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Kamen O. Todorov,
Drake Deming, Heather A. Knutson,
Adam Burrows,
Jonathan J. Fortney,
Nikole K. Lewis,
Nicolas B. Cowan,
Eric Agol,
Jean-Michel Desert,
Pedro V. Sada,
David Charbonneau,
Gregory Laughlin,
Jonathan Langton,
Adam P. Showman
[show abstract]
[hide abstract]
ABSTRACT: We present Warm Spitzer/IRAC secondary eclipse time series photometry of
three short-period transiting exoplanets, HAT-P-3b, HAT-P-4b and HAT-P-12b, in
both the available 3.6 and 4.5 micron bands. HAT-P-3b and HAT-P-4b are
Jupiter-mass, objects orbiting an early K and an early G dwarf stars,
respectively. For HAT-P-3b we find eclipse depths of 0.112%+0.015%-0.030% (3.6
micron) and 0.094%+0.016%-0.009% (4.5 micron). The HAT-P-4b values are
0.142%+0.014%-0.016% (3.6 micron) and 0.122%+0.012%-0.014% (4.5micron). The two
planets' photometry is consistent with inefficient heat redistribution from
their day to night sides (and low albedos), but it is inconclusive about
possible temperature inversions in their atmospheres. HAT-P-12b is a
Saturn-mass planet and is one of the coolest planets ever observed during
secondary eclipse, along with hot Neptune GJ 436b and hot Saturn WASP-29b. We
are able to place 3$\sigma$ upper limits on the secondary eclipse depth of
HAT-P-12b in both wavelengths: < 0.042% (3.6 micron) and <0.085% (4.5 micron).
We discuss these results in the context of the {\it Spitzer} secondary eclipse
measurements of GJ 436b and WASP-29b. It is possible that we do not detect the
eclipses of HAT-P-12b due to high eccentricity, but find that weak planetary
emission in these wavelengths is a more likely explanation. We place 3 sigma
upper limits on the |e cos(omega)| quantity (where e is eccentricity and omega
is the argument of periapsis) for HAT-P-3b (<0.0081) and HAT-P-4b (<0.0042),
based on the secondary eclipse timings.
05/2013;
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Nikole K. Lewis, Heather A. Knutson,
Adam P. Showman,
Nicolas B. Cowan,
Gregory Laughlin,
Adam Burrows,
Drake Deming,
Justin R. Crepp,
Kenneth J. Mighell,
Eric Agol, [......],
Debra A. Fischer,
Jonathan J. Fortney,
Joel D. Hartman,
Sasha Hinkley,
Andrew W. Howard,
John Asher Johnson,
Melodie Kao,
Jonathan Langton,
Geoffrey W. Marcy,
Joshua N. Winn
[show abstract]
[hide abstract]
ABSTRACT: We present the first secondary eclipse and phase curve observations for the
highly eccentric hot Jupiter HAT-P-2b in the 3.6, 4.5, 5.8, and 8.0 \mu m bands
of the Spitzer Space Telescope. The 3.6 and 4.5 \mu m data sets span an entire
orbital period of HAT-P-2b, making them the longest continuous phase curve
observations obtained to date and the first full-orbit observations of a planet
with an eccentricity exceeding 0.2. We present an improved non-parametric
method for removing the intrapixel sensitivity variations in Spitzer data at
3.6 and 4.5 \mu m that robustly maps position-dependent flux variations. We
find that the peak in planetary flux occurs at 4.39+/-0.28, 5.84+/-0.39, and
4.68+/-0.37 hours after periapse passage with corresponding maxima in the
planet/star flux ratio of 0.1138%+/-0.0089%, 0.1162%+/-0.0080%, and
0.1888%+/-0.0072% in the 3.6, 4.5, and 8.0 \mu m bands respectively. We compare
our measured secondary eclipse depths to the predictions from a one-dimensional
radiative transfer model, which suggests the possible presence of a transient
day side inversion in HAT-P-2b's atmosphere near periapse. We also derive
improved estimates for the system parameters, including its mass, radius, and
orbital ephemeris. Our simultaneous fit to the transit, secondary eclipse, and
radial velocity data allows us to determine the eccentricity and argument of
periapse of HAT-P-2b's orbit with a greater precision than has been achieved
for any other eccentric extrasolar planet. We also find evidence for a
long-term linear trend in the radial velocity data. This trend suggests the
presence of another substellar companion in the HAT-P-2 system, which could
have caused HAT-P-2b to migrate inward to its present-day orbit via the Kozai
mechanism.
02/2013;
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Drake Deming,
Ashlee Wilkins,
Peter McCullough,
Adam Burrows,
Jonathan J. Fortney,
Eric Agol,
Ian Dobbs-Dixon,
Nikku Madhusudhan,
Nicolas Crouzet,
Jean-Michel Desert, [......],
Korey Haynes, Heather A. Knutson,
Michael Line,
Zazralt Magic,
Avi M. Mandell,
Sukrit Ranjan,
David Charbonneau,
Mark Clampin,
Sara Seager,
Adam P. Showman
[show abstract]
[hide abstract]
ABSTRACT: Exoplanetary transmission spectroscopy in the near-infrared using
Hubble/NICMOS is currently ambiguous because different observational groups
claim different results from the same data, depending on their analysis
methodologies. Spatial scanning with Hubble/WFC3 provides an opportunity to
resolve this ambiguity. We here report WFC3 spectroscopy of the giant planets
HD209458b and XO-1b in transit, using spatial scanning mode for maximum
photon-collecting efficiency. Our new analysis technique achieves nearly
photon-limited precision even at the high flux levels collected in spatial scan
mode. We evaluate our precision using two independent error analyses to measure
possible red noise. Both methods indicate that our errors are within 6% (XO-1)
and 26% (HD209458b) of the photon-limit at a spectral resolving power of 70.
These high flux level data allow us to attain a precision better than 0.01% per
spectral channel. For XO-1b we achieve an average error in transit depth of 96
ppm, and for HD209458b our average error is 36 ppm per spectral channel over
our analyzed range from 1.11-1.65 microns. We detect water absorption in both
planets, but not other molecules. The absorptions we measure are much more
subtle than claimed by some previous observers. Both planets exhibit absorption
of approximately 200 ppm at the water peak near 1.38 microns. Our result for
XO-1b contradicts the much larger absorption derived from NICMOS spectroscopy.
The weak water absorption we measure for HD209458b is reminiscent of the
weakness of sodium absorption in the first transmission spectroscopy of an
exoplanet atmosphere by Charbonneau et al.(2002). Model atmospheres having
uniformly-distributed extra opacity of 0.012 cm^2/g account approximately for
both our water measurement and the sodium absorption in this planet.
02/2013;
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Benjamin J. Fulton,
Andrew W. Howard,
Joshua N. Winn,
Simon Albrecht,
Geoffrey W. Marcy,
Justin R. Crepp,
Gaspar A. Bakos,
John Asher Johnson,
Joel D. Hartman,
Howard Isaacson, Heather A. Knutson,
Ming Zhao
[show abstract]
[hide abstract]
ABSTRACT: We present the measured projected obliquity -- the sky-projected angle
between the stellar spin axis and orbital angular momentum -- of the inner
planet of the HAT-P-17 multi-planet system. We measure the sky-projected
obliquity of the star to be \lambda=19+/-15 degrees by modeling the
Rossiter-McLaughlin (RM) effect in Keck/HIRES radial velocities (RVs). The
anomalous RV time series shows an asymmetry relative to the midtransit time,
ordinarily suggesting a nonzero obliquity -- but in this case at least part of
the asymmetry may be due to the convective blueshift, increasing the
uncertainty in the determination of \lambda. We employ the semi-analytical
approach of Hirano et al. (2011) that includes the effects of macroturbulence,
instrumental broadening, and convective blueshift to accurately model the
anomaly in the net RV caused by the planet eclipsing part of the rotating star.
Obliquity measurements are an important tool for testing theories of planet
formation and migration. To date, the measured obliquities of ~50 Jovian
planets span the full range, from prograde to retrograde, with planets orbiting
cool stars preferentially showing alignment of stellar spins and planetary
orbits. Our results are consistent with this pattern emerging from tidal
interactions in the convective envelopes of cool stars and close-in planets. In
addition, our 1.8 years of new RVs for this system show that the orbit of the
outer planet is more poorly constrained than previously thought, with an
orbital period now in the range of 10-36 years.
01/2013;
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Heather A. Knutson,
Nikole Lewis,
Jonathan J. Fortney,
Adam Burrows,
Adam P. Showman,
Nicolas B. Cowan,
Eric Agol,
Suzanne Aigrain,
David Charbonneau,
Drake Deming,
Jean-Michel Desert,
Gregory W. Henry,
Jonathan Langton,
Gregory Laughlin
[show abstract]
[hide abstract]
ABSTRACT: We present new, full-orbit observations of the infrared phase variations of
the canonical hot Jupiter HD 189733b obtained in the 3.6 and 4.5 micron bands
using the Spitzer Space Telescope. When combined with previous phase curve
observations at 8.0 and 24 micron, these data allow us to characterize the
exoplanet's emission spectrum as a function of planetary longitude. We utilize
improved methods for removing the effects of intrapixel sensitivity variations
and accounting for the presence of time-correlated noise in our data. We
measure a phase curve amplitude of 0.1242% +/- 0.0061% in the 3.6 micron band
and 0.0982% +/- 0.0089% in the 4.5 micron band. We find that the times of
minimum and maximum flux occur several hours earlier than predicted for an
atmosphere in radiative equilibrium, consistent with the eastward advection of
gas by an equatorial super-rotating jet. The locations of the flux minima in
our new data differ from our previous observations at 8 micron, and we present
new evidence indicating that the flux minimum observed in the 8 micron is
likely caused by an over-shooting effect in the 8 micron array. We obtain
improved estimates for HD 189733b's dayside planet-star flux ratio of 0.1466%
+/- 0.0040% at 3.6 micron and 0.1787% +/- 0.0038% at 4.5 micron; these are the
most accurate secondary eclipse depths obtained to date for an extrasolar
planet. We compare our new dayside and nightside spectra for HD 189733b to the
predictions of models from Burrows et al. (2008) and Showman et al. (2009). We
find that HD 189733b's 4.5 micron nightside flux is 3.3 sigma smaller than
predicted by the Showman et al. models, which assume that the chemistry is in
local thermal equilibrium. We conclude that this discrepancy is best-explained
by vertical mixing, which should lead to an excess of CO and correspondingly
enhanced 4.5 micron absorption in this region. [abridged]
06/2012;
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[show abstract]
[hide abstract]
ABSTRACT: We observe two secondary eclipses of the strongly irradiated transiting
planet WASP-33b in the Ks band, and one secondary eclipse each at 3.6- and 4.5
microns using Warm Spitzer. This planet orbits an A5V delta-Scuti star that is
known to exhibit low amplitude non-radial p-mode oscillations at about
0.1-percent semi-amplitude. We detect stellar oscillations in all of our
infrared eclipse data, and also in one night of observations at J-band out of
eclipse. The oscillation amplitude, in all infrared bands except Ks, is about
the same as in the optical. However, the stellar oscillations in Ks band have
about twice the amplitude as seen in the optical, possibly because the
Brackett-gamma line falls in this bandpass. We use our best-fit values for the
eclipse depth, as well as the 0.9 micron eclipse observed by Smith et al., to
explore possible states of the exoplanetary atmosphere, based on the method of
Madhusudhan and Seager. On this basis we find two possible states for the
atmospheric structure of WASP-33b. One possibility is a non-inverted
temperature structure in spite of the strong irradiance, but this model
requires an enhanced carbon abundance (C/O>1). The alternative model has solar
composition, but an inverted temperature structure. Spectroscopy of the planet
at secondary eclipse, using a spectral resolution that can resolve the water
vapor band structure, should be able to break the degeneracy between these very
different possible states of the exoplanetary atmosphere. However, both of
those model atmospheres absorb nearly all of the stellar irradiance with
minimal longitudinal re-distribution of energy, strengthening the hypothesis of
Cowan et al. that the most strongly irradiated planets circulate energy poorly.
Our measurement of the central phase of the eclipse yields e*cos(omega)=0.0003
+/-0.00013, which we regard as being consistent with a circular orbit.
06/2012;
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Kamen O. Todorov,
Drake Deming, Heather A. Knutson,
Adam Burrows,
Pedro V. Sada,
Nicolas B. Cowan,
Eric Agol,
Jean-Michel Desert,
Jonathan J. Fortney,
David Charbonneau,
Gregory Laughlin,
Jonathan Langton,
Adam P. Showman,
and Nikole K. Lewis
[show abstract]
[hide abstract]
ABSTRACT: We analyze Warm Spitzer/Infrared Array Camera observations of the secondary eclipses of three planets, XO-4b, HAT-P-6b, and HAT-P-8b. We measure secondary eclipse amplitudes at 3.6 μm and 4.5 μm for each target. XO-4b exhibits a stronger eclipse depth at 4.5 μm than at 3.6 μm, which is consistent with the presence of a temperature inversion. HAT-P-8b shows a stronger eclipse amplitude at 3.6 μm and is best described by models without a temperature inversion. The eclipse depths of HAT-P-6b can be fitted with models with a small or no temperature inversion. We consider our results in the context of a postulated relationship between stellar activity and temperature inversion and a relationship between irradiation level and planet dayside temperature, as discussed by Knutson et al. and Cowan & Agol, respectively. Our results are consistent with these hypotheses, but do not significantly strengthen them. To measure accurate secondary eclipse central phases, we require accurate ephemerides. We obtain primary transit observations and supplement them with publicly available observations to update the orbital ephemerides of the three planets. Based on the secondary eclipse timing, we set upper boundaries for ecos (ω) for HAT-P-6b, HAT-P-8b, and XO-4b and find that the values are consistent with circular orbits.
The Astrophysical Journal 01/2012; 746(1):111. · 6.02 Impact Factor
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Francois Fressin,
Guillermo Torres,
Frederic Pont, Heather A. Knutson,
David Charbonneau,
Tsevi Mazeh,
Suzanne Aigrain,
Malcolm Fridlund,
Christopher E. Henze,
Tristan Guillot,
and Heike Rauer
[show abstract]
[hide abstract]
ABSTRACT: The detection and characterization of the first transiting super-Earth, CoRoT-7 b, has required an unprecedented effort in terms of telescope time and analysis. Although the star does display a radial-velocity signal at the period of the planet, this has been difficult to disentangle from the intrinsic stellar variability and pinning down the velocity amplitude has been very challenging. As a result, the precise value of the mass of the planet—and even the extent to which it can be considered to be confirmed—has been debated in the recent literature, with six mass measurements published so far based on the same spectroscopic observations, ranging from about 2 to 8 Earth masses. Here we report on an independent validation of the planet discovery using one of the fundamental properties of a transit signal: its achromaticity. We observed four transits of CoRoT-7 b at 4.5 μm and 8.0 μm with the Infrared Array Camera (IRAC) on board the Spitzer Space Telescope in order to determine whether the depth of the transit signal in the near-infrared is consistent with that observed in the CoRoT bandpass, as expected for a planet. We detected the transit and found an average depth of 0.426 ± 0.115 mmag at 4.5 μm, which is in good agreement with the depth of 0.350 ± 0.011 mmag (ignoring limb darkening) found by CoRoT. The observations at 8.0 μm did not yield a significant detection. The 4.5 μm observations place important constraints on the kinds of astrophysical false positives that could mimic the signal. Combining this with additional constraints reported earlier, we performed an exhaustive exploration of possible blend scenarios for CoRoT-7 b using the BLENDER technique. We are able to rule out the vast majority of false positives, and the remaining ones are found to be much less likely than a true transiting planet. We thus validate CoRoT-7 b as a bona fide planet with a very high degree of confidence, independently of any radial-velocity information. Our Spitzer observations have additionally allowed us to significantly improve the ephemeris of the planet, so that future transits should be recoverable well into the next decade. In its warm phase Spitzer is expected to be an essential tool for the validation, along the lines of the present analysis, of transiting planet candidates with shallow signals from CoRoT as well as from the Kepler mission, including potentially rocky planets in the habitable zones of their parent stars.
The Astrophysical Journal 12/2011; 745(1):81. · 6.02 Impact Factor
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Kamen O. Todorov,
Drake Deming, Heather A. Knutson,
Adam Burrows,
Pedro V. Sada,
Nicolas B. Cowan,
Eric Agol,
Jean-Michel Desert,
Jonathan J. Fortney,
David Charbonneau,
Gregory Laughlin,
Jonathan Langton,
Adam P. Showman,
Nikole K. Lewis
[show abstract]
[hide abstract]
ABSTRACT: We have analyzed Warm Spitzer/IRAC observations of the secondary eclipses of
three planets, XO-4b, HAT-P-6b and HAT-P-8b. We measure secondary eclipse
amplitudes at 3.6{\mu}m and 4.5{\mu}m for each target. XO-4b exhibits a
stronger eclipse depth at 4.5{\mu}m than at 3.6{\mu}m, which is consistent with
the presence of a temperature inversion. HAT-P-8b shows a stronger eclipse
amplitude at 3.6{\mu}m, and is best-described by models without a temperature
inversion. The eclipse depths of HAT-P-6b can be fitted with models with a
small or no temperature inversion. We consider our results in the context of a
postulated relationship between stellar activity and temperature inversions and
a relationship between irradiation level and planet dayside temperature, as
discussed by Knutson et al. (2010) and Cowan & Agol (2011), respectively. Our
results are consistent with these hypotheses, but do not significantly
strengthen them. To measure accurate secondary eclipse central phases, we
require accurate ephemerides. We obtain primary transit observations and
supplement them with publicly available observations to update the orbital
ephemerides of the three planets. Based on the secondary eclipse timing, we set
upper boundaries for e cos(\omega) for HAT-P-6b, HAT-P-8b and XO-4b and find
that the values are consistent with circular orbits.
11/2011;
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Jean-Michel Désert,
David Charbonneau,
Brice-Olivier Demory,
Sarah Ballard,
Joshua A. Carter,
Jonathan J. Fortney,
William D. Cochran,
Michael Endl,
Samuel N. Quinn,
Howard T. Isaacson, [......],
Philip Lucas,
Fergal Mullally,
Phillip J. MacQueen,
Geoffrey W. Marcy,
Dimitar D. Sasselov,
Sara Seager,
Martin Still,
Peter Tenenbaum,
Kamal Uddin,
and Joshua N. Winn
[show abstract]
[hide abstract]
ABSTRACT: This paper reports the discovery and characterization of the transiting hot giant exoplanet Kepler-17b. The planet has an orbital period of 1.486 days, and radial velocity measurements from the Hobby-Eberly Telescope show a Doppler signal of 419.5+13.3 –15.6 m s–1. From a transit-based estimate of the host star's mean density, combined with an estimate of the stellar effective temperature T eff = 5630 ± 100 from high-resolution spectra, we infer a stellar host mass of 1.06 ± 0.07 M ☉ and a stellar radius of 1.02 ± 0.03 R ☉. We estimate the planet mass and radius to be M P = 2.45 ± 0.11 M J and R P = 1.31 ± 0.02 R J. The host star is active, with dark spots that are frequently occulted by the planet. The continuous monitoring of the star reveals a stellar rotation period of 11.89 days, eight times the planet's orbital period; this period ratio produces stroboscopic effects on the occulted starspots. The temporal pattern of these spot-crossing events shows that the planet's orbit is prograde and the star's obliquity is smaller than 15°. We detected planetary occultations of Kepler-17b with both the Kepler and Spitzer Space Telescopes. We use these observations to constrain the eccentricity, e, and find that it is consistent with a circular orbit (e < 0.011). The brightness temperatures of the planet's infrared bandpasses are = 1880 ± 100 K and = 1770 ± 150 K. We measure the optical geometric albedo Ag in the Kepler bandpass and find Ag = 0.10 ± 0.02. The observations are best described by atmospheric models for which most of the incident energy is re-radiated away from the day side.
The Astrophysical Journal Supplement Series 11/2011; 197(1):14. · 13.46 Impact Factor
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Jonathan J. Fortney,
Brice-Olivier Demory,
Jean-Michel Désert,
Jason Rowe,
Geoffrey W. Marcy,
Howard Isaacson,
Lars A. Buchhave,
David Ciardi,
Thomas N. Gautier,
Natalie M. Batalha, [......],
Sara Seager,
Debra A. Fischer,
David Koch,
Jack J. Lissauer,
Michael R. Haas,
Martin Still,
Philip Lucas,
Michael Gillon,
Jessie L. Christiansen,
and John C. Geary
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of planet Kepler-12b (KOI-20), which at 1.695 ± 0.030 R J is among the handful of planets with super-inflated radii above 1.65 R J. Orbiting its slightly evolved G0 host with a 4.438 day period, this 0.431 ± 0.041 M J planet is the least irradiated within this largest-planet-radius group, which has important implications for planetary physics. The planet's inflated radius and low mass lead to a very low density of 0.111 ± 0.010 g cm–3. We detect the occultation of the planet at a significance of 3.7σ in the Kepler bandpass. This yields a geometric albedo of 0.14 ± 0.04; the planetary flux is due to a combination of scattered light and emitted thermal flux. We use multiple observations with Warm Spitzer to detect the occultation at 7σ and 4σ in the 3.6 and 4.5 μm bandpasses, respectively. The occultation photometry timing is consistent with a circular orbit at e < 0.01 (1σ) and e < 0.09 (3σ). The occultation detections across the three bands favor an atmospheric model with no dayside temperature inversion. The Kepler occultation detection provides significant leverage, but conclusions regarding temperature structure are preliminary, given our ignorance of opacity sources at optical wavelengths in hot Jupiter atmospheres. If Kepler-12b and HD 209458b, which intercept similar incident stellar fluxes, have the same heavy-element masses, the interior energy source needed to explain the large radius of Kepler-12b is three times larger than that of HD 209458b. This may suggest that more than one radius-inflation mechanism is at work for Kepler-12b or that it is less heavy-element rich than other transiting planets.
The Astrophysical Journal Supplement Series 10/2011; 197(1):9. · 13.46 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We analyze 26 archival Kepler transits of the exo-Neptune HAT-P-11b, supplemented by ground-based transits observed in the blue (B-band) and near-IR (J-band). Both the planet and host star are smaller than previously believed; our analysis yields R p = 4.31R ⊕ ± 0.06R ⊕ , and R s = 0.683R ⊙ ± 0.009R ⊙ , both about 3σ smaller than the discovery values. Our ground-based transit data at wavelengths bracketing the Kepler bandpass serve to check the wavelength dependence of stellar limb darkening, and the J-band transit provides a precise and independent constraint on the transit duration. Both the limb darkening and transit duration from our ground-based data are consistent with the new Kepler values for the system parameters. Our smaller radius for the planet implies that its gaseous envelope can be less extensive than previously believed, being very similar to the H-He envelope of GJ 436b and Kepler-4b. HAT-P-11 is an active star, and signatures of star spot crossings are ubiquitous in the Kepler transit data. We develop and apply a methodology to correct the planetary radius for the presence of both crossed and uncrossed star spots. Star spot crossings are concentrated at phases -0.002 and +0.006. This is consistent with inferences from Rossiter-McLaughlin measurements that the planet transits nearly perpendicular to the stellar equator. We identify the dominant phases of star spot crossings with active latitudes on the star, and we infer that the stellar rotational pole is inclined at about 12 • ± 5 • to the plane of the sky. We point out that precise transit measurements over long durations could in principle allow us to construct a stellar Butterfly diagram, to probe the cyclic evolution of magnetic activity on this active K-dwarf star. Subject headings: stars: planetary systems -transits -techniques: photometric 1. introduction The exo-Neptune HAT-P-11b (Bakos et al. 2010, here-after B10) is prominent among extrasolar planets smaller than Saturn. HAT-P-11b transits a bright star (V=9.59) that lies in the Kepler field (Borucki et al. 2010). Based on its position in a mass-radius diagram (e.g., Figure 14 of B10), HAT-P-11b is likely to have a massive atmo-sphere. Moreover, B10 found good mass and radius agree-ment with metal-rich models for the planet (Baraffe et al. 2008), and the B10 spectroscopic analysis of the host star indicated that it was metal-rich. The planet's atmosphere is therefore likely to exhibit a significant molecular ab-sorption spectrum during transit and/or eclipse. It is a tempting target for future spectroscopic characteriza-tion, for example using precise ground-based spectropho-tometry (e.g., Bean et al. 2010) in combination with HST (Pont et al. 2009), and/or Warm Spitzer (Desert et al. 2011). Prior to such efforts, it is important to improve our current knowledge of the system parameters and opti-cal planetary radius by examining the Kepler data. Based on photometric variations of the star, B10 con-cluded that star spots were common on the stellar pho-tosphere. Rossiter-McLaughlin observations of the sys-tem (Winn et al. 2010; Hirano et al. 2011) indicate that the planet's orbital angular momentum vector is nearly perpendicular to the orbital angular momentum vector of the star. Winn et al. (2010) predicted that this mis-alignment would produce a characteristic signature in the spot-crossing patterns seen during transit, and this should be quite evident in the Kepler data. In this paper, we report an analysis of Q0-Q2 archival Kepler data for transits of HAT-P-11b, supplemented with new ground-based transit data at wavelengths bracketing the Kepler bandpass. The potential benefits of ground-based transit photometry as a complement to Kepler have been emphasized by Colon & Ford (2009).
08/2011;
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[show abstract]
[hide abstract]
ABSTRACT: We analyze 26 archival Kepler transits of the exo-Neptune HAT-P-11b,
supplemented by ground-based transits observed in the blue (B-band) and near-IR
(J-band). Both the planet and host star are smaller than previously believed;
our analysis yields Rp=4.31 +/-0.06 Earth-radii, and Rs = 0.683 +/-0.009 solar
radii, both about 3-sigma smaller than the discovery values. Our ground-based
transit data at wavelengths bracketing the Kepler bandpass serve to check the
wavelength dependence of stellar limb darkening, and the J-band transit
provides a precise and independent constraint on the transit duration. Both the
limb darkening and transit duration from our ground-based data are consistent
with the new Kepler values for the system parameters. Our smaller radius for
the planet implies that its gaseous envelope can be less extensive than
previously believed, being very similar to the H-He envelope of GJ436b and
Kepler-4b. HAT-P-11 is an active star, and signatures of star spot crossings
are ubiquitous in the Kepler transit data. We develop and apply a methodology
to correct the planetary radius for the presence of both crossed and uncrossed
star spots. Star spot crossings are concentrated at phases -0.002 and +0.006.
This is consistent with inferences from Rossiter-McLaughlin measurements that
the planet transits nearly perpendicular to the stellar equator. We identify
the dominant phases of star spot crossings with active latitudes on the star,
and we infer that the stellar rotational pole is inclined at about 12 +/-5
degrees to the plane of the sky. We point out that precise transit measurements
over long durations could in principle allow us to construct a stellar
Butterfly diagram, to probe the cyclic evolution of magnetic activity on this
active K-dwarf star.
07/2011;
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Lars A. Buchhave,
David W. Latham,
Joshua A. Carter,
Jean-Michel Désert,
Guillermo Torres,
Elisabeth R. Adams,
Stephen T. Bryson,
David B. Charbonneau,
David R. Ciardi,
Craig Kulesa, [......],
David G. Koch,
Jeffrey Kolodziejczak,
Jack J. Lissauer,
Pavel Machalek,
Fergal Mullally,
Martin D. Still,
Samuel N. Quinn,
Sara Seager,
Susan E. Thompson,
Jeffrey Van Cleve
[show abstract]
[hide abstract]
ABSTRACT: We present the discovery of a hot Jupiter transiting an F star in a close
visual (0.3" sky projected angular separation) binary system. The dilution of
the host star's light by the nearly equal magnitude stellar companion (~ 0.5
magnitudes fainter) significantly affects the derived planetary parameters, and
if left uncorrected, leads to an underestimate of the radius and mass of the
planet by 10% and 60%, respectively. Other published exoplanets, which have not
been observed with high-resolution imaging, could similarly have unresolved
stellar companions and thus have incorrectly derived planetary parameters.
Kepler-14b (KOI-98) has a period of P = 6.790 days and correcting for the
dilution, has a mass of Mp = 8.40 +0.19-0.18 MJ and a radius of Rp = 1.136
+0.073-0.054 RJ, yielding a mean density of rho = 7.1 +- 1.1 g cm-3.
06/2011;
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Heather A. Knutson,
Nikku Madhusudhan,
Nicolas B. Cowan,
Jessie L. Christiansen,
Eric Agol,
Drake Deming,
Jean-Michel Désert,
David Charbonneau,
Gregory W. Henry,
Derek Homeier,
Jonathan Langton,
Gregory Laughlin,
and Sara Seager
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ABSTRACT: In this paper, we describe a uniform analysis of eight transits and eleven secondary eclipses of the extrasolar planet GJ 436b obtained in the 3.6, 4.5, and 8.0 μm bands using the IRAC instrument on the Spitzer Space Telescope between UT 2007 June 29 and UT 2009 February 4. We find that the best-fit transit depths for visits in the same bandpass can vary by as much as 8% of the total (4.7σ significance) from one epoch to the next. Although we cannot entirely rule out residual detector effects or a time-varying, high-altitude cloud layer in the planet's atmosphere as the cause of these variations, we consider the occultation of active regions on the star in a subset of the transit observations to be the most likely explanation. We find that for the deepest 3.6 μm transit the in-transit data have a higher standard deviation than the out-of-transit data, as would be expected if the planet occulted a star spot. We also compare all published transit observations for this object and find that transits observed in the infrared typically have smaller timing offsets than those observed in visible light. In this case, the three deepest Spitzer transits are all measured within a period of five days, consistent with a single epoch of increased stellar activity. We reconcile the presence of magnetically active regions with the lack of significant visible or infrared flux variations from the star by proposing that the star's spin axis is tilted with respect to our line of sight and that the planet's orbit is therefore likely to be misaligned. In contrast to the results reported by Beaulieu et al., we find no convincing evidence for methane absorption in the planet's transmission spectrum. If we exclude the transits that we believe to be most affected by stellar activity, we find that we prefer models with enhanced CO and reduced methane, consistent with GJ 436b's dayside composition from Stevenson et al. It is also possible that all transits are significantly affected by this activity, in which case it may not be feasible to characterize the planet's transmission spectrum using broadband photometry obtained over multiple epochs. These observations serve to illustrate the challenges associated with transmission spectroscopy of planets orbiting late-type stars; we expect that other systems, such as GJ 1214, may display comparably variable transit depths. We compare the limb-darkening coefficients predicted by PHOENIX and ATLAS stellar atmosphere models and discuss the effect that these coefficients have on the measured planet-star radius ratios given GJ 436b's near-grazing transit geometry. Our measured 8 μm secondary eclipse depths are consistent with a constant value, and we place a 1σ upper limit of 17% on changes in the planet's dayside flux in this band. These results are consistent with predictions from general circulation models for this planet, which find that the planet's dayside flux varies by a few percent or less in the 8 μm band. Averaging over the eleven visits gives us an improved estimate of 0.0452% ± 0.0027% for the secondary eclipse depth; we also examine residuals from the eclipse ingress and egress and place an upper limit on deviations caused by a non-uniform surface brightness for GJ 436b. We combine timing information from our observations with previously published data to produce a refined orbital ephemeris and determine that the best-fit transit and eclipse times are consistent with a constant orbital period. We find that the secondary eclipse occurs at a phase of 0.58672 ± 0.00017, corresponding to ecos (ω) = 0.13754 ± 0.00027, where e is the planet's orbital eccentricity and ω is the longitude of pericenter. We also present improved estimates for other system parameters, including the orbital inclination, a/R , and the planet-star radius ratio.
The Astrophysical Journal 06/2011; 735(1):27. · 6.02 Impact Factor
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Jean-Michel Desert,
David Charbonneau,
Jonathan J. Fortney,
Nikku Madhusudhan, Heather A. Knutson,
Francois Fressin,
Drake Deming,
William J. Borucki,
Timothy M. Brown,
Douglas Caldwell,
Eric B. Ford,
Ronald L. Gilliland,
David W. Latham,
Geoffrey W. Marcy,
Sara Seager,
the Kepler Science Team
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ABSTRACT: This paper reports the detection and the measurements of occultations of the
two transiting hot giant exoplanets Kepler-5b and Kepler-6b by their parent
stars. The observations are obtained in the near infrared with Spitzer Space
Telescope and at optical wavelengths by combining more than a year of Kepler
photometry. The investigation consists of constraining the eccentricities of
these systems and of obtaining broad band emergent spectra for individual
planets. For both targets, the occultations are detected at 3 sigma level at
each wavelength with mid-occultation times consistent with circular orbits. The
brightness temperatures of these planets are deduced from the infrared
observations and reach T=1930+/-100K and T=1660+/-120K for Kepler-5b and
Kepler-6b respectively. We measure optical geometric albedos A_g in the Kepler
bandpass and find A_g=0.12+/-0.04 for Kepler-5b and A_g=0.11+/-0.04 for
Kepler-6b leading to an upper limit for the Bond albedo of A_B < 0.17 in both
cases. The observations for both planets are best described by models for which
most of the incident energy is redistributed on the dayside, with only less
than 10% of the absorbed stellar flux redistributed to the night side of these
planets. The data for Kepler-5b favor a model without a temperature inversion,
whereas for Kepler-6b they do not allow distinguishing between models with and
without inversion.
02/2011;
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Ingrid M. Beerer, Heather A. Knutson,
Adam Burrows,
Jonathan J. Fortney,
Eric Agol,
David Charbonneau,
Nicolas B. Cowan,
Drake Deming,
Jean-Michel Desert,
Jonathan Langton,
Gregory Laughlin,
Nikole K. Lewis,
and Adam P. Showman
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ABSTRACT: We present photometry of the giant extrasolar planet WASP-4b at 3.6 and 4.5 μm taken with the Infrared Array Camera on board the Spitzer Space Telescope as part of Spitzer's extended warm mission. We find secondary eclipse depths of 0.319% ± 0.031% and 0.343% ± 0.027% for the 3.6 and 4.5 μm bands, respectively, and show model emission spectra and pressure-temperature profiles for the planetary atmosphere. These eclipse depths are well fit by model emission spectra with water and other molecules in absorption, similar to those used for TrES-3 and HD 189733b. Depending on our choice of model, these results indicate that this planet has either a weak dayside temperature inversion or no inversion at all. The absence of a strong thermal inversion on this highly irradiated planet is contrary to the idea that highly irradiated planets are expected to have inversions, perhaps due the presence of an unknown absorber in the upper atmosphere. This result might be explained by the modestly enhanced activity level of WASP-4b's G7V host star, which could increase the amount of UV flux received by the planet, therefore reducing the abundance of the unknown stratospheric absorber in the planetary atmosphere as suggested in Knutson et al. We also find no evidence for an offset in the timing of the secondary eclipse and place a 2σ upper limit on |ecos ω| of 0.0024, which constrains the range of tidal heating models that could explain this planet's inflated radius.
The Astrophysical Journal 12/2010; 727(1):23. · 6.02 Impact Factor
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ABSTRACT: We present observations of six transits and six eclipses of the transiting planet system HD 189733 taken with the Spitzer Space Telescope's Infrared Array Camera (IRAC) at 8 μm, as well as a re-analysis of previously published data. We use several novel techniques in our data analysis, the most important of which is a new correction for the detector "ramp" variation with a double-exponential function, which performs better and is a better physical model for this detector variation. Our main scientific findings are (1) an upper limit on the variability of the dayside planet flux of 2.7% (68% confidence); (2) the most precise set of transit times measured for a transiting planet, with an average accuracy of 3 s; (3) a lack of transit-timing variations, excluding the presence of second planets in this system above 20% of the mass of Mars in low-order mean-motion resonance at 95% confidence; (4) a confirmation of the planet's phase variation, finding the night side is 64% as bright as the day side, as well as an upper limit on the nightside variability of 17% (68% confidence); (5) a better correction for stellar variability at 8 μm causing the phase function to peak 3.5 hr before secondary eclipse, confirming that the advection and radiation timescales are comparable at the 8 μm photosphere; (6) variation in the depth of transit, which possibly implies variations in the surface brightness of the portion of the star occulted by the planet, posing a fundamental limit on non-simultaneous multi-wavelength transit absorption measurements of planet atmospheres; (7) a measurement of the infrared limb darkening of the star, which is in good agreement with stellar atmosphere models; (8) an offset in the times of secondary eclipse of 69 s, which is mostly accounted for by a 31 s light-travel time delay and 33 s delay due to the shift of ingress and egress by the planet hot spot; this confirms that the phase variation is due to an offset hot spot on the planet; (9) a retraction of the claimed eccentricity of this system due to the offset of secondary eclipse, which is now just an upper limit; and (10) high-precision measurements of the parameters of this system. These results were enabled by the exquisite photometric precision of Spitzer IRAC; for repeat observations the scatter is less than 0.35 mmag over the 590 day timescale of our observations after decorrelating with detector parameters.
The Astrophysical Journal 09/2010; 721(2):1861. · 6.02 Impact Factor
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ABSTRACT: We discovered evidence for a possible additional 0.75 R_Earth transiting planet in the NASA EPOXI observations of the known M dwarf exoplanetary system GJ 436. Based on an ephemeris determined from the EPOXI data, we predicted a transit event in an extant Spitzer Space Telescope 8 micron data set of this star. Our subsequent analysis of those Spitzer data confirmed the signal of the predicted depth and at the predicted time, but we found that the transit depth was dependent on the aperture used to perform the photometry. Based on these suggestive findings, we gathered new Warm Spitzer Observations of GJ 436 at 4.5 microns spanning a time of transit predicted from the EPOXI and Spitzer 8 micron candidate events. The 4.5 micron data permit us to rule out a transit at high confidence, and we conclude that the earlier candidate transit signals resulted from correlated noise in the EPOXI and Spitzer 8 micron observations. In the course of this investigation, we developed a novel method for correcting the intrapixel sensitivity variations of the 3.6 and 4.5 micron channels of the Infrared Array Camera (IRAC) instrument. We demonstrate the sensitivity of Warm Spitzer observations of M dwarfs to confirm sub-Earth sized planets. Our analysis will inform similar work that will be undertaken to use Warm Spitzer observations to confirm rocky planets discovered by the Kepler mission. Comment: 22 pages, 8 figures, accepted for publication in PASP
09/2010;
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ABSTRACT: We present evidence for a correlation between the observed properties of hot Jupiter emission spectra and the activity levels of the host stars measured using Ca II H & K emission lines. We find that planets with dayside emission spectra that are well-described by standard 1D atmosphere models with water in absorption (HD 189733, TrES-1, TrES-3, WASP-4) orbit chromospherically active stars, while planets with emission spectra that are consistent with the presence of a strong high-altitude temperature inversion and water in emission orbit quieter stars. We estimate that active G and K stars have Lyman alpha fluxes that are typically a factor of 4-7 times higher than quiet stars with analogous spectral types, and propose that the increased UV flux received by planets orbiting active stars destroys the compounds responsible for the formation of the observed temperature inversions. In this paper we also derive a model-independent method for differentiating between these two atmosphere types using the secondary eclipse depths measured in the 3.6 and 4.5 micron bands on the Spitzer Space Telescope, and argue that the observed correlation is independent of the inverted/non-inverted paradigm for classifying hot Jupiter atmospheres. Comment: 9 pages, 5 figures, accepted for publication in ApJ. The updated paper includes spectra for ten additional systems and a new section discussing the connection between chromospheric activity and UV flux
04/2010;
