Planets in highly eccentric orbits form a class of objects not seen within our Solar System. The most extreme case known amongst these objects is the planet orbiting HD 20782, with an orbital period of 597 days and an eccentricity of 0.96. Here we present new data and analysis for this system as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS). We obtained CHIRON spectra to perform an independent estimation of the fundamental stellar parameters. New radial velocities from AAT and PARAS observations during periastron passage greatly improve our knowledge of the eccentric nature of the orbit. The combined analysis of our Keplerian orbital and Hipparcos astrometry show that the inclination of the planetary orbit is > 1.22◦, ruling out stellar masses for the companion. Our long-term robotic photometry show that the star is extremely stable over long timescales. Photometric monitoring of the star during predicted transit and periastron times using MOST rule out a transit of the planet and reveal evidence of phase variations during periastron. These possible photometric phase variations may be caused by reflected light from the planet’s atmosphere and the dramatic change in star–planet separation surrounding the periastron passage.
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.
We discovered two transient events in the Kepler eld with light curves that strongly suggest they
are type II-P supernovae. Using the fast cadence of the Kepler observations we precisely estimate
the rise time to maximum for KSN2011a and KSN2011d as 10.50:4 and 13.30:4 rest-frame days
respectively. Based on ts to idealized analytic models, we nd the progenitor radius of KSN2011a
(28020 R) to be signicantly smaller than that for KSN2011d (49020 R) but both have similar
explosion energies of 2.00:3 1051 erg.
The rising light curve of KSN2011d is an excellent match to that predicted by simple models of
exploding red supergiants (RSG). However, the early rise of KSN2011a is faster than the models
predict possibly due to the supernova shockwave moving into pre-existing wind or mass-loss from the
RSG. A mass loss rate of 10 4 M yr 1 from the RSG can explain the fast rise without impacting
the optical
ux at maximum light or the shape of the post-maximum light curve.
No shock breakout emission is seen in KSN2011a, but this is likely due to the circumstellar inter-
action suspected in the fast rising light curve. The early light curve of KSN2011d does show excess
emission consistent with model predictions of a shock breakout. This is the rst optical detection of
a shock breakout from a type II-P supernova.
Periodic mass extinctions_and_the_planet_x_model_reconsideredSérgio Sacani
The 27 Myr periodicity in the fossil extinction record has been con-
firmed in modern data bases dating back 500 Myr, which is twice the time
interval of the original analysis from thirty years ago. The surprising regularity
of this period has been used to reject the Nemesis model. A second
model based on the sun’s vertical galactic oscillations has been challenged
on the basis of an inconsistency in period and phasing. The third astronomical
model originally proposed to explain the periodicity is the Planet
X model in which the period is associated with the perihelion precession
of the inclined orbit of a trans-Neptunian planet. Recently, and unrelated
to mass extinctions, a trans-Neptunian super-Earth planet has been proposed
to explain the observation that the inner Oort cloud objects Sedna
and 2012VP113 have perihelia that lie near the ecliptic plane. In this
Letter we reconsider the Planet X model in light of the confluence of the
modern palaeontological and outer solar system dynamical evidence.
Key Words: astrobiology - planets and satellites - Kuiper belt:
general - comets: general
Young remmants of_type_ia_supernovae_and_their_progenitors_a_study_of_snr_g19_03Sérgio Sacani
Type Ia supernovae, with their remarkably homogeneous light curves and spectra, have been used as
standardizable candles to measure the accelerating expansion of the Universe. Yet, their progenitors
remain elusive. Common explanations invoke a degenerate star (white dwarf) which explodes upon
reaching close to the Chandrasekhar limit, by either steadily accreting mass from a companion star
or violently merging with another degenerate star. We show that circumstellar interaction in young
Galactic supernova remnants can be used to distinguish between these single and double degenerate
progenitor scenarios. Here we propose a new diagnostic, the Surface Brightness Index, which can
be computed from theory and compared with Chandra and VLA observations. We use this method
to demonstrate that a double degenerate progenitor can explain the decades-long
ux rise and size
increase of the youngest known Galactic SNR G1.9+0.3. We disfavor a single degenerate scenario.
We attribute the observed properties to the interaction between a steep ejecta prole and a constant
density environment. We suggest using the upgraded VLA to detect circumstellar interaction in
the remnants of historical Type Ia supernovae in the Local Group of galaxies. This may settle the
long-standing debate over their progenitors.
Subject headings: ISM: supernova remnants | radio continuum: general | X-rays: general | bi-
naries: general | circumstellar matter | supernovae: general | ISM: individual
objects(SNR G1.9+0.3)
We present long-baseline Atacama Large Millimeter/submillimeter Array (ALMA) observations of
the 870 m continuum emission from the nearest gas-rich protoplanetary disk, around TW Hya, that
trace millimeter-sized particles down to spatial scales as small as 1 AU (20 mas). These data reveal
a series of concentric ring-shaped substructures in the form of bright zones and narrow dark annuli
(1{6AU) with modest contrasts (5{30%). We associate these features with concentrations of solids
that have had their inward radial drift slowed or stopped, presumably at local gas pressure maxima.
No signicant non-axisymmetric structures are detected. Some of the observed features occur near
temperatures that may be associated with the condensation fronts of major volatile species, but the
relatively small brightness contrasts may also be a consequence of magnetized disk evolution (the
so-called zonal
ows). Other features, particularly a narrow dark annulus located only 1 AU from the
star, could indicate interactions between the disk and young planets. These data signal that ordered
substructures on AU scales can be common, fundamental factors in disk evolution, and that high
resolution microwave imaging can help characterize them during the epoch of planet formation.
Keywords: protoplanetary disks | planet-disk interactions | stars: individual (TW Hydrae)
The characterization of_the_gamma_ray_signal_from_the_central_milk_way_a_comp...Sérgio Sacani
Past studies have identified a spatially extended excess of ∼1-3 GeV gamma rays from the region
surrounding the Galactic Center, consistent with the emission expected from annihilating dark
matter. We revisit and scrutinize this signal with the intention of further constraining its characteristics
and origin. By applying cuts to the Fermi event parameter CTBCORE, we suppress the tails
of the point spread function and generate high resolution gamma-ray maps, enabling us to more
easily separate the various gamma-ray components. Within these maps, we find the GeV excess
to be robust and highly statistically significant, with a spectrum, angular distribution, and overall
normalization that is in good agreement with that predicted by simple annihilating dark matter
models. For example, the signal is very well fit by a 36-51 GeV dark matter particle annihilating to
b
¯b with an annihilation cross section of σv = (1−3)×10−26 cm3
/s (normalized to a local dark matter
density of 0.4 GeV/cm3
). Furthermore, we confirm that the angular distribution of the excess is
approximately spherically symmetric and centered around the dynamical center of the Milky Way
(within ∼0.05◦
of Sgr A∗
), showing no sign of elongation along the Galactic Plane. The signal is
observed to extend to at least ' 10◦
from the Galactic Center, disfavoring the possibility that this
emission originates from millisecond pulsars.
Inverse Compton cooling limits the brightness temperature of the radiating plasma to a maximum of
1011.5 K. Relativistic boosting can increase its observed value, but apparent brightness temperatures
much in excess of 1013 K are inaccessible using ground-based very long baseline interferometry (VLBI)
at any wavelength. We present observations of the quasar 3C 273, made with the space VLBI mission
RadioAstron on baselines up to 171,000 km, which directly reveal the presence of angular structure as
small as 26 µas (2.7 light months) and brightness temperature in excess of 1013 K. These measurements
challenge our understanding of the non-thermal continuum emission in the vicinity of supermassive
black holes and require a much higher Doppler factor than what is determined from jet apparent
kinematics.
Keywords: galaxies: active — galaxies: jets — radio continuum: galaxies — techniques: interferometric
— quasars: individual (3C 273)
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,
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.
We discovered two transient events in the Kepler eld with light curves that strongly suggest they
are type II-P supernovae. Using the fast cadence of the Kepler observations we precisely estimate
the rise time to maximum for KSN2011a and KSN2011d as 10.50:4 and 13.30:4 rest-frame days
respectively. Based on ts to idealized analytic models, we nd the progenitor radius of KSN2011a
(28020 R) to be signicantly smaller than that for KSN2011d (49020 R) but both have similar
explosion energies of 2.00:3 1051 erg.
The rising light curve of KSN2011d is an excellent match to that predicted by simple models of
exploding red supergiants (RSG). However, the early rise of KSN2011a is faster than the models
predict possibly due to the supernova shockwave moving into pre-existing wind or mass-loss from the
RSG. A mass loss rate of 10 4 M yr 1 from the RSG can explain the fast rise without impacting
the optical
ux at maximum light or the shape of the post-maximum light curve.
No shock breakout emission is seen in KSN2011a, but this is likely due to the circumstellar inter-
action suspected in the fast rising light curve. The early light curve of KSN2011d does show excess
emission consistent with model predictions of a shock breakout. This is the rst optical detection of
a shock breakout from a type II-P supernova.
Periodic mass extinctions_and_the_planet_x_model_reconsideredSérgio Sacani
The 27 Myr periodicity in the fossil extinction record has been con-
firmed in modern data bases dating back 500 Myr, which is twice the time
interval of the original analysis from thirty years ago. The surprising regularity
of this period has been used to reject the Nemesis model. A second
model based on the sun’s vertical galactic oscillations has been challenged
on the basis of an inconsistency in period and phasing. The third astronomical
model originally proposed to explain the periodicity is the Planet
X model in which the period is associated with the perihelion precession
of the inclined orbit of a trans-Neptunian planet. Recently, and unrelated
to mass extinctions, a trans-Neptunian super-Earth planet has been proposed
to explain the observation that the inner Oort cloud objects Sedna
and 2012VP113 have perihelia that lie near the ecliptic plane. In this
Letter we reconsider the Planet X model in light of the confluence of the
modern palaeontological and outer solar system dynamical evidence.
Key Words: astrobiology - planets and satellites - Kuiper belt:
general - comets: general
Young remmants of_type_ia_supernovae_and_their_progenitors_a_study_of_snr_g19_03Sérgio Sacani
Type Ia supernovae, with their remarkably homogeneous light curves and spectra, have been used as
standardizable candles to measure the accelerating expansion of the Universe. Yet, their progenitors
remain elusive. Common explanations invoke a degenerate star (white dwarf) which explodes upon
reaching close to the Chandrasekhar limit, by either steadily accreting mass from a companion star
or violently merging with another degenerate star. We show that circumstellar interaction in young
Galactic supernova remnants can be used to distinguish between these single and double degenerate
progenitor scenarios. Here we propose a new diagnostic, the Surface Brightness Index, which can
be computed from theory and compared with Chandra and VLA observations. We use this method
to demonstrate that a double degenerate progenitor can explain the decades-long
ux rise and size
increase of the youngest known Galactic SNR G1.9+0.3. We disfavor a single degenerate scenario.
We attribute the observed properties to the interaction between a steep ejecta prole and a constant
density environment. We suggest using the upgraded VLA to detect circumstellar interaction in
the remnants of historical Type Ia supernovae in the Local Group of galaxies. This may settle the
long-standing debate over their progenitors.
Subject headings: ISM: supernova remnants | radio continuum: general | X-rays: general | bi-
naries: general | circumstellar matter | supernovae: general | ISM: individual
objects(SNR G1.9+0.3)
We present long-baseline Atacama Large Millimeter/submillimeter Array (ALMA) observations of
the 870 m continuum emission from the nearest gas-rich protoplanetary disk, around TW Hya, that
trace millimeter-sized particles down to spatial scales as small as 1 AU (20 mas). These data reveal
a series of concentric ring-shaped substructures in the form of bright zones and narrow dark annuli
(1{6AU) with modest contrasts (5{30%). We associate these features with concentrations of solids
that have had their inward radial drift slowed or stopped, presumably at local gas pressure maxima.
No signicant non-axisymmetric structures are detected. Some of the observed features occur near
temperatures that may be associated with the condensation fronts of major volatile species, but the
relatively small brightness contrasts may also be a consequence of magnetized disk evolution (the
so-called zonal
ows). Other features, particularly a narrow dark annulus located only 1 AU from the
star, could indicate interactions between the disk and young planets. These data signal that ordered
substructures on AU scales can be common, fundamental factors in disk evolution, and that high
resolution microwave imaging can help characterize them during the epoch of planet formation.
Keywords: protoplanetary disks | planet-disk interactions | stars: individual (TW Hydrae)
The characterization of_the_gamma_ray_signal_from_the_central_milk_way_a_comp...Sérgio Sacani
Past studies have identified a spatially extended excess of ∼1-3 GeV gamma rays from the region
surrounding the Galactic Center, consistent with the emission expected from annihilating dark
matter. We revisit and scrutinize this signal with the intention of further constraining its characteristics
and origin. By applying cuts to the Fermi event parameter CTBCORE, we suppress the tails
of the point spread function and generate high resolution gamma-ray maps, enabling us to more
easily separate the various gamma-ray components. Within these maps, we find the GeV excess
to be robust and highly statistically significant, with a spectrum, angular distribution, and overall
normalization that is in good agreement with that predicted by simple annihilating dark matter
models. For example, the signal is very well fit by a 36-51 GeV dark matter particle annihilating to
b
¯b with an annihilation cross section of σv = (1−3)×10−26 cm3
/s (normalized to a local dark matter
density of 0.4 GeV/cm3
). Furthermore, we confirm that the angular distribution of the excess is
approximately spherically symmetric and centered around the dynamical center of the Milky Way
(within ∼0.05◦
of Sgr A∗
), showing no sign of elongation along the Galactic Plane. The signal is
observed to extend to at least ' 10◦
from the Galactic Center, disfavoring the possibility that this
emission originates from millisecond pulsars.
Inverse Compton cooling limits the brightness temperature of the radiating plasma to a maximum of
1011.5 K. Relativistic boosting can increase its observed value, but apparent brightness temperatures
much in excess of 1013 K are inaccessible using ground-based very long baseline interferometry (VLBI)
at any wavelength. We present observations of the quasar 3C 273, made with the space VLBI mission
RadioAstron on baselines up to 171,000 km, which directly reveal the presence of angular structure as
small as 26 µas (2.7 light months) and brightness temperature in excess of 1013 K. These measurements
challenge our understanding of the non-thermal continuum emission in the vicinity of supermassive
black holes and require a much higher Doppler factor than what is determined from jet apparent
kinematics.
Keywords: galaxies: active — galaxies: jets — radio continuum: galaxies — techniques: interferometric
— quasars: individual (3C 273)
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,
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.
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
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
WHERE IS THE FLUX GOING? THE LONG-TERM PHOTOMETRIC VARIABILITY OF BOYAJIAN’S ...Sérgio Sacani
We present ∼ 800 days of photometric monitoring of Boyajian’s Star (KIC 8462852) from the AllSky
Automated Survey for Supernovae (ASAS-SN) and ∼ 4000 days of monitoring from the All Sky
Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian’s Star
has steadily decreased at a rate of 6.3 ± 1.4 mmag yr−1
, such that the star is now 1.5% fainter than it
was in February 2015. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian’s
Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a
monotonic decline. We analyze a sample of ∼ 1000 comparison stars of similar brightness located in
the same ASAS-SN field and demonstrate that the recent fading is significant at & 99.4% confidence.
The 2015 − 2017 dimming rate is consistent with that measured with Kepler data for the time period
from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models
for the star’s behavior proposed to date
Evidence for a_distant_giant_planet_in_the_solar_systemSérgio Sacani
A descoberta de um novo planeta, atualmente não é uma manchete que chama tanto assim a atenção das pessoas. Muito disso, graças ao Telescópio Espacial Kepler, que já descobriu quase 2000 exoplanetas e todo instante uma nova descoberta é anunciada, certo? Mais ou menos, a descoberta anunciada hoje, dia 20 de Janeiro de 2016, é um pouco diferente, pois não se trata de um exoplaneta, e sim de um novo planeta no Sistema Solar, e esse é um fato que intriga os astrônomos a muitos e muitos anos.
Porém, temos que ir com calma com esses anúncios. No artigo aceito para publicação no The Astronomical Journal (artigo no final do post), os autores, Mike Brown e Konstantin Batygin, do Instituto de Tecnologia da Califórnia, apresentaram o que eles dizem ser evidências circunstâncias fortes para a existência de um grande planeta ainda não descoberto, talvez, com uma massa 10 vezes a massa da Terra, orbitando os confins do nosso Sistema Solar, muito além da órbita de Plutão. Os cientistas inferiram sua presença, por meio de anomalias encontradas nas órbitas de seis objetos do chamado Cinturão de Kuiper.
O objeto, que os pesquisadores estão chamando de Planeta Nove, não chega muito perto do Sol, no ponto mais próximo da sua órbita ele fica a 30.5 bilhões de quilômetros, ou seja, cinco vezes a distância entre o Sol e Plutão. Apesar do seu grande tamanho, ele é muito apagado, e por isso ninguém até o momento conseguiu observá-lo.
Não existe ainda uma confirmação observacional da descoberta, mas as evidências são tão fortes que fizeram com que outros especialistas como Chad Trujilo do Observatório Gemini no Havaí e David Nesvorny, do Southwest Research Institute em Boulder no Colorado, ficassem impressionados e bem convencidos de que deve mesmo haver um grande planeta nas fronteiras da nossa vizinhança cósmica.
The canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
We report the discovery of an optical Einstein Ring in the Sculptor constellation,
IAC J010127-334319, in the vicinity of the Sculptor Dwarf Spheroidal Galaxy. It is
an almost complete ring ( 300◦) with a diameter of 4.5 arcsec. The discovery was
made serendipitously from inspecting Dark Energy Camera (DECam) archive imaging
data. Confirmation of the object nature has been obtained by deriving spectroscopic
redshifts for both components, lens and source, from observations at the 10.4 m Gran
Telescopio CANARIAS (GTC) with the spectrograph OSIRIS. The lens, a massive
early-type galaxy, has a redshift of z = 0.581 while the source is a starburst galaxy
with redshift of z = 1.165. The total enclosed mass that produces the lensing effect
has been estimated to be Mtot = (1.86 ± 0.23) · 1012M⊙.
We report the discovery of a new Kepler transiting circumbinary planet (CBP).
This latest addition to the still-small family of CBPs defies the current trend of known
short-period planets orbiting near the stability limit of binary stars. Unlike the previous
discoveries, the planet revolving around the eclipsing binary system Kepler-1647 has
a very long orbital period ( 1100 days) and was at conjunction only twice during
the Kepler mission lifetime. Due to the singular configuration of the system, Kepler-
1647b is not only the longest-period transiting CBP at the time of writing, but also one
of the longest-period transiting planets. With a radius of 1:060:01 RJup it is also the
largest CBP to date. The planet produced three transits in the light-curve of Kepler-
1647 (one of them during an eclipse, creating a syzygy) and measurably perturbed the
times of the stellar eclipses, allowing us to measure its mass to be 1:520:65 MJup.
The planet revolves around an 11-day period eclipsing binary consisting of two Solarmass
stars on a slightly inclined, mildly eccentric (ebin = 0:16), spin-synchronized
orbit. Despite having an orbital period three times longer than Earth’s, Kepler-1647b is
in the conservative habitable zone of the binary star throughout its orbit.
Detection of solar_like_oscillations_in_relies_of_the_milk_way_asteroseismolo...Sérgio Sacani
Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens
of thousands of field stars. Tests against independent estimates of these properties are however
scarce, especially in the metal-poor regime. Here, we report the detection of solar-like
oscillations in 8 stars belonging to the red-giant branch and red-horizontal branch of the globular
cluster M4. The detections were made in photometric observations from the K2 Mission
during its Campaign 2. Making use of independent constraints on the distance, we estimate
masses of the 8 stars by utilising different combinations of seismic and non-seismic inputs.
When introducing a correction to the Δν scaling relation as suggested by stellar models, for
RGB stars we find excellent agreement with the expected masses from isochrone fitting, and
with a distance modulus derived using independent methods. The offset with respect to independent
masses is lower, or comparable with, the uncertainties on the average RGB mass
(4 − 10%, depending on the combination of constraints used). Our results lend confidence to
asteroseismic masses in the metal poor regime. We note that a larger sample will be needed
to allow more stringent tests to be made of systematic uncertainties in all the observables
(both seismic and non-seismic), and to explore the properties of RHB stars, and of different
populations in the cluster.
Large turbulent reservoirs of cold molecular gas around high-redshift starbur...Sérgio Sacani
Starburst galaxies at the peak of cosmic star formation1
are among
the most extreme star-forming engines in the Universe, producing
stars over about 100 million years (ref. 2). The star-formation
rates of these galaxies, which exceed 100 solar masses per year,
require large reservoirs of cold molecular gas3
to be delivered to
their cores, despite strong feedback from stars or active galactic
nuclei4,5
. Consequently, starburst galaxies are ideal for studying the
interplay between this feedback and the growth of a galaxy6
. The
methylidyne cation, CH+, is a most useful molecule for such studies
because it cannot form in cold gas without suprathermal energy
input, so its presence indicates dissipation of mechanical energy7–9
or strong ultraviolet irradiation10,11. Here we report the detection of
CH+ (J=1–0) emission and absorption lines in the spectra of six
lensed starburst galaxies12–15 at redshifts near 2.5. This line has
such a high critical density for excitation that it is emitted only in
very dense gas, and is absorbed in low-density gas10. We find that
the CH+ emission lines, which are broader than 1,000 kilometres
per second, originate in dense shock waves powered by hot galactic
winds. The CH+ absorption lines reveal highly turbulent reservoirs
of cool (about 100 kelvin), low-density gas, extending far (more than
10 kiloparsecs) outside the starburst galaxies (which have radii of
less than 1 kiloparsec). We show that the galactic winds sustain
turbulence in the 10-kiloparsec-scale environments of the galaxies,
processing these environments into multiphase, gravitationally
bound reservoirs. However, the mass outflow rates are found to be
insufficient to balance the star-formation rates. Another mass input
is therefore required for these reservoirs, which could be provided by
ongoing mergers16 or cold-stream accretion17,18. Our results suggest
that galactic feedback, coupled jointly to turbulence and gravity,
extends the starburst phase of a galaxy instead of quenching it
First identification of_direct_collapse_black_holes_candidates_in_the_early_u...Sérgio Sacani
The first black hole seeds, formed when the Universe was younger than ⇠ 500Myr, are recognized
to play an important role for the growth of early (z ⇠ 7) super-massive black holes.
While progresses have been made in understanding their formation and growth, their observational
signatures remain largely unexplored. As a result, no detection of such sources has been
confirmed so far. Supported by numerical simulations, we present a novel photometric method
to identify black hole seed candidates in deep multi-wavelength surveys.We predict that these
highly-obscured sources are characterized by a steep spectrum in the infrared (1.6−4.5μm),
i.e. by very red colors. The method selects the only 2 objects with a robust X-ray detection
found in the CANDELS/GOODS-S survey with a photometric redshift z & 6. Fitting their
infrared spectra only with a stellar component would require unrealistic star formation rates
(& 2000M# yr−1). To date, the selected objects represent the most promising black hole seed
candidates, possibly formed via the direct collapse black hole scenario, with predicted mass
> 105M#. While this result is based on the best photometric observations of high-z sources
available to date, additional progress is expected from spectroscopic and deeper X-ray data.
Upcoming observatories, like the JWST, will greatly expand the scope of this work.
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.
We present spectroscopic observations of the nearby dwarf galaxy AGC 198691. This object is part
of the Survey of H I in Extremely Low-Mass Dwarfs (SHIELD) project, which is a multi-wavelength
study of galaxies with H I masses in the range of 106-107:2 M discovered by the ALFALFA survey.
We have obtained spectra of the lone H II region in AGC 198691 with the new high-throughput
KPNO Ohio State Multi-Object Spectrograph (KOSMOS) on the Mayall 4-m as well as with the Blue
Channel spectrograph on the MMT 6.5-m telescope. These observations enable the measurement of the
temperature-sensitive [O III]4363 line and hence the determination of a \direct" oxygen abundance
for AGC 198691. We nd this system to be an extremely metal-decient (XMD) system with an
oxygen abundance of 12+log(O/H) = 7.02 0.03, making AGC 198691 the lowest-abundance starforming
galaxy known in the local universe. Two of the ve lowest-abundance galaxies known have
been discovered by the ALFALFA blind H I survey; this high yield of XMD galaxies represents a
paradigm shift in the search for extremely metal-poor galaxies.
A nearby yoiung_m_dwarf_with_wide_possibly_planetary_m_ass_companionSérgio Sacani
O objeto de massa planetária J2126, anteriormente pensado como sendo um planeta solitário, orbita sua estrela mãe na maior órbita já descoberta até agora no universo, de acordo com uma equipe de astrônomos liderada pelo Dr. Niall Deacon, da Universidade de Hertfordshire, no Reino Unido.
O J2126, cujo nome completo é 2MASS J21265040-8140293, tem cerca de 13 vezes a massa de Júpiter.
Sua órbita é de aproximadamente 6900 Unidades Astronômicas de distância da sua estrela, a TYC 9486-927-1, uma estrela ativa, de rotação rápida e classificada como sendo do tipo Anã-M.
Essa é uma órbita 6900 vezes maior que a distância da Terra ao Sol, ou seja, aproximadamente 1 trilhão de quilômetros. Nessa sua órbita, o planeta leva 900000 anos para completar uma volta ao redor da sua estrela.
Stellar-like objects with effective temperatures of 2700K and below are referred to as
20 "ultracool dwarfs"1. This heterogeneous group includes both extremely low-mass stars
21 and brown dwarfs (substellar objects not massive enough to sustain hydrogen fusion),
22 and represents about 15% of the stellar-like objects in the vicinity of the Sun2. Based on
23 the small masses and sizes of their protoplanetary disks3,4, core-accretion theory for
24 ultracool dwarfs predicts a large, but heretofore undetected, population of close-in
25 terrestrial planets5, ranging from metal-rich Mercury-sized planets6 to more hospitable
26 volatile-rich Earth-sized planets7. Here we report the discovery of three short-period
27 Earth-sized planets transiting an ultracool dwarf star 12 parsecs away. The inner two
28 planets receive four and two times the irradiation of Earth, respectively, placing them
29 close to the inner edge of the habitable zone of the star8. Eleven orbits remain possible
30 for the third planet based on our data, the most likely resulting in an irradiation
31 significantly smaller than Earth's. The infrared brightness of the host star combined
32 with its Jupiter-like size offer the possibility of constraining the composition and
33 thoroughly characterizing the atmospheric properties of the components of this nearby
34 planetary system, notably to detect potential biosignatures.
Uma grande equipe de astrônomos registrou uma supernova extremamente luminosa numa galáxia massiva a cerca de 3.82 bilhões de anos-luz de distância.
A explosão recém-descoberta, denominada de ASASSN-15Ih, pertence à classe mais luminosa de supernovas, chamada de supernovas superluminosas.
"Ela parece ter originado numa grande galáxia, em contraste com a maioria das supernovas superluminosas, que normalmente se originam em galáxias anãs com formação de estrelas", disse o Dr. Subo Dong, do Kavli Institute for Astronomy and Astrophysics e coautor do artigo publicado na revista Science que descreve a descoberta.
"Nós estimamos o raio efetivo para a galáxia de 7830 anos-luz e uma massa estelar de 200 bilhões de massas solares".
Também conhecida como SN 2015L, a ASASSN-15lh é aproximadamente 200 vezes mais poderosa do que uma típica explosão de supernova do Tipo Ia, cerca de 570 bilhões de vezes mais brilhante do que o nosso Sol, e vinte vezes mais brilhante do que todas as estrelas na nossa galáxia combinadas.
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.
Exocometary gas in_th_hd_181327_debris_ringSérgio Sacani
An increasing number of observations have shown that gaseous debris discs are not an
exception. However, until now we only knew of cases around A stars. Here we present the first
detection of 12CO (2-1) disc emission around an F star, HD 181327, obtained with ALMA
observations at 1.3 mm. The continuum and CO emission are resolved into an axisymmetric
disc with ring-like morphology. Using a Markov chain Monte Carlo method coupled with
radiative transfer calculations we study the dust and CO mass distribution. We find the dust is
distributed in a ring with a radius of 86:0 0:4 AU and a radial width of 23:2 1:0 AU. At
this frequency the ring radius is smaller than in the optical, revealing grain size segregation
expected due to radiation pressure. We also report on the detection of low level continuum
emission beyond the main ring out to 200 AU. We model the CO emission in the non-LTE
regime and we find that the CO is co-located with the dust, with a total CO gas mass ranging
between 1:2 10 6 M and 2:9 10 6 M, depending on the gas kinetic temperature and
collisional partners densities. The CO densities and location suggest a secondary origin, i.e.
released from icy planetesimals in the ring. We derive a CO cometary composition that is
consistent with Solar system comets. Due to the low gas densities it is unlikely that the gas is
shaping the dust distribution.
Beyond the Kuiper Belt Edge: New High Perihelion Trans-Neptunian Objects With...Sérgio Sacani
We are conducting a survey for distant solar system objects beyond the Kuiper
Belt edge ( 50 AU) with new wide-field cameras on the Subaru and CTIO tele-
scopes. We are interested in the orbits of objects that are decoupled from the
giant planet region in order to understand the structure of the outer solar sys-
tem, including whether a massive planet exists beyond a few hundred AU as first
reported in Trujillo and Sheppard (2014). In addition to discovering extreme
trans-Neptunian objects detailed elsewhere, we have found several objects with
high perihelia (q > 40 AU) that differ from the extreme and inner Oort cloud
objects due to their moderate semi-major axes (50 < a < 100 AU) and eccen-
tricities (e . 0.3). Newly discovered objects 2014 FZ71 and 2015 FJ345 have
the third and fourth highest perihelia known after Sedna and 2012 VP113, yet
their orbits are not nearly as eccentric or distant. We found several of these high
perihelion but moderate orbit objects and observe that they are mostly near Nep-
tune mean motion resonances and have significant inclinations (i > 20 degrees).
These moderate objects likely obtained their unusual orbits through combined
interactions with Neptune’s mean motion resonances and the Kozai resonance,
similar to the origin scenarios for 2004 XR190. We also find the distant 2008
ST291 has likely been modified by the MMR+KR mechanism through the 6:1
Neptune resonance. We discuss these moderately eccentric, distant objects along
with some other interesting low inclination outer classical belt objects like 2012
FH84 discovered in our ongoing survey.
[…] Ahora bien; JIMÉNEZ URE, como buen enamorado de la sabiduría, deja evidencias de una remarcada voz cartesiana: «[…] Pero, no soy testigo porque no experimenté el instante de mi creación o fecundación» (Cfr., p. 31). Aquí captamos dos secuencias del Empirismo Metodológico: la experiencia y la fecundación, contrastadas con un término («creación») teológico que deja entrever las raíces cristianas del autor […](Ramón E. Azócar A.)
The completeness-corrected rate of stellar encounters with the Sun from the f...Sérgio Sacani
I report on close encounters of stars to the Sun found in the first Gaia data release (GDR1). Combining Gaia astrometry with radial
velocities of around 320 000 stars drawn from various catalogues, I integrate orbits in a Galactic potential to identify those stars which
come within a few parsecs. Such encounters could influence the solar system, for example through gravitational perturbations of the
Oort cloud. 16 stars are found to come within 2 pc (although a few of these have dubious data). This is fewer than were found in a
similar study based on Hipparcos data, even though the present study has many more candidates. This is partly because I reject stars
with large radial velocity uncertainties (>10 km s−1
), and partly because of missing stars in GDR1 (especially at the bright end). The
closest encounter found is Gl 710, a K dwarf long-known to come close to the Sun in about 1.3 Myr. The Gaia astrometry predict
a much closer passage than pre-Gaia estimates, however: just 16 000 AU (90% confidence interval: 10 000–21 000 AU), which will
bring this star well within the Oort cloud. Using a simple model for the spatial, velocity, and luminosity distributions of stars, together
with an approximation of the observational selection function, I model the incompleteness of this Gaia-based search as a function
of the time and distance of closest approach. Applying this to a subset of the observed encounters (excluding duplicates and stars
with implausibly large velocities), I estimate the rate of stellar encounters within 5 pc averaged over the past and future 5 Myr to be
545±59 Myr−1
. Assuming a quadratic scaling of the rate within some encounter distance (which my model predicts), this corresponds
to 87 ± 9 Myr−1 within 2 pc. A more accurate analysis and assessment will be possible with future Gaia data releases.
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
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
WHERE IS THE FLUX GOING? THE LONG-TERM PHOTOMETRIC VARIABILITY OF BOYAJIAN’S ...Sérgio Sacani
We present ∼ 800 days of photometric monitoring of Boyajian’s Star (KIC 8462852) from the AllSky
Automated Survey for Supernovae (ASAS-SN) and ∼ 4000 days of monitoring from the All Sky
Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian’s Star
has steadily decreased at a rate of 6.3 ± 1.4 mmag yr−1
, such that the star is now 1.5% fainter than it
was in February 2015. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian’s
Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a
monotonic decline. We analyze a sample of ∼ 1000 comparison stars of similar brightness located in
the same ASAS-SN field and demonstrate that the recent fading is significant at & 99.4% confidence.
The 2015 − 2017 dimming rate is consistent with that measured with Kepler data for the time period
from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models
for the star’s behavior proposed to date
Evidence for a_distant_giant_planet_in_the_solar_systemSérgio Sacani
A descoberta de um novo planeta, atualmente não é uma manchete que chama tanto assim a atenção das pessoas. Muito disso, graças ao Telescópio Espacial Kepler, que já descobriu quase 2000 exoplanetas e todo instante uma nova descoberta é anunciada, certo? Mais ou menos, a descoberta anunciada hoje, dia 20 de Janeiro de 2016, é um pouco diferente, pois não se trata de um exoplaneta, e sim de um novo planeta no Sistema Solar, e esse é um fato que intriga os astrônomos a muitos e muitos anos.
Porém, temos que ir com calma com esses anúncios. No artigo aceito para publicação no The Astronomical Journal (artigo no final do post), os autores, Mike Brown e Konstantin Batygin, do Instituto de Tecnologia da Califórnia, apresentaram o que eles dizem ser evidências circunstâncias fortes para a existência de um grande planeta ainda não descoberto, talvez, com uma massa 10 vezes a massa da Terra, orbitando os confins do nosso Sistema Solar, muito além da órbita de Plutão. Os cientistas inferiram sua presença, por meio de anomalias encontradas nas órbitas de seis objetos do chamado Cinturão de Kuiper.
O objeto, que os pesquisadores estão chamando de Planeta Nove, não chega muito perto do Sol, no ponto mais próximo da sua órbita ele fica a 30.5 bilhões de quilômetros, ou seja, cinco vezes a distância entre o Sol e Plutão. Apesar do seu grande tamanho, ele é muito apagado, e por isso ninguém até o momento conseguiu observá-lo.
Não existe ainda uma confirmação observacional da descoberta, mas as evidências são tão fortes que fizeram com que outros especialistas como Chad Trujilo do Observatório Gemini no Havaí e David Nesvorny, do Southwest Research Institute em Boulder no Colorado, ficassem impressionados e bem convencidos de que deve mesmo haver um grande planeta nas fronteiras da nossa vizinhança cósmica.
The canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
We report the discovery of an optical Einstein Ring in the Sculptor constellation,
IAC J010127-334319, in the vicinity of the Sculptor Dwarf Spheroidal Galaxy. It is
an almost complete ring ( 300◦) with a diameter of 4.5 arcsec. The discovery was
made serendipitously from inspecting Dark Energy Camera (DECam) archive imaging
data. Confirmation of the object nature has been obtained by deriving spectroscopic
redshifts for both components, lens and source, from observations at the 10.4 m Gran
Telescopio CANARIAS (GTC) with the spectrograph OSIRIS. The lens, a massive
early-type galaxy, has a redshift of z = 0.581 while the source is a starburst galaxy
with redshift of z = 1.165. The total enclosed mass that produces the lensing effect
has been estimated to be Mtot = (1.86 ± 0.23) · 1012M⊙.
We report the discovery of a new Kepler transiting circumbinary planet (CBP).
This latest addition to the still-small family of CBPs defies the current trend of known
short-period planets orbiting near the stability limit of binary stars. Unlike the previous
discoveries, the planet revolving around the eclipsing binary system Kepler-1647 has
a very long orbital period ( 1100 days) and was at conjunction only twice during
the Kepler mission lifetime. Due to the singular configuration of the system, Kepler-
1647b is not only the longest-period transiting CBP at the time of writing, but also one
of the longest-period transiting planets. With a radius of 1:060:01 RJup it is also the
largest CBP to date. The planet produced three transits in the light-curve of Kepler-
1647 (one of them during an eclipse, creating a syzygy) and measurably perturbed the
times of the stellar eclipses, allowing us to measure its mass to be 1:520:65 MJup.
The planet revolves around an 11-day period eclipsing binary consisting of two Solarmass
stars on a slightly inclined, mildly eccentric (ebin = 0:16), spin-synchronized
orbit. Despite having an orbital period three times longer than Earth’s, Kepler-1647b is
in the conservative habitable zone of the binary star throughout its orbit.
Detection of solar_like_oscillations_in_relies_of_the_milk_way_asteroseismolo...Sérgio Sacani
Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens
of thousands of field stars. Tests against independent estimates of these properties are however
scarce, especially in the metal-poor regime. Here, we report the detection of solar-like
oscillations in 8 stars belonging to the red-giant branch and red-horizontal branch of the globular
cluster M4. The detections were made in photometric observations from the K2 Mission
during its Campaign 2. Making use of independent constraints on the distance, we estimate
masses of the 8 stars by utilising different combinations of seismic and non-seismic inputs.
When introducing a correction to the Δν scaling relation as suggested by stellar models, for
RGB stars we find excellent agreement with the expected masses from isochrone fitting, and
with a distance modulus derived using independent methods. The offset with respect to independent
masses is lower, or comparable with, the uncertainties on the average RGB mass
(4 − 10%, depending on the combination of constraints used). Our results lend confidence to
asteroseismic masses in the metal poor regime. We note that a larger sample will be needed
to allow more stringent tests to be made of systematic uncertainties in all the observables
(both seismic and non-seismic), and to explore the properties of RHB stars, and of different
populations in the cluster.
Large turbulent reservoirs of cold molecular gas around high-redshift starbur...Sérgio Sacani
Starburst galaxies at the peak of cosmic star formation1
are among
the most extreme star-forming engines in the Universe, producing
stars over about 100 million years (ref. 2). The star-formation
rates of these galaxies, which exceed 100 solar masses per year,
require large reservoirs of cold molecular gas3
to be delivered to
their cores, despite strong feedback from stars or active galactic
nuclei4,5
. Consequently, starburst galaxies are ideal for studying the
interplay between this feedback and the growth of a galaxy6
. The
methylidyne cation, CH+, is a most useful molecule for such studies
because it cannot form in cold gas without suprathermal energy
input, so its presence indicates dissipation of mechanical energy7–9
or strong ultraviolet irradiation10,11. Here we report the detection of
CH+ (J=1–0) emission and absorption lines in the spectra of six
lensed starburst galaxies12–15 at redshifts near 2.5. This line has
such a high critical density for excitation that it is emitted only in
very dense gas, and is absorbed in low-density gas10. We find that
the CH+ emission lines, which are broader than 1,000 kilometres
per second, originate in dense shock waves powered by hot galactic
winds. The CH+ absorption lines reveal highly turbulent reservoirs
of cool (about 100 kelvin), low-density gas, extending far (more than
10 kiloparsecs) outside the starburst galaxies (which have radii of
less than 1 kiloparsec). We show that the galactic winds sustain
turbulence in the 10-kiloparsec-scale environments of the galaxies,
processing these environments into multiphase, gravitationally
bound reservoirs. However, the mass outflow rates are found to be
insufficient to balance the star-formation rates. Another mass input
is therefore required for these reservoirs, which could be provided by
ongoing mergers16 or cold-stream accretion17,18. Our results suggest
that galactic feedback, coupled jointly to turbulence and gravity,
extends the starburst phase of a galaxy instead of quenching it
First identification of_direct_collapse_black_holes_candidates_in_the_early_u...Sérgio Sacani
The first black hole seeds, formed when the Universe was younger than ⇠ 500Myr, are recognized
to play an important role for the growth of early (z ⇠ 7) super-massive black holes.
While progresses have been made in understanding their formation and growth, their observational
signatures remain largely unexplored. As a result, no detection of such sources has been
confirmed so far. Supported by numerical simulations, we present a novel photometric method
to identify black hole seed candidates in deep multi-wavelength surveys.We predict that these
highly-obscured sources are characterized by a steep spectrum in the infrared (1.6−4.5μm),
i.e. by very red colors. The method selects the only 2 objects with a robust X-ray detection
found in the CANDELS/GOODS-S survey with a photometric redshift z & 6. Fitting their
infrared spectra only with a stellar component would require unrealistic star formation rates
(& 2000M# yr−1). To date, the selected objects represent the most promising black hole seed
candidates, possibly formed via the direct collapse black hole scenario, with predicted mass
> 105M#. While this result is based on the best photometric observations of high-z sources
available to date, additional progress is expected from spectroscopic and deeper X-ray data.
Upcoming observatories, like the JWST, will greatly expand the scope of this work.
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.
We present spectroscopic observations of the nearby dwarf galaxy AGC 198691. This object is part
of the Survey of H I in Extremely Low-Mass Dwarfs (SHIELD) project, which is a multi-wavelength
study of galaxies with H I masses in the range of 106-107:2 M discovered by the ALFALFA survey.
We have obtained spectra of the lone H II region in AGC 198691 with the new high-throughput
KPNO Ohio State Multi-Object Spectrograph (KOSMOS) on the Mayall 4-m as well as with the Blue
Channel spectrograph on the MMT 6.5-m telescope. These observations enable the measurement of the
temperature-sensitive [O III]4363 line and hence the determination of a \direct" oxygen abundance
for AGC 198691. We nd this system to be an extremely metal-decient (XMD) system with an
oxygen abundance of 12+log(O/H) = 7.02 0.03, making AGC 198691 the lowest-abundance starforming
galaxy known in the local universe. Two of the ve lowest-abundance galaxies known have
been discovered by the ALFALFA blind H I survey; this high yield of XMD galaxies represents a
paradigm shift in the search for extremely metal-poor galaxies.
A nearby yoiung_m_dwarf_with_wide_possibly_planetary_m_ass_companionSérgio Sacani
O objeto de massa planetária J2126, anteriormente pensado como sendo um planeta solitário, orbita sua estrela mãe na maior órbita já descoberta até agora no universo, de acordo com uma equipe de astrônomos liderada pelo Dr. Niall Deacon, da Universidade de Hertfordshire, no Reino Unido.
O J2126, cujo nome completo é 2MASS J21265040-8140293, tem cerca de 13 vezes a massa de Júpiter.
Sua órbita é de aproximadamente 6900 Unidades Astronômicas de distância da sua estrela, a TYC 9486-927-1, uma estrela ativa, de rotação rápida e classificada como sendo do tipo Anã-M.
Essa é uma órbita 6900 vezes maior que a distância da Terra ao Sol, ou seja, aproximadamente 1 trilhão de quilômetros. Nessa sua órbita, o planeta leva 900000 anos para completar uma volta ao redor da sua estrela.
Stellar-like objects with effective temperatures of 2700K and below are referred to as
20 "ultracool dwarfs"1. This heterogeneous group includes both extremely low-mass stars
21 and brown dwarfs (substellar objects not massive enough to sustain hydrogen fusion),
22 and represents about 15% of the stellar-like objects in the vicinity of the Sun2. Based on
23 the small masses and sizes of their protoplanetary disks3,4, core-accretion theory for
24 ultracool dwarfs predicts a large, but heretofore undetected, population of close-in
25 terrestrial planets5, ranging from metal-rich Mercury-sized planets6 to more hospitable
26 volatile-rich Earth-sized planets7. Here we report the discovery of three short-period
27 Earth-sized planets transiting an ultracool dwarf star 12 parsecs away. The inner two
28 planets receive four and two times the irradiation of Earth, respectively, placing them
29 close to the inner edge of the habitable zone of the star8. Eleven orbits remain possible
30 for the third planet based on our data, the most likely resulting in an irradiation
31 significantly smaller than Earth's. The infrared brightness of the host star combined
32 with its Jupiter-like size offer the possibility of constraining the composition and
33 thoroughly characterizing the atmospheric properties of the components of this nearby
34 planetary system, notably to detect potential biosignatures.
Uma grande equipe de astrônomos registrou uma supernova extremamente luminosa numa galáxia massiva a cerca de 3.82 bilhões de anos-luz de distância.
A explosão recém-descoberta, denominada de ASASSN-15Ih, pertence à classe mais luminosa de supernovas, chamada de supernovas superluminosas.
"Ela parece ter originado numa grande galáxia, em contraste com a maioria das supernovas superluminosas, que normalmente se originam em galáxias anãs com formação de estrelas", disse o Dr. Subo Dong, do Kavli Institute for Astronomy and Astrophysics e coautor do artigo publicado na revista Science que descreve a descoberta.
"Nós estimamos o raio efetivo para a galáxia de 7830 anos-luz e uma massa estelar de 200 bilhões de massas solares".
Também conhecida como SN 2015L, a ASASSN-15lh é aproximadamente 200 vezes mais poderosa do que uma típica explosão de supernova do Tipo Ia, cerca de 570 bilhões de vezes mais brilhante do que o nosso Sol, e vinte vezes mais brilhante do que todas as estrelas na nossa galáxia combinadas.
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.
Exocometary gas in_th_hd_181327_debris_ringSérgio Sacani
An increasing number of observations have shown that gaseous debris discs are not an
exception. However, until now we only knew of cases around A stars. Here we present the first
detection of 12CO (2-1) disc emission around an F star, HD 181327, obtained with ALMA
observations at 1.3 mm. The continuum and CO emission are resolved into an axisymmetric
disc with ring-like morphology. Using a Markov chain Monte Carlo method coupled with
radiative transfer calculations we study the dust and CO mass distribution. We find the dust is
distributed in a ring with a radius of 86:0 0:4 AU and a radial width of 23:2 1:0 AU. At
this frequency the ring radius is smaller than in the optical, revealing grain size segregation
expected due to radiation pressure. We also report on the detection of low level continuum
emission beyond the main ring out to 200 AU. We model the CO emission in the non-LTE
regime and we find that the CO is co-located with the dust, with a total CO gas mass ranging
between 1:2 10 6 M and 2:9 10 6 M, depending on the gas kinetic temperature and
collisional partners densities. The CO densities and location suggest a secondary origin, i.e.
released from icy planetesimals in the ring. We derive a CO cometary composition that is
consistent with Solar system comets. Due to the low gas densities it is unlikely that the gas is
shaping the dust distribution.
Beyond the Kuiper Belt Edge: New High Perihelion Trans-Neptunian Objects With...Sérgio Sacani
We are conducting a survey for distant solar system objects beyond the Kuiper
Belt edge ( 50 AU) with new wide-field cameras on the Subaru and CTIO tele-
scopes. We are interested in the orbits of objects that are decoupled from the
giant planet region in order to understand the structure of the outer solar sys-
tem, including whether a massive planet exists beyond a few hundred AU as first
reported in Trujillo and Sheppard (2014). In addition to discovering extreme
trans-Neptunian objects detailed elsewhere, we have found several objects with
high perihelia (q > 40 AU) that differ from the extreme and inner Oort cloud
objects due to their moderate semi-major axes (50 < a < 100 AU) and eccen-
tricities (e . 0.3). Newly discovered objects 2014 FZ71 and 2015 FJ345 have
the third and fourth highest perihelia known after Sedna and 2012 VP113, yet
their orbits are not nearly as eccentric or distant. We found several of these high
perihelion but moderate orbit objects and observe that they are mostly near Nep-
tune mean motion resonances and have significant inclinations (i > 20 degrees).
These moderate objects likely obtained their unusual orbits through combined
interactions with Neptune’s mean motion resonances and the Kozai resonance,
similar to the origin scenarios for 2004 XR190. We also find the distant 2008
ST291 has likely been modified by the MMR+KR mechanism through the 6:1
Neptune resonance. We discuss these moderately eccentric, distant objects along
with some other interesting low inclination outer classical belt objects like 2012
FH84 discovered in our ongoing survey.
[…] Ahora bien; JIMÉNEZ URE, como buen enamorado de la sabiduría, deja evidencias de una remarcada voz cartesiana: «[…] Pero, no soy testigo porque no experimenté el instante de mi creación o fecundación» (Cfr., p. 31). Aquí captamos dos secuencias del Empirismo Metodológico: la experiencia y la fecundación, contrastadas con un término («creación») teológico que deja entrever las raíces cristianas del autor […](Ramón E. Azócar A.)
We report the discovery of spiral galaxies that are as optically luminous as elliptical brightest cluster
galaxies, with r-band monochromatic luminosity Lr = 8 14L (4:3 7:5 1044 erg s 1). These
super spiral galaxies are also giant and massive, with diameter D = 57 134 kpc and stellar mass
Mstars = 0:3 3:4 1011M. We nd 53 super spirals out of a complete sample of 1616 SDSS
galaxies with redshift z < 0:3 and Lr > 8L. The closest example is found at z = 0:089. We use
existing photometry to estimate their stellar masses and star formation rates (SFRs). The SDSS
and WISE colors are consistent with normal star-forming spirals on the blue sequence. However, the
extreme masses and rapid SFRs of 5 65M yr 1 place super spirals in a sparsely populated region
of parameter space, above the star-forming main sequence of disk galaxies. Super spirals occupy a
diverse range of environments, from isolation to cluster centers. We nd four super spiral galaxy
systems that are late-stage major mergers{a possible clue to their formation. We suggest that super
spirals are a remnant population of unquenched, massive disk galaxies. They may eventually become
massive lenticular galaxies after they are cut o from their gas supply and their disks fade.
The harps n-rocky_planet_search_hd219134b_transiting_rocky_planetSérgio Sacani
Usando o espectrógrafo HARPS-N acoplado ao Telescopio Nazionale Galileo no Observatório de Roque de Los Muchachos, nas Ilhas Canárias, os astrônomos descobriram três exoplanetas, classificados como Super-Terras e um gigante gasoso orbitando uma estrela próxima, chamada de HD 219134.
A HD 219134, também conhecida como HR 8832 é uma estrela do tipo anã-K de quinta magnitude, localizada a aproximadamente 21 anos-luz de distância da Terra, na constelação de Cassiopeia.
A estrela é levemente mais fria e menos massiva que o nosso sol. Ela é tão brilhante que pode ser observada a olho nu.
O sistema planetário HD 219134, abriga um planeta gigante gasoso externo e três planetas internos classificados como super-Terras, um dos quais transita em frente à estrela.
Four new planets_around_giant_stars_and_the_mass_metallicity_correlation_of_p...Sérgio Sacani
Exoplanet searches have revealed interesting correlations between the stellar properties and the occurrence rate of planets.
In particular, different independent surveys have demonstrated that giant planets are preferentially found around metal-rich stars and
that their fraction increases with the stellar mass.
Aims. During the past six years, we have conducted a radial velocity follow-up program of 166 giant stars, to detect substellar
companions, and characterizing their orbital properties. Using this information, we aim to study the role of the stellar evolution in
the orbital parameters of the companions, and to unveil possible correlations between the stellar properties and the occurrence rate of
giant planets.
Methods. We have taken multi-epoch spectra using FEROS and CHIRON for all of our targets, from which we have computed
precision radial velocities and we have derived atmospheric and physical parameters. Additionally, velocities computed from UCLES
spectra are presented here. By studying the periodic radial velocity signals, we have detected the presence of several substellar
companions.
Results. We present four new planetary systems around the giant stars HIP8541, HIP74890, HIP84056 and HIP95124. Additionally,
we study the correlation between the occurrence rate of giant planets with the stellar mass and metallicity of our targets. We find that
giant planets are more frequent around metal-rich stars, reaching a peak in the detection of f = 16.7+15.5
−5.9 % around stars with [Fe/H] ∼
0.35 dex. Similarly, we observe a positive correlation of the planet occurrence rate with the stellar mass, between M⋆∼ 1.0 - 2.1 M⊙ ,
with a maximum of f = 13.0+10.1
−4.2 %, at M⋆= 2.1 M⊙ .
Conclusions. We conclude that giant planets are preferentially formed around metal-rich stars. Also, we conclude that they are more
efficiently formed around more massive stars, in the stellar mass range of ∼ 1.0 - 2.1 M⊙ . These observational results confirm previous
findings for solar-type and post-MS hosting stars, and provide further support to the core-accretion formation model.
Uma espetacular colisão de galáxias foi descoberta além da Via Láctea. O sistema mais próximo já descoberto, a identificação foi anunciada por uma equipe de astrônomos liderada pelo Professor Quentin Parker da Universidade de Hong Kong e pelo Professor Albert Zijlstra na Universidade de Manchester.
A galáxia está a 30 milhões de anos-luz de distância, o que significa que ela é relativamente próxima. Ela foi chamada de Roda de Kathryn, em homenagem à sua semelhança com o famoso fogo de artifício e também em homenagem à esposa do coautor do trabalho.
Esses sistemas são muito raros e nascem da colisão entre duas galáxias de tamanhos similares. As ondas de choque geradas na colisão comprimem o reservatório de gás em cada galáxia e disparam a formação de novas estrelas. Isso cria um espetacular anel de intensa emissão, e ilumina o sistema, do mesmo modo que a Roda Catherine ilumina a noite num show de fogos de artifício.
As galáxias crescem através de colisões, mas é raro registrar esse processo acontecendo, e é extremamente raro ver o anel da colisão em progresso. Pouco mais de 20 sistemas com anéis completos são conhecidos.
Uma equipe formada por astrônomos de Israel, da Europa, da Coreia e dos EUA, anunciou a descoberta de um exoplaneta gigante gasoso circumbinário, na zona habitável de seu par de estrelas, uma ocorrência surpreendentemente comum para os exoplanetas circumbinários descobertos pela missão Kepler/K2 da NASA.
Lembrando o planeta da ficção, Tatooine, exoplanetas circumbinários orbitam duas estrelas e assim têm dois sóis em seu céu.
O exoplaneta circumbinário, recém-descoberto, denominado de Kepler-453b, leva 240.5 dias para orbitar suas estrelas, enquanto as estrelas orbitam uma com relação a outra a cada 27.3 dias.
A estrela maior, a Kepler-453A, é similar ao nosso Sol, contendo 94% da massa do Sol, enquanto que a estrela menor, a Kepler-453B, tem cerca de 20% da massa e é mais fria e mais apagada.
O sistema binário, localiza-se na constelação de Lyra, e está a aproximadamente 1400 anos-luz de distância da Terra. Estima-se que esse sistema tenha entre 1 e 2 bilhões de anos de vida, sendo bem mais novo que o nosso Sistema Solar.
Também conhecido como KIC 9632895b, o Kepler-453b tem um raio 6.2 vezes maior que o da Terra. Sua massa não foi medida nos dados atuais, mas provavelmente ele deve ter cerca de 16 vezes a massa da Terra.
De acordo com os astrônomos, o Kepler-453b, é o terceiro planeta circumbinário da missão Kepler, descoberto na zona habitável de um par de estrelas.
Devido ao seu tamanho, e a sua natureza gasosa, o planeta pouco provavelmente deve abrigar a vida como nós a conhecemos. Contudo, ele pode, como os gigantes gasosos do Sistema Solar, ter grandes luas, e essas luas poderiam ser habitáveis. Sua órbita se manterá estável por 10 milhões de anos, aumentando a possibilidade da vida se formar nas suas luas.
Com o número de exoplanetas circumbinários conhecidos agora em dez, os cientistas podem começar a comparar diferentes sistemas e procurar uma tendência. Os sistemas tendem a ser bem compactos e podem aparecer num grande número de configurações.
Uma vez pensados como sendo raros e até mesmo impossíveis de existir, essa e outras descobertas do Kepler, confirmam que esses planetas são comuns na nossa Via Láctea.
“A diversidade e complexidade desses sistemas circumbinários é algo maravilhoso. Cada novo planeta circumbinário, é uma joia, revelando algo inesperado e desafiador”, disse o Prof. William Welsh da Universidade Estadual de San Diego, e o primeiro autor do artigo que descreve a descoberta, publicado no Astrophysical Journal.
Fonte:
http://www.sci-news.com/astronomy/science-kepler453b-circumbinary-exoplanet-03117.html
Direct Measure of Radiative And Dynamical Properties Of An Exoplanet AtmosphereSérgio Sacani
Two decades after the discovery of 51Pegb, the formation processes and atmospheres of short-period gas giants
remain poorly understood. Observations of eccentric systems provide key insights on those topics as they can
illuminate how a planet’s atmosphere responds to changes in incident flux. We report here the analysis of multi-day
multi-channel photometry of the eccentric (e ~ 0.93) hot Jupiter HD80606b obtained with the Spitzer Space
Telescope. The planet’s extreme eccentricity combined with the long coverage and exquisite precision of new
periastron-passage observations allow us to break the degeneracy between the radiative and dynamical timescales
of HD80606b’s atmosphere and constrain its global thermal response. Our analysis reveals that the atmospheric
layers probed heat rapidly (∼4 hr radiative timescale) from<500 to 1400 K as they absorb ~20% of the incoming
stellar flux during the periastron passage, while the planet’s rotation period is 93 35
85
-
+ hr, which exceeds the predicted
pseudo-synchronous period (40 hr).
Key words: methods: numerical – planet–star interactions – planets and satellites: atmospheres – planets and
satellites: dynamical evolution and stability – planets and satellites: individual (HD 80606 b) – techniques:
photometric
ULTRAVIOLET SIGNPOSTS OF RESONANT DYNAMICS IN THE STARBURST-RINGED Sab GALAXY...Sérgio Sacani
The dynamic orchestration of star-birth activity in the starburst-ringed galaxy M94 (NGC 4736) is
investigated using images from the Ultraviolet Imaging Telescope (UIT ; far-ultraviolet [FUV] band),
Hubble Space Telescope (HST ; near-ultraviolet [NUV] band), Kitt Peak 0.9 m telescope (Ha, R, and I
bands), and Palomar 5 m telescope (B band), along with spectra from the International Ultraviolet
Explorer (IUE) and the Lick 1 m telescope. The wide-Ðeld UIT image shows FUV emission from (1) an
elongated nucleus, (2) a di†use inner disk, where Ha is observed in absorption, (3) a bright inner ring of
H II regions at the perimeter of the inner disk (R\ 48A \ 1.1 kpc), and (4) two 500 pc size knots of hot
stars exterior to the ring on diametrically opposite sides of the nucleus (R\ 130A \ 2.9 kpc). The HST
Faint Object Camera image resolves the NUV emission from the nuclear region into a bright core and a
faint 20A long ““ minibar ÏÏ at a position angle of 30¡. Optical and IUE spectroscopy of the nucleus and
di†use inner disk indicates a D107È108 yr old stellar population from low-level star-birth activity
blended with some LINER activity. Analysis of the Ha-, FUV-, NUV-, B-, R-, and I-band emissions,
along with other observed tracers of stars and gas in M94, indicates that most of the star formation is
being orchestrated via ring-bar dynamics, involving the nuclear minibar, inner ring, oval disk, and outer
ring. The inner starburst ring and bisymmetric knots at intermediate radius, in particular, argue for barmediated resonances as the primary drivers of evolution in M94 at the present epoch. Similar processes
may be governing the evolution of the ““ core-dominated ÏÏ galaxies that have been observed at high redshift. The gravitationally lensed ““ Pretzel Galaxy ÏÏ (0024]1654) at a redshift of D1.5 provides an important precedent in this regard.
Artigo descreve a descoberta de um sistema de anéis 200 vezes maior do que o sistema de anéis de Saturno num exoplaneta orbitando a jovem estrela J1407
Eccentricity from transit_photometry_small_planets_in_kepler_multi_planet_sys...Sérgio Sacani
Artigo descreve estudo que mostra que a órbita dos exoplanetas terrestres são na sua maioria órbitas circulares, o que é bom para se procurar por vida e o que vem causando uma revolução no entendimento sobre os sistemas de exoplanteas.
The Possible Tidal Demise of Kepler’s First Planetary SystemSérgio Sacani
We present evidence of tidally-driven inspiral in the Kepler-1658 (KOI-4) system, which consists of a giant planet
(1.1RJ, 5.9MJ) orbiting an evolved host star (2.9Re, 1.5Me). Using transit timing measurements from Kepler,
Palomar/WIRC, and TESS, we show that the orbital period of Kepler-1658b appears to be decreasing at a rate = -
+ P 131 22
20 ms yr−1
, corresponding to an infall timescale P P » 2.5 Myr. We consider other explanations for the
data including line-of-sight acceleration and orbital precession, but find them to be implausible. The observed
period derivative implies a tidal quality factor
¢ = ´ -
+ Q 2.50 10 0.62
0.85 4, in good agreement with theoretical
predictions for inertial wave dissipation in subgiant stars. Additionally, while it probably cannot explain the entire
inspiral rate, a small amount of planetary dissipation could naturally explain the deep optical eclipse observed for
the planet via enhanced thermal emission. As the first evolved system with detected inspiral, Kepler-1658 is a new
benchmark for understanding tidal physics at the end of the planetary life cycle
Artigo descreve a descoberta do exoplaneta HATS-6b, um exoplaneta parecido com Saturno, porém pesado como Júpiter ao redor de uma estrela anã-M, o tipo de estrela mais abundante na nossa galáxia.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
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.
X-rays from a Central “Exhaust Vent” of the Galactic Center ChimneySérgio Sacani
Using deep archival observations from the Chandra X-ray Observatory, we present an analysis of
linear X-ray-emitting features located within the southern portion of the Galactic center chimney,
and oriented orthogonal to the Galactic plane, centered at coordinates l = 0.08◦
, b = −1.42◦
. The
surface brightness and hardness ratio patterns are suggestive of a cylindrical morphology which may
have been produced by a plasma outflow channel extending from the Galactic center. Our fits of the
feature’s spectra favor a complex two-component model consisting of thermal and recombining plasma
components, possibly a sign of shock compression or heating of the interstellar medium by outflowing
material. Assuming a recombining plasma scenario, we further estimate the cooling timescale of this
plasma to be on the order of a few hundred to thousands of years, leading us to speculate that a
sequence of accretion events onto the Galactic Black Hole may be a plausible quasi-continuous energy
source to sustain the observed morphology
Richard's entangled aventures in wonderlandRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
(May 29th, 2024) Advancements in Intravital Microscopy- Insights for Preclini...Scintica Instrumentation
Intravital microscopy (IVM) is a powerful tool utilized to study cellular behavior over time and space in vivo. Much of our understanding of cell biology has been accomplished using various in vitro and ex vivo methods; however, these studies do not necessarily reflect the natural dynamics of biological processes. Unlike traditional cell culture or fixed tissue imaging, IVM allows for the ultra-fast high-resolution imaging of cellular processes over time and space and were studied in its natural environment. Real-time visualization of biological processes in the context of an intact organism helps maintain physiological relevance and provide insights into the progression of disease, response to treatments or developmental processes.
In this webinar we give an overview of advanced applications of the IVM system in preclinical research. IVIM technology is a provider of all-in-one intravital microscopy systems and solutions optimized for in vivo imaging of live animal models at sub-micron resolution. The system’s unique features and user-friendly software enables researchers to probe fast dynamic biological processes such as immune cell tracking, cell-cell interaction as well as vascularization and tumor metastasis with exceptional detail. This webinar will also give an overview of IVM being utilized in drug development, offering a view into the intricate interaction between drugs/nanoparticles and tissues in vivo and allows for the evaluation of therapeutic intervention in a variety of tissues and organs. This interdisciplinary collaboration continues to drive the advancements of novel therapeutic strategies.
This pdf is about the Schizophrenia.
For more details visit on YouTube; @SELF-EXPLANATORY;
https://www.youtube.com/channel/UCAiarMZDNhe1A3Rnpr_WkzA/videos
Thanks...!
The increased availability of biomedical data, particularly in the public domain, offers the opportunity to better understand human health and to develop effective therapeutics for a wide range of unmet medical needs. However, data scientists remain stymied by the fact that data remain hard to find and to productively reuse because data and their metadata i) are wholly inaccessible, ii) are in non-standard or incompatible representations, iii) do not conform to community standards, and iv) have unclear or highly restricted terms and conditions that preclude legitimate reuse. These limitations require a rethink on data can be made machine and AI-ready - the key motivation behind the FAIR Guiding Principles. Concurrently, while recent efforts have explored the use of deep learning to fuse disparate data into predictive models for a wide range of biomedical applications, these models often fail even when the correct answer is already known, and fail to explain individual predictions in terms that data scientists can appreciate. These limitations suggest that new methods to produce practical artificial intelligence are still needed.
In this talk, I will discuss our work in (1) building an integrative knowledge infrastructure to prepare FAIR and "AI-ready" data and services along with (2) neurosymbolic AI methods to improve the quality of predictions and to generate plausible explanations. Attention is given to standards, platforms, and methods to wrangle knowledge into simple, but effective semantic and latent representations, and to make these available into standards-compliant and discoverable interfaces that can be used in model building, validation, and explanation. Our work, and those of others in the field, creates a baseline for building trustworthy and easy to deploy AI models in biomedicine.
Bio
Dr. Michel Dumontier is the Distinguished Professor of Data Science at Maastricht University, founder and executive director of the Institute of Data Science, and co-founder of the FAIR (Findable, Accessible, Interoperable and Reusable) data principles. His research explores socio-technological approaches for responsible discovery science, which includes collaborative multi-modal knowledge graphs, privacy-preserving distributed data mining, and AI methods for drug discovery and personalized medicine. His work is supported through the Dutch National Research Agenda, the Netherlands Organisation for Scientific Research, Horizon Europe, the European Open Science Cloud, the US National Institutes of Health, and a Marie-Curie Innovative Training Network. He is the editor-in-chief for the journal Data Science and is internationally recognized for his contributions in bioinformatics, biomedical informatics, and semantic technologies including ontologies and linked data.
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
Evidence for reflected_lightfrom_the_most_eccentric_exoplanet_known
1. arXiv:1511.08679v4[astro-ph.EP]12Mar2016
Submitted for publication in the Astrophysical Journal
Preprint typeset using LATEX style emulateapj v. 5/2/11
EVIDENCE FOR REFLECTED LIGHT FROM THE MOST ECCENTRIC EXOPLANET KNOWN
Stephen R. Kane1
, Robert A. Wittenmyer2,3,4
, Natalie R. Hinkel1,5
, Arpita Roy6,7
, Suvrath Mahadevan6,7
, Diana
Dragomir8
, Jaymie M. Matthews9
, Gregory W. Henry10
, Abhijit Chakraborty11
, Tabetha S. Boyajian12
, Jason
T. Wright6,7
, David R. Ciardi13
, Debra A. Fischer12
, R. Paul Butler14
, C.G. Tinney2,3
, Brad D. Carter4
, Hugh
R.A. Jones15
, Jeremy Bailey2,3
, Simon J. O’Toole16
Submitted for publication in the Astrophysical Journal
ABSTRACT
Planets in highly eccentric orbits form a class of objects not seen within our Solar System. The most
extreme case known amongst these objects is the planet orbiting HD 20782, with an orbital period of
597 days and an eccentricity of 0.96. Here we present new data and analysis for this system as part of
the Transit Ephemeris Refinement and Monitoring Survey (TERMS). We obtained CHIRON spectra
to perform an independent estimation of the fundamental stellar parameters. New radial velocities
from AAT and PARAS observations during periastron passage greatly improve our knowledge of
the eccentric nature of the orbit. The combined analysis of our Keplerian orbital and Hipparcos
astrometry show that the inclination of the planetary orbit is > 1.22◦
, ruling out stellar masses for
the companion. Our long-term robotic photometry show that the star is extremely stable over long
timescales. Photometric monitoring of the star during predicted transit and periastron times using
MOST rule out a transit of the planet and reveal evidence of phase variations during periastron. These
possible photometric phase variations may be caused by reflected light from the planet’s atmosphere
and the dramatic change in star–planet separation surrounding the periastron passage.
Subject headings: planetary systems – techniques: photometric – techniques: radial velocities – stars:
individual (HD 20782)
1. INTRODUCTION
skane@sfsu.edu
1 Department of Physics & Astronomy, San Francisco State
University, 1600 Holloway Avenue, San Francisco, CA 94132,
USA
2 School of Physics, University of New South Wales, Sydney,
NSW 2052, Australia
3 Australian Center for Astrobiology, University of New South
Wales, Sydney, NSW 2052, Australia
4 Computational Engineering and Science Research Centre,
University of Southern Queensland, Toowoomba, Queensland
4350, Australia
5 School of Earth & Space Exploration, Arizona State Univer-
sity, Tempe, AZ 85287, USA
6 Department of Astronomy and Astrophysics, Pennsylvania
State University, 525 Davey Laboratory, University Park, PA
16802, USA
7 Center for Exoplanets & Habitable Worlds, Pennsylvania
State University, 525 Davey Laboratory, University Park, PA
16802, USA
8 Las Cumbres Observatory Global Telescope Network, 6740
Cortona Drive, Suite 102, Goleta, CA 93117, USA
9 Department of Physics and Astronomy, University of British
Columbia, Vancouver, BC V6T1Z1, Canada
10 Center of Excellence in Information Systems, Tennessee
State University, 3500 John A. Merritt Blvd., Box 9501,
Nashville, TN 37209, USA
11 Division of Astronomy, Physical Research Laboratory,
Navrangpura, Ahmedabad 380009, India
12 Department of Astronomy, Yale University, New Haven, CT
06511, USA
13 NASA Exoplanet Science Institute, Caltech, MS 100-22, 770
South Wilson Avenue, Pasadena, CA 91125, USA
14 Department of Terrestrial Magnetism, Carnegie Institution
of Washington, 5241 Broad Branch Road, NW, Washington, DC
20015-1305, USA
15 University of Hertfordshire, Centre for Astrophysics Re-
search, Science and Technology Research Institute, College Lane,
AL10 9AB, Hatfield, UK
16 Australian Astronomical Observatory, PO Box 915, North
Ryde, NSW 1670, Australia
Exoplanetary system architectures have revealed nu-
merous surprises since the first exoplanets were discov-
ered. One of the earliest surprises was the discovery of
exoplanets in highly eccentric orbits, for which there is
no analog in the Solar System. These eccentric orbits
were discovered for giant planets, such as HD 114762b
(Latham et al. 1989; Kane et al. 2011) and 70 Vir b
(Marcy & Butler 1996; Kane et al. 2015) with eccentric-
ities of 0.33 and 0.40 respectively. Since those early
discoveries, eccentric planets have presented a signifi-
cant challenge for formation theories to account for the
components of planet-planet scattering (Chatterjee et al.
2008; Petrovich et al. 2014) and tidal circularization
(Pont et al. 2011). Such planets tend to be discovered
with the radial velocity (RV) technique since the obser-
vations are able to sample the entire Keplerian planetary
orbit. Subsequent investigations of the eccentricity dis-
tribution of planetary orbits that take Kepler transiting
exoplanet discoveries into account show that small plan-
ets in multi-planet systems are more likely to have low
eccentricities (Kane et al. 2012; Van Eylen & Albrecht
2015). The discovery and characterization of eccentric
orbits is an on-going effort to understand the evolution-
ary history of these fascinating systems.
A particularly eccentric exoplanet was discovered by
Jones et al. (2006) orbiting the star HD 20782. With a
minimum mass twice that of Jupiter and an orbital pe-
riod of 597 days, the planet is typical of high-eccentricity
planets. The orbit was further revised by O’Toole et al.
(2009) and shown to have an eccentricity as high as 0.97,
making it the highest eccentricity exoplanet yet discov-
ered. However, data during periastron passage is diffi-
cult to obtain for such systems since the RV variation
predominantly occurs during a very small fraction of the
orbital phase. The star continued to be monitored by
2. 2 Stephen R. Kane et al.
the Transit Ephemeris Refinement and Monitoring Sur-
vey (TERMS) to improve the orbital parameters of the
system (Kane et al. 2009). Such orbital refinement may
be used to predict and observe events that occur dur-
ing particular periods of the orbit, such as planetary
transits (Kane & von Braun 2008) or phase variations
(Kane & Gelino 2010).
Here we present new results for the HD 20782 system,
including RVs that sample several periastron passages
and establish the planet as the most eccentric known ex-
oplanet. Follow-up photometry from both ground-based
and space-based telescopes rule out a transit of the planet
and show evidence of phase variations due to reflected
light from the planet close to periastron passage. Sec-
tion 2 provides background information and discusses the
science motivation for studying the system. Section 3
presents analysis of new CHIRON spectra and the re-
sulting fundamental parameters of the host star as well
as stellar abundances. New RV data are combined with
those published in Section 4 and a new Keplerian orbit
for the planet is produced. Section 5 describes the use of
Hipparcos astrometry to constrain the orbital inclination
of the planet. Section 6 discusses the transit prospects for
the system and the effects of both orbital eccentricity and
inclination. Section 7 presents the ground-based photom-
etry and an estimate of the stellar rotation period. Data
from MOST are used during the transit/periastron win-
dow to rule out a transit and also reveal the potential
presence of a reflected light signature of the planet as
it passes through periastron passage. We discuss future
observing opportunities and make concluding remarks in
Section 8.
2. SCIENCE MOTIVATION
The eccentricity distribution of exoplanets has a well-
defined shape whereby the orbits diverge from circular
beyond a semi-major axis of ∼ 0.1 AU (Butler et al.
2006; Kane 2013), inside of which tidal circularization
tends to force low eccentricity (Goldreich & Soter 1966;
Pont et al. 2011). The observed eccentricity distribution
is a clear indicator of formation processes that are de-
pendent upon initial system architectures, in particular
planet-planet scattering. Wide binaries may inadver-
tantly create a more suitable environment for the forma-
tion of highly-eccentric planetary orbits through gravi-
tational perturbations from the companion star and the
triggering of planetary ejections (Kaib et al. 2013).
HD 20782 is part of a wide binary with HD 20781
having a projected separation of 9,000 AU, recently de-
scribed by Mack et al. (2014). The known planet orbit-
ing HD 20782 lies at the very top of the exoplanet ec-
centricity distribution, though RV measurements during
the crucial periastron passage were relatively rare. The
extreme nature of the planet’s orbital eccentricity may
be seen in Figure 1, where the orbit is described using
our expanded dataset (see Section 4).
Our further investigations of this system are primar-
ily motivated by a better characterization of the plane-
tary orbit and performing follow-up observations at key
orbital phases that can help to understand the nature
of the planet. It is also important to establish that
the secondary object is indeed a planet since a face-
on orbital orientation would make it consistent with
the eccentricity distribution of spectroscopic binaries
Fig. 1.— A top-down view of the HD 20782 system based on
data described in this paper. The Keplerian orbit of the planet,
shown as a solid line, is depicted using the new parameters from
Table 4. The orbits of the Solar System planets (dashed lines) are
shown for comparison.
(Meibom & Mathieu 2005; Mazeh 2008).
The orbital orientation depicted in Figure 1 shows
that the star–planet separation along the line of sight
to the observer is quite small, despite the ∼18 month
orbital period. This yields a relatively high tran-
sit probability equivalent to that of a hot Jupiter
(see Section 6). Thus a primary motivation for
follow-up observations is the possible detection of a
planetary transit for a long-period eccentric planet
(Kane & von Braun 2008). A previous example of such a
system can be seen in the case of HD 80606b (Naef et al.
2001), where the secondary eclipse of the 0.93 eccen-
tricity planet was detected by Laughlin et al. (2009)
and later confirmed to also exhibit a primary tran-
sit (Fossey et al. 2009; Garcia-Melendo & McCullough
2009; Moutou et al. 2009). An additional motivation for
obtaining high-precision photometry during the transit
window and periastron passage for HD 20782b is the pos-
sibility of detecting reflected light from the planet since
the small star–planet separation will greatly increase the
amplitude of the phase signature (Kane & Gelino 2010).
Such a detection would allow an estimate of the geomet-
ric albedo of the planet and place constraints upon the at-
mospheric properties and the atmosphere’s radiative and
advective time scales (Seager et al. 2005; Fortney et al.
2008). Note that since the orbital period is 18 months,
an observing opportunity for a particular point in the
orbit will only arise every 3 years since the star will be
largely inaccessible to ground-based observers for each
alternate orbit.
3. STELLAR PROPERTIES
A critical step in quantifying the properties of the
planet lies in understanding the host star. Here we pro-
vide new fundamental parameters and abundances for
HD 20782.
3. The Most Eccentric Exoplanet Known 3
TABLE 1
Stellar Parameters
Parameter Value
V 7.4
B − V 0.63
Distance (pc) 35.5 ± 0.8
Teff (K) 5798 ± 44
log g 4.36 ± 0.06
v sin i (km s−1) 1.7 ± 0.5
[Fe/H] (dex) 0.01 ± 0.03
M⋆ (M⊙) 1.02 ± 0.02
R⋆ (R⊙) 1.09 ± 0.04
Age (Gyrs) 5.53 ± 1.43
3.1. Fundamental Parameters
We acquired a high S/N (300 second integration) spec-
trum of HD 20782 on the night of July 6th, 2014. The
data were acquired using CHIRON, a fiber-fed Echelle
spectrometer (Tokovinin et al. 2013; Brewer et al. 2014),
installed at the 1.5m telescope at Cerro Tololo Inter-
American Observatory (CTIO). CHIRON operates at a
fixed wavelength range of 415–880 nm and a resolution of
R = 79, 000. The spectrum was modeled using the Spec-
troscopy Made Easy (SME) package, described in more
detail by Valenti & Piskunov (1996); Valenti & Fischer
(2005). SME uses an iterative technique that com-
bines model atmosphere analysis with Yonsei-Yale model
isochrones (Demarque et al. 2004) that utilize Hipparcos
photometry and distances (van Leeuwen 2007a,b). This
approach produces a self-consistent convergence with the
measured surface gravity (Valenti et al. 2009).
The results of this analysis are shown in Table 1, in-
cluding values for the surface gravity log g, rotational
velocity v sin i, atmospheric abundance [Fe/H], effective
temperature Teff and stellar isochrone solution (mass M⋆,
radius R⋆, and age). These parameters are consistent
with previous estimates of the stellar properties, such as
those calculated by Takeda et al. (2007). The revised
parameters demonstrate that HD 20782 is quite simi-
lar to the Sun, with the mass and radius being crucial
properties for the subsequent analysis of the planetary
companion in this paper.
3.2. Abundances
Both components of the wide binary system, namely
HD 20781 and HD 20782, have had their elemental abun-
dances measured by a number of different authors. How-
ever, due to the difference in size and spectral type, the
abundances within HD 20782 are easier to determine.
While half as many groups have measured HD 20781 than
HD 20782, there does remain some overlap by some, such
as Neves et al. (2009), Delgado Mena et al. (2010), and
Mack et al. (2014) who did a more in-depth comparison
of the two stars.
Per the analysis in the Hypatia Catalog (Hinkel et al.
2014), the individual abundances within both stars were
renormalized to the Lodders et al. (2009) solar scale.
The largest measurement discrepancy between datasets,
known as the spread, was used to better quantify the
uniformity, or lack thereof, between measurements. This
technique was implemented in the Hypatia Catalog to
better understand the variation in abundances seen when
employing different reduction techniques, due to in-
stances where the spread between groups was larger than
associated error. For the cases where variations between
groups were small, the median value was used as the ul-
timate abundance measurement.
The overall median [Fe/H] content in HD 20781 was 0.1
dex, as compared to 0.15 dex within HD 20782, where
the spread was 0.03 dex and 0.17 dex, respectively. In
other words, the groups that measured HD 20781, while
fewer in number, were in closer agreement regarding the
iron abundance than those that measured HD 20782.
The [Fe/H] determinations for both stars are disparate
compared to the abundances determined by Mack et al.
(2014), which are not part of the Hypatia Catalog, who
measured 0.04±0.03 and -0.02±0.02, respectively. These
are consistent with our new [Fe/H] determination shown
in Table 1.
A wide variety of α-elements (carbon, magnesium,
silicon, and titanium), odd-Z elements (sodium, alu-
minum, and scandium), and iron-peak elements (vana-
dium, chromium, cobalt, and nickel) have been measured
for both stars. For all elements except for [Na/Fe], the
abundance measurements for HD 20781 and HD 20782
were found to be consistent to within error and markedly
sub-solar, or ∼ -0.1 dex. The [Na/Fe] content in
HD 20782 was found to be ∼ 2.5 more than in the com-
panion HD 20781, where [Na/Fe] = -0.09±0.06 dex and
-0.22±0.04 dex, respectively.
4. THE KEPLERIAN ORBIT OF THE PLANET
The highly eccentric planet orbiting HD 20782 was
first reported in Jones et al. (2006) and updated in
O’Toole et al. (2009). We now present a further
six years of radial velocity data from the Anglo-
Australian Planet Search (AAPS). The AAPS is one
of the world’s longest-running planet searches, with
more than 40 planet discoveries in its 16 years of
operation (e.g. Butler et al. 2001; Jones et al. 2010;
Vogt et al. 2010; Wittenmyer et al. 2012; Tinney et al.
2011; Wittenmyer et al. 2014). HD 20782 has been ob-
served on 52 epochs from 1998 Aug 9 to 2013 Sep 19
(Table 2). Precision Doppler measurements are obtained
with the UCLES echelle spectrograph (Diego et al. 1990)
at the 3.9 m Anglo-Australian Telescope (AAT). A 1-
arcsecond slit delivers a resolving power of R ∼45,000.
Calibration of the spectrograph point-spread function is
achieved using an iodine absorption cell temperature-
controlled at 60.0±0.1o
C. The iodine cell superimposes
a forest of narrow absorption lines from 5000 to 6200 ˚A,
allowing simultaneous calibration of instrumental drifts
as well as a precise wavelength reference (Valenti et al.
1995; Butler et al. 1996). The result is a precise ra-
dial velocity shift measured relative to the epoch of
the iodine-free “template” spectrum. AAT velocities for
HD 20782 span a total of 15 years and have a mean in-
ternal uncertainty of 2.4 m s−1
.
Orbital fits to the AAT data allowed predictions of the
next periastron passage of the planet, estimated to be
15 January 2015. We were able to observe HD 20782
during that passage using the Physical Research Lab-
oratory (PRL) optical fiber-fed high-resolution cross-
dispersed echelle spectrograph (PARAS) with the Mount
Abu 1.2 m telescope in India. The PARAS spectro-
graph is temperature-controlled at 25.55±0.01o
C in an
enclosure that is pressure-controlled at 0.10±0.03 mbar.
PARAS has a resolution of R ∼67,000 and obtains RV
4. 4 Stephen R. Kane et al.
TABLE 2
HD 20782 AAT Radial Velocities
Date RV σ
(BJD – 2440000) (m s−1) (m s−1)
11035.31946 21.90 2.33
11236.93065 -6.51 3.27
11527.01731 7.32 3.39
11630.88241 29.70 2.72
11768.30885 -6.64 2.62
11828.11066 -7.64 3.00
11829.27449 -6.64 3.82
11856.13530 -10.37 3.55
11919.00660 -3.62 2.92
11919.99630 -1.67 2.85
11983.89009 4.16 3.32
12092.30437 17.84 2.35
12127.26814 17.70 2.79
12152.16308 23.15 2.50
12187.15965 22.78 2.53
12511.20636 -1.26 2.29
12592.04809 17.40 2.30
12654.96031 15.38 2.34
12859.30551 -202.48 1.90
12946.13833 -18.15 2.08
12947.12246 -14.27 1.77
13004.00143 -0.29 1.85
13044.02367 0.76 2.25
13045.96088 -0.40 1.93
13217.28800 9.01 1.71
13282.22023 20.57 1.87
13398.96924 22.14 1.39
13403.96059 30.40 2.56
13576.30688 -9.14 1.60
13632.28114 -7.62 1.59
13665.18659 6.38 1.72
14013.21622 31.23 1.55
14040.13171 22.12 1.96
14153.97010 -11.56 2.10
14375.24693 13.32 1.70
14544.89158 10.26 2.15
14776.10092 -7.55 1.85
14843.02077 0.09 1.56
14899.92440 -0.65 2.07
15107.24701 16.54 2.78
15170.05453 17.31 2.37
15204.97966 29.22 1.88
15253.91188 -78.17 2.35
15399.32249 -8.19 1.88
15426.31459 -6.89 1.71
15461.23900 -14.81 2.99
15519.13309 8.36 2.00
15844.13584 -145.90 6.54
15845.17956 -185.60 2.28
15846.13671 -156.28 2.32
15964.93095 7.77 2.87
16499.33740 -11.25 3.03
data at a spectral range of 3800 to 6900 ˚Awith simultane-
ous wavelength calibration with a thorium-argon (ThAr)
hollow cathode lamp. The uncertainties for the PARAS
measurements were derived based on the photon noise
estimation procedure explained by Bouchy et al. (2001).
Further details of the PARAS instrument and the data
reduction are described by Chakraborty et al. (2014).
PARAS observations were made under high air mass con-
ditions (1.7–1.9) with no Atmospheric Dispersion Correc-
tor (ADC). The five PARAS observations (see Table 3)
complete our RV dataset and bring the total number of
observations to 57.
The RV data shown in Tables 2 and 3 were used to pro-
duce a revised Keplerian orbital solution. This was per-
formed using the RVLIN package; a partially linearized,
least-squares fitting procedure (Wright & Howard 2009).
TABLE 3
HD 20782 PARAS Radial Velocities
Date RV σ
(BJD – 2440000) (m s−1) (m s−1)
57036.16183 272.25 4.12
57038.14436 127.25 4.09
57039.13336 61.53 3.65
57040.15494 149.14 3.86
57042.12356 183.06 2.98
The uncertainties for the orbital and associated physi-
cal parameters were estimated using the BOOTTRAN
bootstrapping routines described in Wang et al. (2012).
To be sure that known instabilities of the Levenberg-
Marquardt-based RVLIN algorithm did not prevent con-
vergence at these high eccentricities, we reduced the
number of nonlinear parameters in the problem by fix-
ing the eccentricity at 100 values evenly spaced between
0.93 and 0.995 and selecting the value that produced the
minimum χ2
fit.
A fit to the AAT and PARAS data with their instru-
mental uncertainties was unsatisfactory. The rms resid-
uals to the PARAS data are 17 m s−1
, with two excur-
sions at and after RV minimum of over 20 m s−1
, incon-
sistent with typical instrumental uncertainties of under
6 m s−1
. Further, the scatter about the fit to the AAT
data is 6.1 m s−1
, including three excursions larger than
15 m s−1
(up to 17 m s−1
), both significantly larger than
the quoted errors of 2.3 m s−1
. Given that there are only
52 AAT points, we do not expect to see 3 points (∼5%)
with deviations of 15 m s−1
from Gaussian noise unless
the errors are more like 6 m s−1
.
Some component of the scatter about the best fit is
due to intrinsic stellar variability, and some is due to
the precision of the measurements (due to both instru-
mental/algorithmic imprecision and photon noise). The
stellar noise should be the same for both instruments,
meaning that the large excursions seen in the PARAS
data indicate a problem with either the fit or the PARAS
data.
Close examination of points near periastron reveal that
the problem must lie with the instrumental uncertainties,
not the fit. PARAS and AAT have two measurements
(each) at very similar phases (the expected change in RV
between the points in each pair is < 10 m s−1
). However,
in both cases the difference in velocities is over 20 m s−1
,
and in different directions. The combined measurement
uncertainties of the two instruments therefore must be of
order 20 m s−1
.
We attempted a second fit, but inflated both instru-
mental uncertainties by adding, in quadrature, 5 m s−1
and 19 m s−1
to the AAT and PARAS velocities, re-
spectively. These inflations reflect a common stellar jit-
ter component (likely to be around 5 m s−1
) and an
additional, instrument-dependent component added in
quadrature. This resulted in a much more satisfactory
fit: the residuals to the best fit for the two telescopes
have standard deviations of 5.75 m s−1
and 19.85 m s−1
,
respectively, and χ2
values of 1.03 and 1.01, respectively.
There is still a significant outlier to the AAT fit (at
15 m s−1
), but at 2.5σ (using the inflated measurement
uncertainties) this is not unexpected from 52 data points.
5. The Most Eccentric Exoplanet Known 5
TABLE 4
Keplerian Orbital Model
Parameter Value (AAT) Value (AAT+PARAS)
HD 20782 b
P (days) 597.099 ± 0.049 597.065 ± 0.043
Tc
a (BJD – 2,440,000) 17037.788 ± 0.145 17037.794 ± 0.100
Tp
b (BJD – 2,440,000) 17038.510 ± 0.108 17038.458 ± 0.094
e 0.953 ± 0.005 0.956 ± 0.004
ω (deg) 142.2 ± 2.2 142.1 ± 2.1
K (m s−1) 114.9 ± 4.4 116.0 ± 4.2
Mp sin i (MJ ) 1.46 ± 0.03 1.43 ± 0.03
a (AU) 1.397 ± 0.009 1.397 ± 0.009
System Properties
γ (m s−1) 1.95 ± 0.82 1.79 ± 0.80
Measurements and Model
Nobs 52 57
rms (m s−1) 5.91 8.06
χ2
red 1.0 1.14
a Time of mid-transit.
b Time of periastron passage.
We conclude that there is significant instrumen-
tal/observational systematic noise in the PARAS data
due to air mass, of order 20 m s−1
. We also examined
the inclusion of a linear RV trend in our model but found
that this does not improve the quality of the fit. The final
orbital solution from the data is shown in Table 4, where
we have included the solution that uses the AAT data
only for comparison. The AAT+PARAS orbital solution
includes an offset between the AAT and PARAS datasets
as a free parameter, found to be 276.5 ± 8.7 m s−1
. The
γ parameter shown in Table 4 is the systemic velocity of
the system with respect to the zero point of the extracted
RVs (relative to the template spectrum). Thus, there is
an offset between the γ value reported in Table 4 and
the true systemic velocity, reported by Valenti & Fischer
(2005) to be 40.7 km s−1
. Our final AAT+PARAS or-
bital solution is depicted in Figure 2. The bottom panel
of Figure 2 shows the quality of the combined data cov-
erage during periastron passage for this highly eccentric
planet, particularly the additional coverage provided by
the PARAS data.
We note that the transit time we calculate is sensitive
to the weights assigned to the PARAS and AAT data.
The PARAS data favor a transit time that is 0.2–0.3 days
later than the AAT data. Because we do not fully under-
stand the source of the very large scatter in the PARAS
data, we should not assume that our errors are Gaus-
sian. Fortunately, BOOTTRAN uses bootstrapping to
determine its parameter uncertainties, which is appro-
priate for non-normally distributed residuals (although
the underlying fitter minimizes χ2
, and so does assume
Gaussian errors).
5. ASTROMETRIC CONSTRAINTS ON THE ORBIT
To constrain the inclination of the system and possi-
bly refine the estimate of the companion mass, we com-
bine Hipparcos astrometry of HD 20782 with the orbital
parameters obtained from the radial velocity observa-
tions. We use the new reduction of the Hipparcos data
(van Leeuwen 2007a), which presents a significant im-
provement in the overall reliability of astrometric infor-
mation (van Leeuwen 2007b) and includes the Interme-
diate Astrometric Data (IAD) product in a format that
facilitates the quest for signatures of orbital motion. Fol-
lowing the method prescribed by Sahlmann et al. (2011),
we use the spectroscopic elements derived from our RV
solution (Table 4) to search for an orbital signature.
The 5 standard astrometric parameters for the Hip-
parcos solution of a HD20782 can be obtained from the
VizieR Catalogue (van Leeuwen 2007a); these are right
ascension (RA, α=50.01◦
), declination (dec, δ=-28.85◦
),
proper motion in RA (µα=349.33 mas/yr) and dec (µδ=-
65.92 mas/yr), and parallax (̟=28.15 mas). The 5 spec-
troscopic parameters required from the radial velocity
analysis are period (P), eccentricity (e), semi-amplitude
(K), time of periastron (T0), and argument of periastron
(ω). Each Hipparcos observation is reconstructed from
the IAD and fit with a comprehensive model based on
12 parameters: the 5 standard astrometric parameters,
the 5 spectroscopically derived parameters, the inclina-
tion (i), and the longitude of the ascending node (Ω).
In practice, the spectroscopic parameters are treated as
constants since they are considered reliable, and we work
with 7 free parameters. The details of the procedure are
carefully described by Sahlmann et al. (2011), and we
follow their methods to calculate inclination, a new or-
bit, and the significance of the orbit via the permutation
test.
We begin by constructing a two-dimensional i−Ω grid,
where we solve for the remaining five parameters of the
7-parameter model, and the corresponding χ2
. The pa-
rameter values identified by the minimum χ2
value are
used as the starting point for an AMOEBA minimiza-
tion, using the downhill simplex method, to supersede
the limitations imposed by the resolution of the i − Ω
grid. We then perform 100,000 Monte Carlo simulations,
where we generate 1,000 sets of Hipparcos measurements
from the existing data. For each set of Hipparcos abscis-
sae, we execute 100 random draws from the spectroscopic
parameters, in order to inculcate their uncertainties into
our result. Each spectroscopic parameter is assumed to
be a gaussian distribution, with the RV solution and its
errors serving as the mean and standard deviation re-
spectively. The Monte Carlo models are then solved as
6. 6 Stephen R. Kane et al.
2000 2005 2010 2015
Date (year)
−300
−250
−200
−150
−100
−50
0
50
RadialVelocity(m/s)
Mt. Abu/PARAS
AAT/UCLES
−0.4 −0.2 0.0 0.2 0.4
Phase
−250
−200
−150
−100
−50
0
50
RadialVelocity(m/s)
Mt. Abu/PARAS
AAT/UCLES
0.985 0.990 0.995 0.000 0.005
Phase
−250
−200
−150
−100
−50
0
50
RadialVelocity(m/s)
AAT/UCLES
Mt. Abu/PARAS
Fig. 2.— Top: All 57 RV measurements from AAT/PARAS ob-
servations of HD 20782 (see Tables 2 and 3) along with the best-fit
orbital solution (Table 4). RV offsets between datasets have been
accounted for in this figure. Middle: The RV data phased on the
orbital the solution from Table 4, where phase zero corresponds
to superior conjunction. Bottom: A zoomed version of the phased
middle plot which shows the coverage during periastron passage.
described above, to produce 100,000 sets of solution pa-
rameters. The final parameters are defined as the me-
dian of the associated distribution, while the errors are
the interval between the 15.85 percentile and the 84.15
percentile, encompassing 68.3% of the values around the
median.
For completeness, we report here our full set of final pa-
rameters, as offsets to the Hipparcos values. The changes
in right ascension, declination, parallax, proper motion
in RA and declination, and the argument of periastron
0 2 4 6 8 10
a (mas)
0
50
100
150
200
Numberofpseudo−orbits
Fig. 3.— Histogram of the semi-major axes for 1000 randomly
permuted pseudo-orbits of HD 20782. The pseudo-orbits are used
to calculate the significance of the new orbit via the permutation
test, as described by Sahlmann et al. (2011). The solid black line
shows the actual best-fit solution and the dashed line represents the
median Hipparcos single-measurement precision for this system.
are: ∆α = 0.3+1.4
−1.2 mas, ∆δ = 1.0+1.3
−1.1 mas, ∆̟ = 0.2+0.7
−0.7
mas, ∆µα⋆ = 0.0+0.4
−0.4 mas/yr, ∆µδ = 0.1+0.6
−0.6 mas/yr.
We find an inclination of 2.7+2.3
−1.2
◦
and an argument of
periastron 202.5+59.3
−66.3
◦
, but the solution is very poorly
constrained.
The astrometric data covers approximately two orbits
for this system, so phase coverage should not inhibit the
recovery of any significant orbital signatures. Unfortu-
nately, the projected minimum semi-major axis of our
new solution is very small (a sin i = 0.05 mas) compared
to the median Hipparcos single-measurement precision
for this target (3.5 mas), as shown in Figures 3 and 4.
We perform a permutation test to verify the significance
of our result by comparing the semimajor axis of the new
solution orbit with 1,000 pseudo orbits generated from
random permutations of the astrometric data, similar to
Sahlmann et al. (2011). Figure 3 illustrates the calcula-
tion of a low significance orbit (68.2%, which is almost
exactly at the 1σ level of detection), confirming that the
Hipparcos data contains little or no orbital signature.
The new Hipparcos reduction has this target flagged as
having a good fit with just the 5 astrometric parame-
ters, which is consistent with the fact that adding the
7 RV parameters does not seem to change the solution.
Sahlmann et al. (2011) emphasize that orbital solutions
at this significance level are prone to very large biases,
and the calculated values and their errors should be con-
sidered highly suspect. We present our full set of orbital
parameters here only to facilitate future comparison of
analytical methods, and not for direct application.
On the other hand, simulations by Sahlmann et al.
(2011) show that orbits are always detected at the 3σ
level when the semi-major axis is at least 70% of the Hip-
parcos precision on a target. Any orbital signature above
2.45 mas would have been detectable in this Hipparcos
dataset, and this helps to set an upper limit on the com-
panion mass. Using this assertion, we get a lower limit on
inclination (1.22◦
) and an upper limit on the companion
mass (66 MJ ). Although the consideration of astromet-
ric data does not allow us to put tight constraints on the
inclination of the system, the non-detection of an orbit
7. The Most Eccentric Exoplanet Known 7
10 5 0 −5 −10
−10
−5
0
5
10
10 5 0 −5 −10
∆ α* (mas)
−10
−5
0
5
10
∆δ(mas)
Fig. 4.— The red line shows the orbital signature detected in the
Hipparcos data when combined with orbital parameters from the
radial velocity solution. As projected on sky, North is up and East
is left. Open circles mark the individual Hipparcos measurements.
Dashed lines with orientation along the scan angle ψ and length
given by the residual of the orbital solution connect the measure-
ments with the predicted location from our model. This illustrates
the difficulty of detecting an orbit with such a small projected
semi-major axis, given the median Hipparcos single-measurement
precision on this target.
Fig. 5.— The projected (AU) and angular (′′) separation of
HD 20782b from the host star as a function of orbital phase, where
phase zero corresponds to superior conjunction.
allows us to rule out a stellar binary system. Verification
of this could be achieved through high-contrast adaptive-
optics imaging of the system at predicted apastron pas-
sage. Figure 5 shows the projected and angular separa-
tion of the planet and star for one complete face-on orbit,
where phase zero corresponds to superior conjuction as
described by Kane (2013). An additional consequence of
our astrometric constraint is that the transit probability
is increased by a small amount since inclinations below
1.22 degrees are ruled out.
6. PLANETARY TRANSIT PROSPECTS
As described in Section 2, one of the most interest-
ing aspects of HD 20782b is the relatively large tran-
sit probability compared with the orbital period. The
transit probability is a function of the stellar and plane-
tary radii and the star–planet separation along the line
of sight (Kane & von Braun 2008). For HD 20782, we
use the stellar radius shown in Table 1 and adopt a plan-
etary radius of Rp = 1.0 RJ given the minimum mass
of 1.41 MJ (see Table 4) and using the mass-radius rela-
tionship described by Kane & Gelino (2012a).
If the planet were in a circular orbit with the same
semi-major axis, the transit probability would be 0.4%.
The extreme eccentricity of the orbit results in star–
planet separation of 0.061 AU at periastron and 0.076 AU
at inferior conjunction where a transit is possible. Such
a separation is similar to that of a hot Jupiter in a circu-
lar orbit. Inferior conjunction occurs when ω + f = 90◦
;
in this case, the true anomaly is f = 307.9◦
at the time
of mid-transit. This orbital orientation results in an en-
hanced transit probability of 7.1%.
A further influence of the high eccentricity on the tran-
sit parameters is the expected transit duration. Since
the separation at inferior conjunction is comparable to a
hot Jupiter, the duration is likewise reduced and has an
amplitude of 0.13 days (3.1 hours) for a central transit.
The epoch of mid-transit shown in Table 4 was calculated
using the same Monte-Carlo bootstrap method used to
calculate the orbital parameter uncertainties. The time
of mid-transit corresponds to a calendar date of 15 Jan-
uary 2015 and a UT of 7:02. The uncertainty on this
time is 0.1 days which results in a total 1σ transit win-
dow of 0.33 days (7.6 hours). The estimated depth of
the transit is 0.96% and so should be readily observable
in typical millimag photometry. However, the infrequent
occurrence of such events (see Section 2) motivated ob-
servations from both ground and space.
7. PHOTOMETRIC OBSERVATIONS
The derived physical and orbital properties of
HD 20782b described in previous sections motivated pho-
tometric monitoring of the host star for stellar variability
and planetary transit/phase signatures. Here we describe
our photometric observations and results in detail.
7.1. APT Photometry
We collected a total of 191 nightly photometric ob-
servations of HD 20782 during its 2013–14, 2014–15, and
2015–16 observing seasons to search for stellar variability.
The observations were acquired with the T8 0.80 m auto-
matic photoelectric telescope (APT), one of several au-
tomated telescopes operated by Tennessee State Univer-
sity (TSU) located at Fairborn Observatory in southern
Arizona. The T8 APT is equipped with a two-channel
precision photometer that uses a dichroic filter and two
EMI 9124QB bi-alkali photomultiplier tubes to measure
the Str¨omgren b and y pass bands simultaneously. We
computed the differential magnitudes of HD 20782 with
respect to the mean brightness of its three constant com-
parison stars. To improve the precision further, we com-
bined the differential b and y observations into a sin-
gle (b + y)/2 “passband.” The TSU APTs, their preci-
sion photometers, observing strategy, and data reduction
techniques are described in detail by Henry (1999). A
summary of the photometric data for HD 20782 is given
in Table 5.
The nightly observations of HD 20782 are plotted in
the top panel of Figure 6 in our (b + y)/2 passband. The
8. 8 Stephen R. Kane et al.
TABLE 5
Summary of photometric observations for HD 20782
Observing Julian Date Range Mean Sigma
Season Nobs (HJD – 2,400,000) (mag) (mag)
2013–14 43 56622–56701 1.01241 0.00183
2014–15 89 56943–57045 1.01206 0.00228
2015–16 59 57293–57390 1.01128 0.00171
Fig. 6.— HD 20782 APT photometry acquired during three con-
secutive observing seasons. Top: The relative photmetry as a func-
tion of Heliocentric Julian Date. Middle: The power spectra from
a fourier analysis of all seasons photometry. Bottom: Sinusoidal
fit to the most significant period found from the fourier analysis.
Our analysis described in the text demonstrates that this period is
spurious.
observing seasons are quite short from Fairborn Obser-
vatory, only three months in length, because of the star’s
southerly declination of −29◦
. The observations scat-
ter about their grand mean (indicated by the horizontal
dotted line) with a standard deviation of 0.00205 mag, as
given in the upper right corner of the top panel. This is
essentially the limit of precision for the HD 20782 obser-
vations because the star’s southerly declination results in
all measurements being made at air mass values between
2.0 and 2.4 (see Henry (1999), Figure 8).
The middle and bottom panels of Figure 6 show the
frequency spectrum of the data set and the phase curve
computed with the best frequency, respectively. Our fre-
quency analysis is based on least-squares sine fits with
trial frequencies between 0.01 and 0.95 c/d, correspond-
ing to periods between one and 100 days. The good-
ness of fit at each frequency is measured as the reduc-
tion factor in the variance of the original data, whose
value lies between the extremes of 0.0 and 1.0. A re-
duction factor of 0.0 corresponds to the case where the
variance in the residuals from a least-squares sine fit to
the observational data at some trial frequency have the
same value as the variance in the original data, i.e., no
reduction in the variance takes place at that particular
frequency. A reduction factor of 1.0 corresponds to the
extreme case where the variance in the residuals of the
sine fit is 0.0, i.e., the sine curve fits the data perfectly
with no residuals. The frequency spectrum in the mid-
dle panel shows several peaks with reduction factors near
0.1, but no peak stands out above the others to suggest a
stellar rotation period. We ran simulations adding com-
puted sine curves to our data sets and found that coher-
ent variations with peak-to-peak amplitudes of ∼ 0.004
mag or larger would be detectable in our light curves.
This places an upper limit to any periodic modulation
for HD 20782, such as rotational modulation caused by
starspots. This is consistent with the low level of mag-
netic activity (logR’HK = -4.91) given in the discovery
paper of Jones et al. (2006) and demonstrates that our
best-fit period of 1.2619 days in the bottom panel is spu-
rious. In addition to the absense of rotational modula-
tion, we find no evidence for longer-term variability; the
three seasonal means in Table 5 scatter about their grand
mean with a standard deviation of only 0.00058 mag.
7.2. MOST Observations and Transit Window
Given the size of the transit windows and the relatively
infrequent opportunities to observe them (see Sections 2
and 6), we elected to make use of the Microvariability
and Oscillations of STars (MOST) satellite to observe
HD 20782 during the next scheduled transit window.
MOST has an aperture of 15 cm and a filter passband
covering the range 375–675 nm, making it well suited to
obtain precision optical photometry of very bright stars
(Walker et al. 2003; Matthews et al. 2004).
Observations of HD 20782 commenced at HJD
2457035.3 (2015 January 12 19:11 UT) and concluded
7 days later at HJD 2457042.3 (2015 January 19 19:11
UT). The predicted time of mid-transit (see Table 4)
was BJD 2457037.794 (2015 January 15 07:02 UT). The
star is outside of MOST’s Continuous Viewing Zone and
so required observations outside of normal operational
parameters. For each 101 min orbit, MOST was able to
acquire the target field for 20 mins. Exposure times were
0.6 secs to allow for both the brightness of the target and
scattered light due to the roll angle of the spacecraft with
respect to the Sun. This resulted in photometry with a
1σ RMS precision of 0.07%.
During the week of MOST observations, a total of 257
measurements of HD 20782 were acquired. The resulting
relative photometry of the data are shown in Figure 7,
along with a solid line that indicates the predicted lo-
cation and depth of a possible transit. The 1σ transit
window (0.33 days) was described in Section 6. We use
the 3σ transit window (0.43 days) to draw vertical dashed
lines in Figure 7. A central transit of the planet (impact
parameter of b = 0) is ruled out for most locations within
the transit window. The cadence of the observations is
such that a transit duration half that of a central transit
could have been missed within the 1σ transit window.
Such a duration corresponds to an impact parameter of
b = 0.87, above which transits cannot be ruled out by
9. The Most Eccentric Exoplanet Known 9
Fig. 7.— MOST photometry of HD 20782 acquired for ∼7 days surrounding the predicted transit mid-point. The solid line indicates the
location and depth of a possible transit and the vertical dashed lines are the boundaries of the 3σ transit window.
our photometry.
A further consideration is the detection of the Rossiter-
McLaughlin (R-M) effect during a possible transit. The
amplitude of the R-M effect is shown by (Gaudi & Winn
2007) to be
KR = v sin i
(Rp/R⋆)2
1 − (Rp/R⋆)2
(1)
Using our stellar parameters from Table 1 and the tran-
sit parameters described in Section 6, the amplitude of
the R-M effect for a transit of HD 20782b is predicted to
be ∼15.5 m s−1
. Two of our RV measurements (one each
from AAT and PARAS) are within the transit window,
shown close to 0.5 phase in the bottom panel of Figure 2.
Neither of these measurements show evidence of any sig-
nificant deviation from our Keplerian model. Thus the
RV data are consistent with the MOST photometry lead-
ing to the conclusion that the planet does not transit the
host star.
7.3. Evidence of Phase Variations
The phase variations of a planet as it orbits the host
star has become a detectable signature in the era of high-
precision photometry. Numerous examples of phase sig-
natures have been detected from the planets detected
with the Kepler mission (Esteves et al. 2013, 2015).
Exoplanets that are close to their host stars have gen-
erally been found to have low geometric albedos, such
as the low geometric albedo of HAT-P-7b (Welsh et al.
2010) and the null detection of phase variations from
HD 209458b (Rowe et al. 2008). There are exceptions
to the rule, however, such as the case of Kepler-7b
(Demory et al. 2011), and it is likely that a greater un-
derstanding of atmospheric processes is needed to explain
this diversity (Demory 2014). Kane & Gelino (2010) de-
veloped a geometric albedo model that scales the geomet-
ric albedo with star–planet separation. The implication
of the model for planets in eccentric orbits is that the
geometric albedo is time dependent, with an assumption
that reflective/scattering condensates in the upper at-
mosphere are removed during periastron passage by the
increase in radiative flux from the host star. The gener-
alized expression for the planet to host flux ratio is given
by
ǫ(α, λ) ≡
fp(α, λ)
f⋆(λ)
= Ag(λ)g(α, λ)
R2
p
r2
(2)
where α is the phase angle, Ag is the geometric albedo,
g is the phase function, Rp is the planetary radius, and
r is the star–planet separation. This separation is given
by
r =
a(1 − e2
)
1 + e cosf
(3)
where f is the true anomaly. The phase angle, α, is
defined to be zero at superior conjunction. A model
of geometric albedo time-dependence assumes that the
planetary atmosphere responds to the change in incident
flux on timescales comparable to the duration of the pe-
riastron encounter. This effect has been modeled for
the eccentric planet HAT-P-2b at infrared wavelengths
by Lewis et al. (2013). Thus Kane & Gelino (2010) pre-
dicted that, although the largest phase variations of ec-
centric planets occur during a relatively short fraction of
their orbital phase, the amplitude of the signature would
be lowered by the subsequent darkening of their atmo-
spheres during periastron.
For HD 20782b, we calculated the predicted phase
variations of the planet with respect to the inferior
conjunction (transit) and periastron times, shown as a
dashed line in the top panel of Figure 8. These or-
bital locations are very close to each other (see Fig-
ure 1), separated by only 0.66 days. The location
of superior conjunction where α = 0 occurs 5.63
days after the periastron passage. All three of these
orbital locations are covered by the MOST observa-
tions described in Section 7.2. We include the ad-
ditional effects of ellipsoidal variations (Drake 2003;
Zucker et al. 2007; Kane & Gelino 2012b) and Doppler
boosting (Loeb & Gaudi 2003; Faigler & Mazeh 2011) in
10. 10 Stephen R. Kane et al.
Fig. 8.— Top: The predicted flux variations of the HD 20782 system due to reflected light from the planet (dashed line), ellipsoidal
variations (dotted line), and Doppler boosting (dot-dashed line). The sum of these three effects is shown as a solid line. This assumes a
time-varying geometric albedo, as formulated by Kane & Gelino (2010). The zoomed panel shows the maximum phase variation along with
the orbital phase location of periastron and the predicted transit time described in Section 6. Middle: The MOST data with the running
average shown as a solid line. Bottom: The binned MOST data along with a model of the phase variations.
11. The Most Eccentric Exoplanet Known 11
the top panel of Figure 8, shown as dotted and dot-
dashed lines respectively. The combined effect of all three
(phase variations, ellipsoidal variations, and Doppler
boosting) is shown as a solid line. For the ellipsoidal
component, we have assumed a gravity darkening expo-
nent of β = 0.32 (Lucy 1967). For the Doppler boosting
coefficient, we calculate a value of αbeam = −1.21 using
the stellar temperature from Table 1 and the method-
ology of Loeb & Gaudi (2003). Using the model of a
distance-dependent geometric albedo and Hilton phase
function (Kane & Gelino 2010), we determined that the
amplitude of the phase variations is comparable to the
Doppler boosting, whereas the ellipsoidal component is a
minor contribution to the total flux variations. Another
point worth noting is that this model assumes an orbit
that is close to edge-on. The effect of orbital inclina-
tion on the relative amplitudes of the three contributing
components is minor except for orbits close to face-on
(Kane & Gelino 2011a).
As described in Section 7.2, the original intent of ac-
quiring the MOST data was for the purpose of observ-
ing a potential transit event. Evidence of phase varia-
tions was unexpected due to the low predicted ampli-
tude shown in the top panel of Figure 8. To determine
the overall trend in the MOST data, we calculated a run-
ning mean of the data using 20 data points either side
of each measurement to calculate the running mean at
that location. The results of this calculation are shown
as a solid line along with the individual measurements
(including error bars) in the middle panel of Figure 8,
where we have adjusted the vertical scale of the plot to
the range of the running mean values, using the aver-
age of the running mean values as the zero-point. The
apparent brightening of the host star between the trun-
cated dates of 38 and 39 on the plot is where the peak
of the phase variations are predicted to occur. This was
diagnosed from an instrumentation point of view, and it
was determined that the change in the brightness was
not caused by any aspect of the MOST instrumentation
or data reduction issues.
We tested the likelihood whether this could be caused
by an alignment between intrinsic stellar variability and
the expected periastron passage, by conducting a Monte-
Carlo simulation in which we treat the observed data as
representative of possible stellar variability and randomly
rearrange the data to see how often a similar chance
alignment can occur. Each random permutation of the
observed flux values to the times of observation resulted
in a new dataset for which the running mean was cal-
culated and then analyzed for significant peaks in the
flux. The percentage of simulations for which a specific
criteria was met was taken as the probability that the
criteria would have been satisfied by chance. Based on
10,000 realizations of this simulation, the probability of
a peak occurring in the 38–39 date range is ∼17%, and
the probability of that peak being of equal or greater
amplitude than the observed peak is ∼4%. If indeed
the observed peak is related to the close passage of the
planet to the star, the flux variations may indicate that
the assumption by Kane & Gelino (2010) that the pres-
ence of reflective condensates in a planetary atmosphere
changes on timescales comparable with the periastron
passage is likely incorrect for highly eccentric orbits. In
fact, the larger the eccentricity, the more inconsistent
Fig. 9.— The predicted blackbody flux of HD 20782b, assuming
a calculated temperature of ∼1400 K. The passband boundaries of
MOST are indicated by the vertical dashed lines. The blackbody
calculation assumes zero Bond albedo and zero heat redistribution
(hot dayside model) and thus represents a maximum flux scenario.
Of the integrated flux, 0.02% falls within the MOST passband.
the assumption becomes with the radiative and advective
timescales of the atmosphere. Furthermore, the possi-
ble presence of phase variations indicates the companion
is not self-luminous, further supporting the claim that
the companion is planetary rather than stellar in nature
(Kane & Gelino 2012b).
To investigate this further, we binned the MOST pho-
tometry into 15 evenly spaced time intervals. The best-fit
model to the binned data is shown in the bottom panel of
Figure 8 where the model includes ellipsoidal variations
and Doppler boosting as well as phase variations. The
best-fit inclination of the planetary orbit is i = 30◦
. A fit
of the data to both the described model and a constant
model resulted in ∆χ2
= 24 which shows that the phase
model is quantitatively favored. However, the model uses
a companion radius of ∼5 Jupiter radii and a geometric
albedo of unity, which is a physically unlikely scenario.
Thus there is either an additional component missing in
our model of the data, or the data may be insufficient
to fully characterize the flux variations, or some combi-
nation of the two. As noted above, the most compelling
aspects of the variations described here are the timing of
the variations with those predicted by the phase model,
combined with the extreme eccentricity of the planet.
This system is clearly highly unusual amongst the known
exoplanets, and we cannot exclude the possibility of un-
accounted for physics occuring during the extreme con-
ditions of periastron.
A possible missing factor is that of thermal emission.
This has been shown to be a significant component at
the Kepler passband (Demory et al. 2011). The Kepler
passband however is significantly broader than that used
by MOST (see Section 7.2). We calculated this compo-
nent for our observations by estimating the equilibrium
temperature of the planet. To do so, we assumed the
most extreme case of zero heat redistribution (hot day-
side) and zero Bond albedo (Kane & Gelino 2011b). This
produces a peak equilibrium temperature at periastron
of ∼1400 K. The resulting blackbody spectrum is shown
in Figure 9 along with the passband of MOST, depicted
as vertical dashed lines. Of the integrated flux from the
thermal emission, only 0.02% of the total flux falls within
12. 12 Stephen R. Kane et al.
the passband of our observations. This corresponds to a
flux ratio of planet to star thermal emission in the MOST
passband of ∼ 1.5 × 10−6
. We conclude that any phase
variations due to the planet are dominated by the opti-
cal component. Further data with higher precision are
needed to confirm the presence of the variations and con-
strain the reflective properties of this fascinating planet
as it passes through periastron.
8. CONCLUSIONS
Exoplanets in eccentric orbits remain some of the most
intriguing discoveries of recent decades. Although the
semi-amplitude of their RV variations is systematically
higher, the orbits of highly eccentric planets are difficult
to characterize due the rapid variation at periastron pas-
sage. We have refit the orbit of HD 20782b, consistent
with it being the most extreme of these eccentricity cases
and have provided new stellar and planetary parameters.
Our RV measurements acquired during the brief duration
of periastron passage allow a detailed orbital ephemeris
to be constructed, despite the relatively long period of
∼18 months. Our analysis of the Hipparcos astrometry
for HD 20782 constrains the inclination sufficiently such
that the companion is likely to be planetary rather than
stellar. The uncertainties associated with our astromet-
ric analysis leave open the possibility that the companion
lies within the brown dwarf mass regime. It is expected
that further astrometric data from the Gaia mission will
significantly improve these constraints (Perryman et al.
2014). Even with a relatively high transit probability of
∼7%, we have shown that the planet does not transit the
host star.
The possible phase variations soon after periastron
might be induced in part by stellar light reflected off the
planet’s atmosphere. Although our modeling is incom-
plete, if this hypothesis is true then it raises interesting
questions regarding the conditions to which such an ex-
treme orbit exposes the planet. In particular, the effects
of rotation rate and radiative/advective timescales on at-
mospheric dynamics may be overwhelmed by the short
yet intense conditions that occur at the closest approach
of the planet to the star. It has been further noted by
several studies that the brightest region of the planet is
shifted westward of the substellar point, caused by a rel-
atively cloudy western hemisphere (Demory et al. 2011;
Esteves et al. 2015; Hu et al. 2015; Shporer & Hu 2015).
Additionally, it seems likely that, although planets in
short-period orbits tend to have relatively low geomet-
ric albedos, long-period planets in eccentric orbits retain
a high geometric albedo during the periastron passage
since the atmosphere does not have time to respond to
the change in incident flux. The result of this is a higher
than expected flux ratio of the planet to the star at op-
tical wavelengths. Thus, eccentric planets present a par-
ticularly lucrative observing opportunity for the study
of planetary atmospheres, provided one is able to accu-
rately predict when the peak flux variations are expected
to occur.
Further observations of this system at times close to
inferior conjunction are highly encouraged. The next
two times of inferior conjunction predicted from our
ephemeris are BJD 2457634.859 ± 0.123 (2016 Septem-
ber 3 8:36 UT) and BJD 2458231.924±0.153 (2018 April
23 10:10 UT). In each case, the subsequent superior con-
junction occurs ∼6.29 days after the inferior conjunction.
Matching these times to those when the target is most
visible is not trivial and the timescale of the periastron
passage is best suited to continuous space-based observa-
tions. Possibilities for these upcoming windows would be
a perfect use for upcoming missions that are optimized
for bright star observations, such as the CHaracterizing
ExOPLanet Satellite (CHEOPS). A deeper understand-
ing of the orbits and atmospheres of eccentric planets are
key milestones towards unlocking the origin and nature
of these mysterious objects.
ACKNOWLEDGEMENTS
The authors would like to thank the anonymous ref-
eree, whose comments greatly improved the quality of
the paper. S.R.K and N.R.H. acknowledge financial
support from the National Science Foundation through
grant AST-1109662. G.W.H. acknowledges long-term
support from Tennessee State University and the State
of Tennessee through its Centers of Excellence program.
H.R.A.J acknowledges support from STFC via grants
ST/M001008/1 and Leverhulme Trust RPG-2014-281.
The authors thank the Gurushikar, Mt. Abu Obser-
vatory Staff and the PARAS technical staff for the ob-
servations with PARAS. The PARAS program is sup-
ported completely by the Physical Research Laboratory,
Dept. of Space, Govt. of India. The results reported
herein benefited from collaborations and/or information
exchange within NASA’s Nexus for Exoplanet System
Science (NExSS) research coordination network spon-
sored by NASA’s Science Mission Directorate.
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