Martian geochemical landscape. Perchlorate presents potential obstacles for known forms of life due to
its toxicity. However, it can also provide potential benefits, such as producing
brines by deliquescence, like those thought to exist on present-day Mars. Here
we show perchlorate brines support folding and catalysis of functional RNAs,
while inactivating representative protein enzymes. Additionally, we show
perchlorate and other oxychlorine species enable ribozyme functions,
including homeostasis-like regulatory behavior and ribozyme-catalyzed
chlorination of organic molecules. We suggest nucleic acids are uniquely wellsuited to hypersaline Martian environments. Furthermore, Martian near- or
subsurface oxychlorine brines, and brines found in potential lifeforms, could
provide a unique niche for biomolecular evolution.
Continuum emission from within the plunging region of black hole discsSérgio Sacani
The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a
powerful probe of the mass and spin of the central black hole. The vast majority of existing ‘continuum fitting’ models neglect
emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however,
find non-zero emission sourced from these regions. In this work, we extend existing techniques by including the emission
sourced from within the plunging region, utilizing new analytical models that reproduce the properties of numerical accretion
simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component,
but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component
has been added in by hand in an ad hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum
of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional
models that neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of
intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820 + 070 black hole spin
which must be low a• < 0.5 to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission
component in the MAXI J1820 + 070 spectrum between 6 and 10 keV, highlighting the necessity of including this region. Our
continuum fitting model is made publicly available.
WASP-69b’s Escaping Envelope Is Confined to a Tail Extending at Least 7 RpSérgio Sacani
Studying the escaping atmospheres of highly irradiated exoplanets is critical for understanding the physical
mechanisms that shape the demographics of close-in planets. A number of planetary outflows have been observed
as excess H/He absorption during/after transit. Such an outflow has been observed for WASP-69b by multiple
groups that disagree on the geometry and velocity structure of the outflow. Here, we report the detection of this
planet’s outflow using Keck/NIRSPEC for the first time. We observed the outflow 1.28 hr after egress until the
target set, demonstrating the outflow extends at least 5.8 × 105 km or 7.5 Rp This detection is significantly longer
than previous observations, which report an outflow extending ∼2.2 planet radii just 1 yr prior. The outflow is
blueshifted by −23 km s−1 in the planetary rest frame. We estimate a current mass-loss rate of 1 M⊕ Gyr−1
. Our
observations are most consistent with an outflow that is strongly sculpted by ram pressure from the stellar wind.
However, potential variability in the outflow could be due to time-varying interactions with the stellar wind or
differences in instrumental precision.
Deep Behavioral Phenotyping in Systems Neuroscience for Functional Atlasing a...Ana Luísa Pinho
Functional Magnetic Resonance Imaging (fMRI) provides means to characterize brain activations in response to behavior. However, cognitive neuroscience has been limited to group-level effects referring to the performance of specific tasks. To obtain the functional profile of elementary cognitive mechanisms, the combination of brain responses to many tasks is required. Yet, to date, both structural atlases and parcellation-based activations do not fully account for cognitive function and still present several limitations. Further, they do not adapt overall to individual characteristics. In this talk, I will give an account of deep-behavioral phenotyping strategies, namely data-driven methods in large task-fMRI datasets, to optimize functional brain-data collection and improve inference of effects-of-interest related to mental processes. Key to this approach is the employment of fast multi-functional paradigms rich on features that can be well parametrized and, consequently, facilitate the creation of psycho-physiological constructs to be modelled with imaging data. Particular emphasis will be given to music stimuli when studying high-order cognitive mechanisms, due to their ecological nature and quality to enable complex behavior compounded by discrete entities. I will also discuss how deep-behavioral phenotyping and individualized models applied to neuroimaging data can better account for the subject-specific organization of domain-general cognitive systems in the human brain. Finally, the accumulation of functional brain signatures brings the possibility to clarify relationships among tasks and create a univocal link between brain systems and mental functions through: (1) the development of ontologies proposing an organization of cognitive processes; and (2) brain-network taxonomies describing functional specialization. To this end, tools to improve commensurability in cognitive science are necessary, such as public repositories, ontology-based platforms and automated meta-analysis tools. I will thus discuss some brain-atlasing resources currently under development, and their applicability in cognitive as well as clinical neuroscience.
What is greenhouse gasses and how many gasses are there to affect the Earth.moosaasad1975
What are greenhouse gasses how they affect the earth and its environment what is the future of the environment and earth how the weather and the climate effects.
When I was asked to give a companion lecture in support of ‘The Philosophy of Science’ (https://shorturl.at/4pUXz) I decided not to walk through the detail of the many methodologies in order of use. Instead, I chose to employ a long standing, and ongoing, scientific development as an exemplar. And so, I chose the ever evolving story of Thermodynamics as a scientific investigation at its best.
Conducted over a period of >200 years, Thermodynamics R&D, and application, benefitted from the highest levels of professionalism, collaboration, and technical thoroughness. New layers of application, methodology, and practice were made possible by the progressive advance of technology. In turn, this has seen measurement and modelling accuracy continually improved at a micro and macro level.
Perhaps most importantly, Thermodynamics rapidly became a primary tool in the advance of applied science/engineering/technology, spanning micro-tech, to aerospace and cosmology. I can think of no better a story to illustrate the breadth of scientific methodologies and applications at their best.
Travis Hills' Endeavors in Minnesota: Fostering Environmental and Economic Pr...Travis Hills MN
Travis Hills of Minnesota developed a method to convert waste into high-value dry fertilizer, significantly enriching soil quality. By providing farmers with a valuable resource derived from waste, Travis Hills helps enhance farm profitability while promoting environmental stewardship. Travis Hills' sustainable practices lead to cost savings and increased revenue for farmers by improving resource efficiency and reducing waste.
BREEDING METHODS FOR DISEASE RESISTANCE.pptxRASHMI M G
Plant breeding for disease resistance is a strategy to reduce crop losses caused by disease. Plants have an innate immune system that allows them to recognize pathogens and provide resistance. However, breeding for long-lasting resistance often involves combining multiple resistance genes
Comparing Evolved Extractive Text Summary Scores of Bidirectional Encoder Rep...University of Maribor
Slides from:
11th International Conference on Electrical, Electronics and Computer Engineering (IcETRAN), Niš, 3-6 June 2024
Track: Artificial Intelligence
https://www.etran.rs/2024/en/home-english/
ESPP presentation to EU Waste Water Network, 4th June 2024 “EU policies driving nutrient removal and recycling
and the revised UWWTD (Urban Waste Water Treatment Directive)”
Phenomics assisted breeding in crop improvementIshaGoswami9
As the population is increasing and will reach about 9 billion upto 2050. Also due to climate change, it is difficult to meet the food requirement of such a large population. Facing the challenges presented by resource shortages, climate
change, and increasing global population, crop yield and quality need to be improved in a sustainable way over the coming decades. Genetic improvement by breeding is the best way to increase crop productivity. With the rapid progression of functional
genomics, an increasing number of crop genomes have been sequenced and dozens of genes influencing key agronomic traits have been identified. However, current genome sequence information has not been adequately exploited for understanding
the complex characteristics of multiple gene, owing to a lack of crop phenotypic data. Efficient, automatic, and accurate technologies and platforms that can capture phenotypic data that can
be linked to genomics information for crop improvement at all growth stages have become as important as genotyping. Thus,
high-throughput phenotyping has become the major bottleneck restricting crop breeding. Plant phenomics has been defined as the high-throughput, accurate acquisition and analysis of multi-dimensional phenotypes
during crop growing stages at the organism level, including the cell, tissue, organ, individual plant, plot, and field levels. With the rapid development of novel sensors, imaging technology,
and analysis methods, numerous infrastructure platforms have been developed for phenotyping.
This presentation explores a brief idea about the structural and functional attributes of nucleotides, the structure and function of genetic materials along with the impact of UV rays and pH upon them.
1. Spectroscopic Evidence for a Temperature Inversion in the
Dayside Atmosphere of the Hot Jupiter WASP-33b
Korey Haynes1,2,6
, Avi M. Mandell1
, Nikku Madhusudhan3
, Drake Deming4
, Heather
Knutson5
ABSTRACT
We present observations of two occultations of the extrasolar planet WASP-
33b using the Wide Field Camera 3 (WFC3) on the HST, which allow us to
constrain the temperature structure and composition of its dayside atmosphere.
WASP-33b is the most highly irradiated hot Jupiter discovered to date, and
the only exoplanet known to orbit a δ-Scuti star. We observed in spatial scan
mode to decrease instrument systematic effects in the data, and removed fluc-
tuations in the data due to stellar pulsations. The RMS for our final, binned
spectrum is 1.05 times the photon noise. We compare our final spectrum, along
with previously published photometric data, to atmospheric models of WASP-
33b spanning a wide range in temperature profiles and chemical compositions.
We find that the data require models with an oxygen-rich chemical composition
and a temperature profile that increases at high altitude. We also find that our
spectrum displays an excess in the measured flux towards short wavelengths that
is best explained as emission from TiO. If confirmed by additional measurements
at shorter wavelengths, this planet would become the first hot Jupiter with a
temperature inversion that can be definitively attributed to the presence of TiO
in its dayside atmosphere.
Subject headings: stars: planetary systems - eclipses - techniques: photometric -
techniques: 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 of Astronomy, University of Cambridge, Cambridge CB3 0HA, UK
4
Department of Astronomy, University of Maryland, College Park, MD 20742, USA
5
Division of Geological & Planetary Sciences, California Institute of Technology, Pasadena, CA 91125,
USA
6
Corresponding Email: khaynes0112@gmail.com
arXiv:1505.01490v1[astro-ph.EP]6May2015
2. – 2 –
1. Introduction
One of the most intriguing areas of study in the field of exoplanet characterization is
the temperature structure of exoplanet atmospheres. Hot Jupiters represent an extreme end
of the exoplanet distribution: they orbit very close to their host stars, which subjects them
to an intense amount of stellar radiation. Also due to their proximity, they likely become
tidally locked on astrophysically short timescales (Guillot et al. 1996), and are heated only
on the side facing the star. This results in strong zonal winds (Showman et al. 2008) that
redistribute the heat, with the dynamics of this redistribution dictated by the physical and
thermal structure of the planet’s atmosphere.
Temperature inversions were an early prediction from atmospheric models of highly
irradiated planets (Hubeny et al. 2003; Fortney et al. 2008), which demonstrated that strong
absorption of incident UV/visible irradiation by high-temperature absorbers such as TiO and
VO, which are commonly found in low-mass stars and brown dwarfs, could lead to thermal
inversions in their observable atmospheres. Evidence for the existence of thermal inversions
began with the first secondary eclipse measurements of HD209458b taken with the IRAC
camera on Spitzer by Knutson et al. (2008), who measured larger eclipse depths in spectral
regions with higher opacity due to features of H2O and CO (4.5 and 5.6 µm) compared with
nearby bands measuring the deeper thermal continuum (3.6 and 8 µm). However, more
recent analyses of HD209458b by Diamond-Lowe et al. (2014) and Schwarz et al. (2015)
do not support an inverted atmophere model; additionally, indications for the presence
or absence of an inversion in other planets based on Spitzer/IRAC data appear to defy
predictions based on the level of incident radiation or the overall equilibrium temperature of
the atmosphere (Machalek et al. 2008; Fressin et al. 2010, and others). More recent models
have suggested that heavy molecules such as TiO and VO may not remain suspended in
the upper atmosphere of Jupiter-mass planets (Spiegel et al. 2009), and searches for specific
spectral signatures of TiO in the optical have been unsuccessful (Sing et al. 2013; but see
also Hoeijmakers et al. 2014 for discussion of incompleteness in the TiO line list contributing
to inabilities to confirm observational detections). Recent theories have postulated several
additional atmospheric processes that could play a role in the formation of inversions, such as
the production of photochemical sulfur-based hazes (Zahnle et al. 2009) or the inhibition of
oxide formation due to a super-solar C/O ratio (Madhusudhan 2012). Furthermore, Knutson
et al. (2010) explored the possibility that the absorbing molecular species may be destroyed
by photodissociation and may, hence, be affected by the activity of the host star.
Progress on understanding the origin and conditions required for temperature inversions
has been further hampered by a lack of high-quality data for most sources. Only a single
unambiguous spectrally resolved measurement of a molecular feature in the eclipse spectrum
3. – 3 –
of a planet, the detection of water absorption in the WFC3 spectrum of WASP-43 b by Krei-
dberg et al. (2014), has been published to date. Eclipse measurements for most transiting
exoplanets comprise only the broadband Spitzer/IRAC filters, making the conclusions largely
model-dependent and subject to possible systematic offsets or uncertainties. The inference of
thermal inversions from IR photometry is based solely on our ability to determine whether
there is a larger-than-expected flux from molecular bands compared with the continuum.
Warm Spitzer photometry has now measured two-band eclipse depths for a large number of
planets, but while these measurements can provide some indication of a potential inversion,
such data cannot uniquely identify inverted atmospheres because of degeneracies between
atmospheric composition and structure (Madhusudhan & Seager 2010; Stevenson et al. 2010;
Moses et al. 2013). In particular, Madhusudhan & Seager (2010) showed that with only a
few data points, this interpretation is heavily dependent on the assumed composition of the
planet and the accuracy of the uncertainties ascribed to each measurement. A subsequent
Bayesian retrieval analysis on a subset of well-observed planets covering a wide range of
effective temperatures by Line & Yung (2013) showed that the data are inconsistent with
thermal inversions for many of the planets expected to have an inversion due to the afore-
mentioned theories for the physical origin of the phenomenon. More recently, a new analysis
by Diamond-Lowe et al. (2014) and Schwarz et al. (2015) revealed that a thermal inversion
is not necessary to explain the Spitzer observations of HD 209458b, previously considered
the prototypical example of a planet with an inverted atmosphere. Hansen et al. (2014) has
also suggested that the uncertainties on many older, single-visit Spitzer eclipse depths may
be significantly higher than previously reported, resulting in data sets that are essentially
consistent with featureless blackbody spectra.
It is therefore critical that we further investigate planets that provide the best chance
for confirming the presence of temperature inversions, in order to better constrain the actual
temperature structure of these planets and clarify the role of various stellar and planetary
characteristics in defining this structure. Here we present new secondary eclipse (or occul-
tation) observations of WASP-33b, one of the largest and hottest planets known, using the
Wide Field Camera 3 (WFC3) on HST. WASP-33 is an A-type δ-Scuti star and its planet,
WASP-33b, is one of the most highly irradiated planets discovered to date, orbiting once
every 1.22 days (Cameron et al. 2010; Herrero et al. 2011). WASP-33b is unique, being
the only exoplanet yet discovered to orbit a δ-Scuti star. Multiple observations of the host
star over wavelengths ranging from the visible to the infrared have shown oscillations with a
range of frequencies, and amplitudes on the order of 1 mmag. Given the extreme irradiation
received by WASP-33b, it is one of the most likely hot Jupiters to host a thermal inversion as
TiO/VO, if present, would be expected to be in the gaseous phase throughout the observable
dayside atmosphere, thereby causing a thermal inversion.
4. – 4 –
Previous occultation observations in the infrared (Deming et al. 2012) concluded that
WASP-33b might host a temperature inversion with a solar composition atmosphere, or a
non-inverted atmosphere with enhanced carbon abundance. The inversion scenario is advo-
cated by de Mooij et al. (2013), based on WASP-33b’s apparent inefficient heat redistribution,
which was also noted by Smith et al. (2011). Our spectroscopic observations with WFC3
cover a wavelength range from 1.1 to 1.7 µm, which provides a valuable opportunity to con-
firm the presence of an inversion in WASP-33b. The WFC3 spectral range covers strong
infrared molecular bands of H2O and TiO, both of which are expected to be abundant in
the atmosphere of WASP-33b, assuming a solar abundance composition. Assuming these
molecules contribute significant opacity at the height of the thermal inversion, the presence
of a thermal inversion would lead to emission features in the dayside spectrum due to both
these molecules in the WFC3 range, as opposed to absorption features if no thermal inversion
is present.
We describe the observations in Section 2, data reduction in Section 3, removal of stellar
oscillations and analysis strategies in Section 4, and discussion of results in Section 5.
2. Observations
Two occultations of WASP-33 were observed on November 25, 2012 and January 14,
2013. We used WFC3’s infrared G141 grism, which provides slitless spectra from 1.1 µm to
1.7 µm at a resolving power of 130 (Dressel 2012). Each target was allocated 5 HST orbits,
which was sufficient to cover a single planetary occultation while including periods of the
orbit both before and after occultation.
Both sets of observations were taken using the 256 x 256 sub-array with 7 non-destructive
reads per exposure, using the RAPID sampling sequence. The data were observed in spatial
scan mode (McCullough & MacKenty 2012), which increases the photon collection efficiency
of the detector, and additionally has been shown to decrease systematic patterns in the
data that can result from persistent levels of high flux on individual pixels. All scans were
performed in the same direction. See Table 1 for details.
3. Data Reduction
We used the series of single-exposure “ima” images produced by the WFC3 calwf3
pipeline for our data analysis. The “ima” files are fully reduced data products with the
exception of a step to combine multiple reads. The final stage “flt” files provided by the
5. – 5 –
Space Telescope Science Institute are not appropriate for use in spatial scan mode, since
the additional pipeline processing for combining multiple reads does not account for the
motion of the source on the detector in spatial scan mode. We followed the methodology of
Deming et al. (2013) to produce 2D spectral frames from the “ima” files provided on MAST.
We began by applying a top-hat mask in the spatial dimension of each read, the width of
which is 20 pixels tall in order to fully cover the stellar PSF. Areas outside the mask were
zeroed. We then subtracted subsequent reads, and then added the differenced frames to
create one scanned image. We used our own strategy from Mandell et al. (2013) to search
for and correct bad pixels within the combined spectral frames, and collapse the images
into 1D spectra. We used the modified coefficients from Wilkins et al. (2014) to produce
the wavelength and wavelength-dependent flat-field calibrations. For background correction,
we subtracted a single background value from each difference pair in the WASP-33 “ima”
files before applying the top-hat mask. The background subtraction decreases the overall
flux level of each light curve, thereby increasing the measured eclipse depth compared with
non-background subtracted frames. We determined the change in eclipse depth for the band-
integrated light curves to be 140 and 110 ppm for Visit 1 and Visit 2, respectively; these
values were constant across the spectrum.
We trimmed roughly 70 pixels from either end of the spectral extent, to remove the
parts of the spectrum with low sensitivity. After trimming the edges of the spectrum, the
spectrum covers the region between approximately 1.13 and 1.63 µm. We also identified the
strong Paschen β stellar feature at 1.28 µm, and took care to isolate it when defining our
spectral bins. In an oscillating star, such spectral features may have variable line profiles,
which could cause sharp changes in flux and add additional noise.
4. Analysis and Results
In the following sections, we describe in detail our fitting process. Briefly, we began with
the band-integrated curve, meaning we summed over all wavelengths to form one photomet-
ric light curve. We used this higher sensitivity light curve to fit for wavelength-invariant
parameters and determine the strongest signals due to stellar pulsations. We used the resid-
uals of this band-integrated curve as a model for otherwise uncorrected sources of correlated
noise, such as additional stellar oscillations or instrument systematics. We used binned light
curves comprising (on average) 10 columns/channels in order to investigate wavelength de-
pendent behavior, especially the change of eclipse depth with wavelength, and corrected for
spectral and spatial drift of the detector with time.
6. – 6 –
4.1. Identifying and Fitting Trends
4.1.1. Stellar Oscillations
WASP-33 is known to be an oscillating δ-Scuti star whose pulsation frequencies have
been measured over multiple campaigns (Herrero et al. 2011; Smith et al. 2011; Deming et al.
2012; Sada et al. 2012; de Mooij et al. 2013; Kov´acs et al. 2013; von Essen et al. 2013) across
a wide range of wavelengths, and many different pulsation frequencies have been determined
by these studies. However, since multiple oscillation modes are to be expected, and that
the strength of these modes will vary with wavelength, observations taken across a range
of spectral bands and at various times should not be expected to have perfect agreement,
nor can we expect exact comparisons across data sets. The incomplete temporal sampling
caused by HST orbits complicates characterization of the oscillation modes in our data, and
so we explored different avenues for constraining the detectable pulsation frequencies and
removing the stellar oscillations.
We used sine functions to model the stellar pulsations. While a non-parametric ap-
proach such as Gaussian Processes might allow more accurate modeling of stellar pulsations,
which can be quasi-periodic, previous observing campaigns using parametric aproaches did
not suffer from the incomplete temporal sampling in our data, and so by following their ex-
ample we were able to make comparisons between our best-fit frequencies and more complete
datasets.
We divided frequency space into regions based on the frequencies identified by previous
observing campaigns and allowed our MCMC models to fit, iteratively or simultaneously,
between 1 and 3 sine curves restricted to those regions of frequency space. We used Bayesian
information criterion (BIC; Schwarz 1978; Liddle 2004) to determine the best combination
of sine terms. While previous measurements have shown that the phase of stellar oscillations
can change slightly with wavelength (Conidis et al. 2010), the potential amplitude of these
changes would be very small across the WFC3 wavelength range, and we did not attempt
to fit for any phase change with wavelength. We find that two sine curves achieve the best
results without overfitting the data, and that the frequencies and amplitudes identified are
robust whether we fit the sine curves simultaneously or in sequence. The results are shown in
Table 2, and our best-fit frequencies agree approximately with previously determined values.
Red noise remains in the residuals after removal of the two sine curves representing
the stellar oscillation modes, indicating that we are unable to fully characterize either the
stellar oscillations or underlying instrument systematics. The instrument systematics are
weak in spatial scan mode, but still present (Deming et al. 2013). However, as we describe
in later sections, the remaining red noise in the band-integrated light curve will not affect
7. – 7 –
Table 1. Observations of WASP-33
Visit 1 Visit 2
Time of first scan (MJD UT) 56256.405 56306.455
Planetary orbital phase at first scan 0.328 0.354
Time of last scan (MJD UT) 56256.687 56306.746
Planetary orbital phase at last scan 0.549 0.583
Number of scans 119 119
Number of HST orbits 5 5
Detector subarray size 256 256
Detector reads per scan 7 7
Duration of scan (s) 51.7 51.7
Signal level on detector (electrons pixel −1
) 4.0-7.3 × 104
4.0-7.3 × 104
Table 2. Fitted frequencies and amplitudes of WASP-33’s stellar oscillations.
Frequency Amplitude Visit
19.88 ± 0.32 0.62 ± 0.05 Visit 1
29.65 ± 0.48 0.32 ± 0.04 Visit 1
14.40 ± 0.56 0.65 ± 0.16 Visit 2
22.16 ± 0.57 0.50 ± 0.07 Visit 2
8. – 8 –
our relative wavelength-dependent eclipse depths since we subtract a scaled version of the
residual noise from each bin. Additionally, because the first orbit of WFC3 observations
tends to be more noisy than subsequent orbits (Mandell et al. 2013; Deming et al. 2012),
we do not include this orbit for the band-integrated fitting process (including fitting for the
stellar oscillations), though we do incorporate it later in our wavelength-dependent relative
analysis.
4.1.2. Nonlinearity Correction
WASP-33 is an early-type star, and the flux incident on the detector at the short-
est wavelength of the grism response is almost a factor of two larger than the flux at the
longest wavelength. Since we want to optimize the photon-limited SNR at even the longest
wavelength, we exposed the spectra to the highest possible fluence levels, reaching 7 × 104
electrons per pixel at the short wavelength end. Since this is comparable to the full well
value of the detector, we applied a correction for detector nonlinearity, as described in Sec.
6.5.1 of the WFC3 Data Handbook 2.1. We used coefficients valid for quadrant one of the
detector, extracted from the calibration files at STScI. Our calculated correction increases
the eclipse depths by 25 parts per million at our shortest wavelength, decreasing to about 6
parts per million at the longest wavelength we analyze. These corrections do not affect our
scientific conclusions, which would be virtually identical if we had omitted the non-linearity
correction.
4.1.3. Spectral Shifts With Time
In order to correct for possible variations in channel flux due to shifts across the peak
of spectral features with time, we calculated the shift in the horizontal/spectral direction
referenced to a template exposure from our data. We examined two main strategies for
measuring the magnitude of the shift with time. Our initial method was to measure the
spectrum at the steeply sloped edges of the grism response. Due to the steep slope, sensitivity
due to spectral shifting is greatest at these wavelengths; however, these wavelengths mostly
do not overlap with those used in our final analysis, which are located across the central,
flatter region of the grism response. If the shift of spectrum is identical at all wavelengths,
this should not impact the final results; however, as we describe below, this was not the case.
The alternative strategy is to use only those wavelengths also used for the subsequent light
curve analysis. We describe our analysis of both strategies in greater detail, along with their
results, below.
9. – 9 –
In our initial analysis procedure, which was adapted from the method used in Mandell
et al. (2013), we fit the slope of the pixels at the short-wavelength and long-wavelength edges
of the spectrum. At these wavelengths the sensitivity curve causes the shape of the spectrum
to change most dramatically, resulting in a high-precision measurement of the spectral shift
in each exposure. The slopes measured at both edges of the spectrum were averaged to
further decrease the effective uncertainty of the measurement for each exposure. We used
the zeroth-order coefficient of this fit to determine the shift of each spectrum relative to the
first exposure in the time series.
We compared this strategy to that employed by Deming et al. (2013), which used instead
the central region of the spectrum to measure the shifts. This region is flat compared to the
edges, but does contain modulation in the spectral response. In this method, we created a
template spectrum comprised of an average of the exposures in the time series immediately
preceding and following eclipse. We interpolated the template spectrum onto a wavelength
grid shifted in either direction up to a pixel and a half, stepping in 0.001 pixel increments,
and saved each shifted spectrum. For each exposure, we compared the observed spectrum
with each shifted template spectrum. We also allowed the template spectrum a linear stretch
in intensity. We calculated the rms for each comparison; the shift corresponding to the lowest
rms is saved as our best-fit spectral shift.
We compared the two spectral shift measurement strategies, finding that if the edges of
the spectrum are included for the latter method, then the resulting shifts match the “edge
only” measurements of our method very closely. If instead only the central region of the
spectrum is used to determine the shifts, the measured shifts result in significant change in
the final eclipse spectrum. This result indicates that the shape or placement of the grism
sensitivity function changes as a function of time or placement on the detector, possibly
due to changes in the optical path as part of the thermal breathing modes of the telescope.
The horizontal shifts produced from the entire central region for the two visits are plotted
in Figure 1 for reference. The use of the “center-only” spectral shifts resulted in a lower
residual rms for the resulting light curves, indicating that the fit was improved by using
shifts derived from the same portion of the spectrum as the light curves themselves.
For consistency, we further extended this analysis by determining the specific spectral
shift for the specific portion of the spectrum associated with each binned light curve, and
using that set of shifts in the systematic decorrelation procedure. This has the advantage of
using the set of shifts that best describe the region of the spectrum used by each bin, since
the stellar intensity can vary greatly across the WFC3 grism response. However, the modest
wavelength range of the WFC3 grism and the minimal temperature variations expected due
to stellar oscillations ensure that our results show no spectral response to these pulsating
10. – 10 –
modes. As seen in Figure 2, the overall trend of the shifts with time does change with
wavelength, at least on a visit-long level; finer analysis is not possible due to the scatter
in the measurements. We found that using the bin-specific spectral shifts resulted in final
spectra for both visits that were consistent within uncertainties; on the contrary, using a
single shift value led to larger deviations between the visits, especially at short wavelengths.
Given this, we advocate careful inspection of the shift of the spectrum on the detector with
time, and for this work, we use these binned shifts for our final analysis.
In all cases, the shifts take the form of a repeating, inter-orbit pattern, as well as
a visit-long slope. We removed a visit-long linear trend from the xshifts, since a visit-
long trend in flux is also seen in previous WFC3 data sets and we choose to instead fit
for this slope as an independent parameter in our light curve fit. Alternatively, we also
examined the shift correction strategy from Deming et al. (2013), in which we interpolate
each exposure’s spectrum onto a shifted wavelength grid according to its best-measured shift
value (as determined by the rms) and use these shifted spectra for light curve fitting. In
this case, we do not use the scaled xshifts as a parameter in our MCMC fitting; instead, we
shift the spectra themselves. We find that the final derived spectrum is minimally affected
by the method of correction (interpolation vs xshift scaling), so long as the same wavelength
ranges (center, center + edges, or binned central region) are used to measure the shifts for
both methods.
Visit 2 Spectral Shift
−0.20 −0.10 0.00 0.10
Time From MidTransit (days)
Visit 1 Spectral Shift
−0.20 −0.10 0.00
Time From MidTransit (days)
−0.10
−0.05
0.00
0.05
0.10
X−Shift(Pixels)
Fig. 1.— Shifts in the spectral direction of the detector for both visits across the eclipse
duration. These shifts have been measured using the entire central region of the WFC3
wavelength coverage.
11. – 11 –
Visit 2 Spectral Shift
-0.10 0.00 0.10
Time From MidTransit (days)
Visit 1 Spectral Shift
-0.20 -0.10 0.00 0.10
Time From MidTransit (days)
-0.06
-0.04
-0.02
0.00
0.02
X-Shift(Pixels)
Unbinned Shifts
Bin 1 (1.16 µm)
Bin 2 (1.20 µm)
Bin 6 (1.37 µm)
-0.08
Bin 10 (1.56 µm)
Bin 11 (1.26 µm)
Fig. 2.— Shifts in the spectral direction of the detector, binned in time to show one data
point per HST orbit. The shifts measured from the entire central wavelength region (”un-
binned shifts”) are shown as black boxes. Refer to Figure 1 for the same data, unbinned in
time. A selection of ”binned shifts” are shown as colored circles. In this case, the spatial
shifts on the detector are measured for individual bins in wavelength, comprising about 10
channels/columns. While the bin from the most central region of the spectrum tracks closely
with the unbinned shifts, the bins from closer to the edges of the spectrum show trends that
differ both from the central region, and from visit to visit, suggesting that the shape or
placement of the grism sensitivity function is changing over the duration of a single visit.
12. – 12 –
4.2. Band-Integrated Eclipse Curve Fitting
We fit a band-integrated eclipse curve first, in order to determine best-fit values for those
parameters that are not wavelength dependent (as in the case for the stellar oscillations),
and in order to use the residuals of this band-integrated fit as a component in our analysis
of spectral channels or bins (see Mandell et al. (2013) for further explanation and details of
our fitting process). For both band-integrated and spectral channels/bins, we use a Markov
Chain Monte Carlo (MCMC) routine to determine our best-fit parameters. We locked all
orbital parameters, leaving open for fitting only the eclipse depth, slope, and sine terms.
Orbital parameters are listed in Table 3.
Our band-integrated time series is shown in various stages in Figure 3. While in practice
we fit all parameters simultaneously, we show here the effect of removing systematics one
at a time, and overplotting models for the slope, stellar oscillations, and finally the eclipse
model itself on iterative versions of the residuals. Due to the offset in the phase of the stellar
oscillations from one visit to the next, we fit each visit separately. We find agreement for
the two visits’ eclipse depths at the ≈ 1.5σ level, suggesting the impact of the remaining red
noise does not affect the determined eclipse depths significantly. We take for our final, best
fit eclipse depth the weighted mean of both visits; these values are listed in Table 4.
4.3. Fitting the Spectrally Binned Light Curves
For our wavelength-dependent analysis, we continued to fit each visit separately. How-
ever, for each visit we created a modified set of residuals from the band-integrated curve
fitting step by using one joint eclipse depth derived from the weighted mean of both visits,
rather than the individual best-fit eclipse depth from each visit. This provides a com-
mon band-integrated eclipse depth and standardizes the offset for each visit. Following the
methodology of Mandell et al. (2013), for each visit we incorporated into our model for the
eclipse of each spectral bin the residuals from the band-integrated light curve as well as a
systematic trend based on our measurements of the horizontal shift of the spectrum on the
detector over time. Both of these components were allowed a scaling factor which we left
open as an additional fitting parameter.
For the light curves of each channel or bin of channels we followed the band-integrated
methods for fitting using MCMC. We locked the same orbital parameters, and used a BIC
to determine whether the sine amplitudes, second order polynomial coefficient, residuals
scaling, and spectral shift scaling terms should be varied in our final analysis. The results
of open model parameters for individual bins are shown in Tables 5 and 6.
13. – 13 –
Table 3. Orbital and Stellar Parameters for WASP-33 a
Parameter Value
Period (days) 1.2198709
i (◦
) 86.2 ± 0.2
Rp/R∗
0.1143 ± 0.0002
a/R∗
3.69 ± 0.01
Semi-major axis (AU) 0.0259 +0.0002
−0.0005
e 0.00 ± 0.00
M∗ (M ) 1.561+0.045
−0.079
Spectral type A5
H band Magnitude 7.5
[Fe/H] 0.1 ± 0.2 c
a
Values from Kov´acs et al. (2013) except
where otherwise noted.
c
From Cameron et al. (2010).
Table 4. Band Integrated Results
Visit Eclipse Depth (%)
Visit 1 0.129 ± 0.009
Visit 2 0.110 ± 0.010
Combined 0.119 ± 0.006
14. – 14 –
WASP-33 Visit 1 White Light
0.996
0.997
0.998
0.999
1.000
1.001
1.002
1.003
NormalizedFlux
0.997
0.998
0.999
1.000
1.001
SlopeCorrected
0.997
0.998
0.999
1.000
1.001
SineCorrected
-0.20 -0.15 -0.10 -0.05 0.00 0.05 0.10
Time From Mid-Transit (days)
-0.0015
-0.0010
-0.0005
0.0000
0.0005
0.0010
0.0015
FinalTransitResiduals
WASP-33 Visit 2 White Light
0.997
0.998
0.999
1.000
1.001
1.002
1.003
NormalizedFlux
0.998
0.999
1.000
1.001
SlopeCorrected
0.997
0.998
0.999
1.000
1.001
SineCorrected
-0.15 -0.10 -0.05 0.00 0.05 0.10 0.15
Time From Mid-Transit (days)
-0.0015
-0.0010
-0.0005
0.0000
0.0005
0.0010
0.0015
FinalTransitResiduals
Fig. 3.— Band-integrated light curves for both visits in black with various model fits in red.
From top to bottom, the plots show a) the normalized data with a model for the visit-long
slope effect; b) the slope corrected data with a model for the stellar oscillations; c) the slope
and oscillation corrected data with a model for the eclipse; d) the residuals for the full fit.
Parameters are fit concurrently in MCMC, and are shown here in stages for clarification on
the relative contributions of each parameter.
15. – 15 –
Table 5. Visit 1: Open parameters for each bin as determined by BIC. For each binned
light curve, we test the significance of additional parameters with a BIC. Parameters
determined to significantly improve the fit are marked with a checkmark. We also tested a
residuals scaling coefficient, but found that it was not significant for any bin, and so we do
not include the null result in our table.
Wavelength Eclipse Out of Linear Sine XShifts 2nd Order
(µm) Depth Eclipse Flux Slope Amplitudes Scaling Coeffecient
1.16
1.20
1.24
1.28
1.32
1.37
1.41
1.46
1.51
1.56
1.61
Table 6. Visit 2: Open parameters for each bin as determined by BIC. For each binned
light curve, we test the significance of additional parameters with a BIC. Parameters
determined to significantly improve the fit are marked with a checkmark. We also tested a
residuals scaling coefficient and a second order polynomial term, but found that they were
not significant for any bins, and so we do not include the null results in our table.
Wavelength Eclipse Out of Linear Sine XShifts
(µm) Depth Eclipse Flux Slope Amplitudes Scaling
1.16
1.20
1.24
1.28
1.32
1.37
1.41
1.46
1.51
1.56
1.61
16. – 16 –
In general we find that the same terms make significant contributions for all the bins in
a single visit. The light curves are typically fit best by a model including a linear slope term,
unscaled band-integrated residuals and sine amplitudes, and a scaled version of the spectral
shifts. A fit for a second-order polynomial term for the visit-long trend (as suggested by
Stevenson et al. 2014) passed the BIC for most bins in Visit 1, but did not pass for any bins
in Visit 2. In all cases we chose the open parameters based on the BIC, on a bin-by-bin
basis.
0.0000
0.0005
0.0010
0.0015
0.0020
0.0025
EclipseDepth
1.1 1.2 1.3 1.4 1.5 1.6 1.7
Wavelength (μm)
0.0007
0.0008
0.0009
0.0010
0.0011
0.0012
0.0013
0.0014
EclipseDepth
Blackbody Curve
Visit 1
Visit 2
Combined
Fig. 4.— Top: Unbinned spectrum. Here, every detector column was assigned a wavelength,
a light curve was extracted, and the eclipse depth measured. Bottom: Binned spectrum. In
this case, multiple detector columns (ten columns, on average) were combined to make one
light curve, and the eclipse depth measured. Points are plotted at the mean wavelength for
each bin. For both plots, Visit 1 is in red, Visit 2 in blue, and the combined visits are in
black. Combined visits use a weighted mean. The largest discrepancies between visits are
seen near the stellar hydrogen line at 1.28 µm. Blackbody curve is shown as a dashed line,
with the best-fit planetary temperature of 2950 K.
Finally, we used an uncertainty-weighted mean to combine both visits in our final stage
17. – 17 –
of analysis, and these results are presented in Figure 4 and in Tables 7 (for the channels)
and 8 (for the bins). The results from both visits agree to within the 1-σ uncertainties for
almost all of the spectral bins, with the only major discrepancies appearing for two bins
near the stellar hydrogen line at 1.28 µm. This difference between visits for the hydrogen
feature is most likely due to variability in the depth of the stellar hydrogen line, which can
oscillate differently than the overall stellar continuum; we therefore consider this offset to be
uncorrectable without simultaneous measurements of other hydrogen spectral features.
19. – 19 –
4.4. Error Analysis
Our measured uncertainties were initially drawn from the MCMC posterior probability
distributions. In order to estimate the impact of our red noise, we used a modified version of
the residuals permutation method (Gillon et al. 2007), which involves shifting (permutating)
the time series of the residual noise via the “prayer-bead” method. In addition to shifting
the residual noise series left over from subtracting the light-curve model, we also inverted our
residuals (multiplying by -1) and reversed both the inverted and non-inverted residuals in
time to produce four different sets of residual noise. This yields 4 × N permutations, where
N is the number of exposures. We deemed this extra step useful because of the otherwise
limited number of possible permutations, which did not yield clear results from a traditional
residuals permutation analysis. For each channel or bin of channels, we use whichever is
higher, the uncertainty from MCMC or residuals permutation. For Visit 1, we find that
uncertainties from residuals permutation are on average 1.47 times higher than uncertainties
from MCMC, while for Visit 2 uncertainties from residuals permutation are 1.20 times higher.
We compared the photon noise to the rms of our white light, channel, and binned
data.We present our results in Table 9. In general we find that a substantial amount of
red noise remains in our band integrated light curves after removal of our best fit models.
However, the temporal morphology of the red noise does not change with wavelength, and
by subtracting our band-integrated residuals from each bin we are able to closely approach
the photon noise limit for our channels and bins. For our channels and bins, we find an rms
∼1.05 times the photon noise.
We also compare the measured MCMC + residuals permutation uncertainty to a pre-
dicted eclipse depth uncertainty. This prediction is based on the photon noise (or rms) and
the number of exposures in eclipse versus out of eclipse. The predicted uncertainty calcu-
lation assumes monotonic temporal spacing, which is not the case for WFC3 observations.
We find that our measured eclipse depth uncertainties for the channels and bins are between
∼1.5-2.5 times the predicted uncertainty, and we ascribe this to the contributions from the
uneven sampling of HST orbits and the residual red noise in the light curves. In previous
studies we found that the lack of complete and evenly spaced temporal coverage during the
eclipse is likely the cause of this failure to meet the predicted uncertainty, even for photon-
limited results. In this same comparison of measured versus predicted uncertainties, we note
that Visit 1 is further from the predicted uncertainty than Visit 2. Visit 1 has substantially
fewer points post-eclipse than Visit 2, which can be detrimental to the uncertainty on eclipse
fitting. Additionally, Visit 1 has a higher rate of spectral drift; while we perform corrections
for this drift, it remains an additional source of uncertainty. Given these factors, we feel
confident that the uncertainty we measure accurately reflects the sources of uncertainty in
20. – 20 –
the data.
5. Discussion
The hot Jupiter WASP-33b is one of the most irradiated hot Jupiters known and hence
is among the most favorable candidates to host a thermal inversion in its dayside atmosphere.
Studies in the past have suggested that extremely irradiated hot Jupiters should host ther-
mal inversions due to strong absorption of incident stellar light by absorbers such as TiO
and VO (Hubeny et al. 2003; Fortney et al. 2008). While Spiegel et al. (2009) have suggested
that TiO and VO may not remain aloft in some hot Jupiter atmospheres due to downward
drag by gravitational settling and condensation overtaking upward vertical mixing, the ex-
treme irradiation of WASP-33b should maintain atmospheric temperatures above the TiO
condensation point at all altitudes. However, alternate theories regarding the presence of
thermal inversions do not depend solely on temperature. Madhusudhan et al. (2011) and
Madhusudhan (2012) suggested that high C/O ratios could also deplete inversion-causing
compounds such as TiO and VO in hot Jupiters, thereby precluding the formation of thermal
inversions, and Knutson et al. (2010) proposed that the formation of inversions may instead
be correlated with chromospheric activity, implying that hot Jupiters orbiting active stars
are less likely to host thermal inversions (though their study did not include A-stars such as
WASP-33). While the existence of an inversion has been questioned in the archetype planet
HD 209458b (Diamond-Lowe et al. 2014; Schwarz et al. 2015), it is nevertheless reasonable
to hypothesize that strong stellar irradiation may cause substantial perturbations in the
temperature structure of hot Jupiter atmospheres. Given its extreme atmospheric condi-
tions and bright thermal emission, WASP-33b presents a valuable opportunity to constrain
the various hypotheses regarding thermal inversions in hot Jupiters, but previously reported
photometric observations from Spitzer and ground-based facilities have been unable to con-
clusively constrain the presence of an inversion (Deming et al. 2012; de Mooij et al. 2013).
With the inclusion of our spectrum from the WFC3 instrument on HST, we can significantly
improve these constraints.
5.1. Atmospheric Models and Parameter Retrieval
We modeled the temperature and composition of the planet’s atmosphere and retrieved
its properties using the retrieval technique of Madhusudhan et al. (2011) and Madhusudhan
(2012). The model computes line-by-line radiative transfer for a plane-parallel atmosphere
with the assumptions of hydrostatic equilibrium and global energy balance, as described in
21. – 21 –
1.2
1.0
0.8
0.6
1.2 1.3 1.4 1.5 1.6
WASP-33b
Inversion
No Inversion
Isothermal
Fplanet
/Fstar
(10-3
)
λ (μm)
1 105
8
6
4
2
2 3 4
WFC3 Data
No Inv. Inv.
Isoth.
Thermal
Profile
10-4
10-3
10-2
10-1
100
101
102
10-5
P(bar)
2.0 3.0 4.01.0
T (1000K)
Data (HST, Spitzer and Ground)
Fig. 5.— The left panel shows the observed and model thermal emission spectra of WASP-
33b. The observed WFC3 spectrum — weighted mean of the two visits — is shown in green
in the 1.1-1.7 µm range, also shown in the inset. All the other photometric observations
outside the WFC3 range from previous studies are also shown in green circles with error
bars. The solid curves show three best-fit model spectra corresponding to three model
scenarios: model with a thermal inversion (red), model without a thermal inversion (blue),
model with an isothermal atmosphere (grey). The gray dotted lines show two blackbody
spectra of the planet at temperatures of 1600 K and 3800 K. The corresponding colored
circles show the models binned at the same resolution as the data. The red model, which
corresponds to an oxygen-rich atmosphere with a thermal inversion, provides the best fit to
the data of all the models, as discussed in section 5. The right panel shows corresponding
model pressure-temperature profiles. The best-fit model with (without) a thermal inversion
is shown in red (blue), and the best-fit isothermal model is shown in grey.
22. – 22 –
Madhusudhan & Seager (2009). The composition and pressure-temperature (P-T) profile
of the dayside atmosphere are free parameters in the model. The model includes all the
major opacity sources expected in hot Jupiter atmospheres, namely H2O, CO, CH4, CO2,
C2H2, HCN, TiO, VO, and collision-induced absorption (CIA) due to H2-H2, as described
in Madhusudhan (2012). Our molecular line lists are obtained from Freedman et al. (2008),
Freedman (personal communication, 2009), Rothman (2005), Karkoschka & Tomasko (2010),
and Karkoschka (personal communication, 2011). Our CIA opacities are obtained from
Borysow et al. (1997) and Borysow (2002). A Kurucz model Castelli & Kurucz (2004) is
used for the stellar spectrum, and the stellar and planetary parameters are adopted from
Cameron et al. (2010).
We used our WFC3 observations together with previously published photometric data
(Deming et al. 2012; de Mooij et al. 2013; Smith et al. 2011) to obtain joint constraints on
the chemical composition and temperature structure of the planet. We explored the model
parameter space using a Markov Chain Monte Carlo algorithm (Madhusudhan et al. 2011)
and determined regions of model space that best explain the data. Our model space includes
models with and without thermal inversions, and models with oxygen-rich as well as carbon-
rich compositions. To accommodate the uncertainty in the overall band offset resulting from
our separate fits to the band-integrated light curve and each individual bin, we allowed a
constant offset on the WFC3 spectrum as a free parameter in our model fits, with a prior
constraint on the explored range based on the derived band-integrated uncertainty. Thus,
the model has twelve free parameters: five for the P-T profile, six for uniform mixing ratios of
six molecules (H2O, CO, CH4, CO2, C2H2, HCN), and one parameter for the WFC3 offset.
For the inversion models we set the TiO and VO abundances to their solar abundance
composition, whereas for the non-inversion model we assume TiO and VO are not present
in significant quantities. We ran separate model fits to the data assuming inverted and non-
inverted temperature profiles. We also investigated fits with isothermal temperature profiles
which result in featureless black body spectra; such a model has only two free parameters,
the isothermal temperature and the WFC3 offset.
We find that the sum-total of observations are best explained by a dayside atmosphere
with a temperature inversion and an oxygen-rich composition with a slightly sub-solar abun-
dance of H2O (see Figure 5). Previous photometric observations were consistent with two
distinct models (Deming et al. 2012): (a) a model with oxygen-rich composition with a
strong thermal inversion, and (b) a model with a carbon-rich composition but with no ther-
mal inversion. In our current work, we use our WFC3 observations to break the degeneracies
between these models, constrain the abundance of H2O, and provide strong evidence for a
temperature inversion caused by TiO. Figure 5 shows the observed spectrum along with
three best-fit model spectra in three model categories, one with a thermal inversion, one
23. – 23 –
without a thermal inversion, and another with an isothermal profile. The corresponding
pressure-temperature profiles are also shown. The best-fit inverted model has a χ2
of 98, the
best-fit non-inverted model has a χ2
of 243, and the best-fit blackbody (BB) spectrum has
a χ2
of 351. The causes of the remaining differences between the best-fit thermally-inverted
atmosphere model and the WFC3 data points are unclear at this point, but the relative
quality of fit between the three models can still be assessed robustly using the Bayesian
Information Criterion (BIC) given by BIC= χ2
+ k ln(N), where k is the number of free
parameters and N is the number of data points (15). The BIC for the three best-fit models
described above are 130.5 for the inverted model, 275.5 for the non-inverted model, and 356.4
for the blackbody model, implying that the inverted model provides a significantly better fit
to all the data and that the spectrum is not a blackbody.
We note that for each model category a population of ‘best-fit’ models are found with
similar χ2
values. Here we choose the most physically and chemically plausible model for
each category by determining the most likely combinations of molecular mixing ratios in
these solutions for the corresponding temperatures assuming equilibrium or non-equilibrium
chemistry (Madhusudhan 2012; Moses et al. 2013). For example, the criteria used for O-rich
models are that (a) CO must be comparable to the well-constrained H2O abundance, (b)
CH4,C2H2, and HCN are below 10−5
, and (c) CO2 is below 10−6
. The best-fit inversion
model has an O-rich composition with emission features due to CO, TiO, and H2O. The
mixing ratios of CO and H2O in the best-fit model are marginally sub-solar at ∼10−4
each,
whereas TiO and all the other molecules (e.g. CH4, C2H2, HCN) have nearly solar mixing
ratios; i.e. consistent with mixing ratios predicted by chemical equilibrium assuming solar
elemental abundances. The model fit to the 4.5 µm IRAC data point is due to the strong CO
emission feature, whereas the TiO emission feature is responsible for the fit in the z band
(at 0.9 µm) and the bluer half of our WFC3 data. Low-amplitude H2O emission features
provide reasonable fits to the remaining data in the WFC3 bandpass, whereas the continuum
emission is set by the temperature in the lower atmosphere of the inverted temperature profile
shown in Figure 5. On the contrary, the non-inversion model fit shown in Figure 5 has a
C-rich composition, as discussed below, consistent with the findings of Deming et al. (2013),
and has a significantly poorer fit compared to the O-rich inversion model as discussed above.
While the non-inversion model provides a very good fit to most of the WFC3 data, it provides
a significantly poor fit to the two bluest WFC3 data points, the z point, and the 4.5 µm
IRAC point.
Figure 6 shows the posterior probability distributions of the chemical compositions for
each model, inverted versus non-inverted. Note that even though the non-inverted model
provides much worse fits to the data than the inverted model, we show the posterior distri-
butions on compositions for both models for completeness. The posteriors for the inverted
24. – 24 –
model are consistent with an O-rich atmosphere, albeit of marginally sub-solar metallicity.
The H2O abundance is well constrained to between 10−5
- 10−4
, thanks to the WFC3 band-
pass which overlaps with a strong H2O band, whereas only upper-limits are obtained for all
the other molecules. The CO and H2O abundances are marginally sub-solar, but the upper-
limits on all the remaining molecules are consistent with a solar-type O-rich abundance
pattern. On the other hand, the posteriors for the non-inverted model similarly constrain
the H2O abundance but also require high abundances of HCN and C2H2 which are possible
only if the atmosphere is carbon-rich (i.e. C/O ≥ 1; Madhusudhan 2012; Kopparapu et al.
2013; Moses et al. 2013). However, these non-inverted models provide much worse fits to
the data compared to the inverted models, as discussed above, and hence the corresponding
constraints on the compositions are irrelevant. Nevertheless, these results still demonstrate
that it is in principle possible to detect C-rich atmospheres using a combination of WFC3
and Spitzer data.
The inversion model fit supports not just evidence for a temperature inversion, but also
argues that the temperature inversion is due to TiO. Figure 7 shows the observed spectrum
along with three model spectra, all including a thermal inversion: one is our best-fit model
including both TiO and water, one lacks TiO, and the third lacks both TiO and water. It
is clear that not only a temperature inversion, but also the presence of TiO (and water) is
required in order to achieve a truly good fit to the observed data. As shown in previous
studies (Hubeny et al. 2003; Fortney et al. 2008), strong absorption of incident light due
to the strong UV/visible opacity of TiO can cause thermal inversions in hot Jupiters. On
the other hand, the infrared opacity of TiO contributes to the emission features of TiO in
the emergent spectrum of the planet similar to the emission features of other molecules in
the planetary atmosphere caused by a thermal inversion. Thus the simultaneous inference
of a thermal inversion and the presence of TiO presents a self-consistent case in favor of the
results. Our inference of TiO supports previous theoretical predictions that TiO should be
abundant in the hottest of oxygen-rich hot Jupiters, due to the lack of an effective vertical
or day-night cold trap (Perez-Becker & Showman 2013; Parmentier et al. 2013). However,
previous searches for TiO in other hot Jupiters using transmission spectroscopy have yielded
either secure non-detections (Huitson et al. 2013; Sing et al. 2013) or inconclusive results
(D´esert et al. 2008). Two of these planets (HD 209458b and WASP-19b) are significantly
cooler than WASP-33b, but the lack of TiO absorption in the transmission spectrum of
WASP-12b (Teq ∼ 2500) may instead be due to either a high-altitude haze layer obscuring
any molecular absorption (Sing et al. 2013) or a chemical composition that is carbon-rich
rather than oxygen-rich (Madhusudhan et al. 2011; Stevenson et al. 2014).
However, since we cannot resolve individual spectral bands or lines of TiO in our spec-
trum, the evidence for TiO emission towards the blue end of WFC3 and in the z band is
25. – 25 –
0.04
0.03
0.02
0.01
0.00
0.020
0.005
0.010
0.015
0.000
0.025
0.020
0.015
0.010
0.005
0.000
0.020
0.005
0.010
0.015
0.000
0.025
0.020
0.015
0.010
0.005
0.000
0.025
0.020
0.015
0.010
0.005
0.000
Volume Mixing Ratio, Log(X/H2
)
-10 -9 -8 -7 -6 -10 -8 -6 -4
Volume Mixing Ratio, Log(X/H2
)
-10 -8 -6 -4
-10 -8 -6 -4
-10 -9 -8 -7 -6 -5 -4
H2
O CO
CH4
CO2
C2
H2
HCN
-10 -8 -6 -4
-5 -4
0.025
0.030
Inversion
No Inversion
Solar, 3000K
Fig. 6.— Posterior probability distributions of the molecular mixing ratios for models with a
thermal inversion (black) and without a thermal inversion (red), obtained by fitting the mod-
els to data using an MCMC retrieval method. Note that only the thermal inversion model
provides a good fit to the data (as discussed in section 5.1) and hence only the black pos-
terior distributions represent meaningful constraints on the atmospheric composition. The
non-inverted model does not provide good fits to the data but the corresponding posteriors
in the compositions are shown here for completeness. For reference, mixing ratios predicted
assuming solar elemental abundances and chemical equilibrium at 3000 K and 1 bar pressure
are marked with green dashed lines. For the inversion model, the derived H2O mixing ratio
is relatively well constrained to values of 10−5
- 10−4
whereas only upper-limits are obtained
for all the other molecules; H2O and CO are found to be moderately sub-solar, while the
other molecules are consistent with solar-abundance composition.
26. – 26 –
Fplanet
/Fstar
(10-3
)
λ (μm)
1 105
8
6
4
2
2 3 4
1.2
1.0
0.8
0.6
1.2 1.3 1.4 1.5 1.6
WASP-33b
Best-fit Inversion Model with TiO
Model without TiO and H2
O
WFC3 Data
Model without TiO
Data (HST, Spitzer and Ground)
Fig. 7.— Observed and model thermal emission spectra of WASP-33b, showing the effect
of the inclusion of water and TiO on model spectra that include a temperature inversion.
The observed WFC3 spectrum (green) and best-fit model (red) are as described in Figure
5, where the red line indicates an inverted model including TiO and water. The remaining
model curves show the effect of removing molecules from the model spectra: an inverted
model without contributions from TiO (blue), and an inverted model without TiO or water
(gray). It is clear that the presence of TiO is required to achieve a good fit.
27. – 27 –
not conclusive. Ostensibly, the presence of hazes/clouds in the atmosphere could lead to sig-
nificant particulate scattering at short wavelengths, as the scattering cross-sections typically
scale as an inverse-power-law of the wavelength (e.g. Evans et al. 2013; Sing et al. 2013).
However, such an interpretation is met with several challenges. Firstly, the blue-ward flux
would need to start rising abruptly below ∼1.25 µm, following a 20% increase in reflected
light over a 0.05µm spectral bin, which is inconsistent with the typical power law slope ex-
pected for the scattered light spectrum. Secondly, the planet orbits an A star (T ∼ 7400
K) for which the spectrum peaks at relatively short wavelengths (0.43 µm). Consequently,
the dominant contribution of the reflected light would be expected to be in the far blue
with significantly less contribution in the near-infrared which is where the current data need
strong flux. Therefore the contribution from emission by TiO represents the most plausible
explanation for the rise in the data at short wavelengths, but this inference can be further
verified by future observations using existing facilities. TiO has strong spectral features in
the red optical and near-infrared, between ∼0.7-1.1 µm as shown in Figure 7 (also see e.g.
Fortney et al. 2008; Madhusudhan 2012). Several existing instruments can enable observa-
tions in this bandpass, including HST WFC3 G102 grism spectroscopy in the ∼ 0.8-1.15 µm
range (Sing et al. 2014), and ground-based spectroscopy and/or photometry in the ∼0.7-1.2
µm range (e.g. Bean et al. 2011; F¨ohring et al. 2013; Chen et al. 2014).
Finally, we note that previous studies, both theoretical and observational, have sug-
gested that the hottest exoplanets may be the most inefficient at redistributing heat to their
night sides (Cowan & Agol 2011; Perez-Becker & Showman 2013). Our results are consistent
with those findings; if we compare the incoming radiation from the star with the outgo-
ing day-side flux from our best-fit inverted model, we derive a low day-night redistribution
( 15%), as would be expected for a planet with day-side temperatures above 2200K. In
contrast, the best-fit non-inverted model, which provides a poorer fit to the data compared
to the inverted model, has very efficient redistribution ( 50%).
6. Conclusion
In this paper we present our analysis of WFC3 observations of two occultations of
WASP-33b, a hot Jupiter orbiting a δ-Scuti star. We reduce and analyze the spectroscopic
time series for both visits, and correct for stellar oscillations of the star, as well as for motion
of the target on the detector. We bin our spectrum, and achieve an RMS ∼1.05 times the
photon noise. We compare our final emission spectrum to atmospheric models testing a range
of carbon to oxygen ratios and temperature profiles, and find strong evidence for an oxygen-
rich atmosphere that hosts a temperature inversion. We also present the first observational
28. – 28 –
evidence for TiO in the dayside of an exoplanet atmosphere. This is consistent with, and
improves upon, previous observations that could not discern between competing models, and
demonstrates the power of combining HST, Spitzer and ground-based observations to break
degeneracies in the composition and temperature structure of extrasolar planets. Future
measurements for a larger sample of exoplanets will help to determine the conditions under
which thermal inversions exist, and pave the way for more detailed investigations with future
instruments such as the James Webb Space Telescope.
7. Acknowledgements
The authors would like to thank the anonymous referee for thoughtful comments that
improved the paper. This work is based on observations made with the NASA/ESA Hub-
ble Space Telescope that were obtained at the Space Telescope Science Institute, which is
operated by the Association of Universities for Research in Astronomy, Inc., under NASA
contract NAS 5-26555. These observations are associated with program GO-12495. Support
for this work was provided by NASA through a grant from the Space Telescope Science
Institute, with additional support for data analysis provided by a grant from the NASA
Astrophysics Data Analysis Program (for K.H. and A.M.M.).
30. – 30 –
Table 9. Error Analysis. We compare photon noise, rms statistics, and both predicted
and measured uncertainties for each source. We show each of these statistics for the
band-integrated time series, binned data, and spectral channels. For the binned data and
spectral channels, the mean uncertainty is shown for each row. The predicted uncertainty
calculation assumes monotonic temporal spacing, which is not the case for WFC3
observations, and is therefore likely to underpredict the true uncertainty. The measured
uncertainty is drawn from the MCMC posterior distributions. The difference between the
predicted uncertainty and the uncertainty from MCMC therefore mostly reflects the
incomplete coverage over the light curve, while the difference between the rms and the
photon noise reflects the impact of additional noise beyond the photon noise.
Parameters Visit 1 Visit 2
Data points during eclipse 38 47
Data points out of eclipse 81 72
Channels
Photon noise (ppm) 419. 420.
RMS of residuals (ppm) 440. 437.
Predicted1 σed (ppm) 79.0 78.0
σed from MCMC+RP Data (ppm) 203. 121.
RMS/photon noise 1.05 1.04
MCMC Data/Pred. 2.57 1.55
0.042-Micron Bins (11 Total)
Photon noise (ppm) 181. 162.
RMS of residuals (ppm) 191. 187.
Predicted1 σed (ppm) 34.0 30.1
σed from MCMC+RP Data (ppm) 76.2 52.6
RMS/photon noise 1.07 1.17
MCMC Data/Pred. 2.33 1.79
Band Integrated Time Series
Photon noise (ppm) 47.3 46.6
RMS of residuals (ppm) 272. 331.
Predicted1 σed (ppm) 9.50 9.58
σed from MCMC+RP Data (ppm) 112. 90.5
RMS/photon noise 5.75 7.10
MCMC Data/Pred. 11.8 9.45
1Calculated from the photon noise and the number of
points during eclipse
31. – 31 –
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