192 research outputs found
On the Presence of Water and Global Circulation in the Transiting Planet HD 189733b
Detailed models are compared to recent infrared observations of the nearby
extrasolar planet, HD 189733b. It is demonstrated that atmospheric water is
present and that the planet's day side has a non-isothermal structure down to
gas pressures of ~ 0.1 bars. Furthermore, model spectra with different amounts
of CO are compared to the observations and an atmosphere absent of CO is
excluded at roughly 2-sigma. Constraining the CO concentration beyond that is
unfortunately not possible with the current Spitzer photometry. However,
radically enhanced (or depleted) metal abundances are unlikely and the basic
composition of this planet is probably similar to that of its host star. When
combined with Spitzer observations, a recent ground-based upper limit for the
K-band day side flux allows one to estimate the day-to-night energy
redistribution efficiency to be ~ 43%.Comment: accepted (2008 Feb. 5), ApJ Letter
Two Classes of Hot Jupiters
We identify two classes of transiting planet, based on their equilibrium
temperatures and Safronov numbers. We examine various possible explanations for
the dichotomy. It may reflect the influence of planet or planetesimal
scattering in determining when planetary migration stops. Another possibility
is that some planets lose more mass to evaporation than others. If this
evaporation process preferentially removes Helium from the planet, the
consequent reduction in the mean molecular weight may explain why some planets
have anomalously large radii.Comment: 35 pages, 16 figures in Preprint format. Submitted to Ap
The Influence of Host Star Spectral Type on Ultra-Hot Jupiter Atmospheres
Ultra-hot Jupiters are the most highly irradiated gas giant planets, with
equilibrium temperatures from 2000 to over 4000 K. Ultra-hot Jupiters are
amenable to characterization due to their high temperatures, inflated radii,
and short periods, but their atmospheres are atypical for planets in that the
photosphere possesses large concentrations of atoms and ions relative to
molecules. Here we evaluate how the atmospheres of these planets respond to
irradiation by stars of different spectral type. We find that ultra-hot
Jupiters exhibit temperature inversions that are sensitive to the spectral type
of the host star. The slope and temperature range across the inversion both
increase as the host star effective temperature increases due to enhanced
absorption at short wavelengths and low pressures. The steep temperature
inversions in ultra-hot Jupiters around hot stars result in increased thermal
dissociation and ionization compared to similar planets around cooler stars.
The resulting increase in H opacity leads to a transit spectrum that has
muted absorption features. The emission spectrum, however, exhibits a large
contrast in brightness temperature, a signature that will be detectable with
both secondary eclipse observations and high-dispersion spectroscopy. We also
find that the departures from local thermodynamic equilibrium in the stellar
atmosphere can affect the degree of heating caused by atomic metals in the
planet's upper atmosphere. Additionally, we further quantify the significance
of heating by different opacity sources in ultra-hot Jupiter atmospheres.Comment: 13 pages, 9 figures, 2 tables. Accepted for publication in Ap
The PHOENIX Exoplanet Retrieval Algorithm and Using H Opacity as a Probe in Ultra-hot Jupiters
Atmospheric retrievals are now a standard tool to analyze observations of
exoplanet atmospheres. This data-driven approach quantitatively compares
atmospheric models to observations in order to estimate atmospheric properties
and their uncertainties. In this paper, we introduce a new retrieval package,
the PHOENIX Exoplanet Retrieval Analysis (PETRA). PETRA places the PHOENIX
atmosphere model in a retrieval framework, allowing us to combine the strengths
of a well-tested and widely-used atmosphere model with the advantages of
retrieval algorithms. We validate PETRA by retrieving on simulated data for
which the true atmospheric state is known. We also show that PETRA can
successfully reproduce results from previously published retrievals of WASP-43b
and HD 209458b. For the WASP-43b results, we show the effect that different
line lists and line profile treatments have on the retrieved atmospheric
properties. Lastly, we describe a novel technique for retrieving the
temperature structure and density in ultra-hot Jupiters using H
opacity, allowing us to probe atmospheres devoid of most molecular features
with JWST.Comment: 17 pages, 18 figures. Accepted for publication in A
Warm Ice Giant GJ 3470b. I. A Flat Transmission Spectrum Indicates a Hazy, Low-methane, and/or Metal-rich Atmosphere
We report our spectroscopic investigation of the transiting ice giant GJ
3470b's atmospheric transmission, and the first results of extrasolar planet
observations from the new Keck/MOSFIRE spectrograph. We measure a planet/star
radius ratio of Rp/Rs = 0.0789 +/- 0.0020 in a bandpass from 2.09-2.36 micron
and in six narrower bands across this wavelength range. When combined with
existing broadband photometry, these measurements rule out cloud-free
atmospheres in chemical equilibrium assuming either solar abundances (5.4 sigma
confidence) or a moderate level of metal enrichment (50x solar abundances, 3.8
sigma), confirming previous results that such models are not representative for
cool, low-mass, externally irradiated extrasolar planets. Current measurements
are consistent with a flat transmission spectrum, which suggests that the
atmosphere is explained by high-altitude clouds and haze, disequilibrium
chemistry, unexpected abundance patterns, or the atmosphere is extremely
metal-rich (>200x solar). Because GJ 3470b's low bulk density sets an upper
limit on the planet's atmospheric enrichment of <300x solar, the atmospheric
mean molecular weight must be <9. Thus, if the atmosphere is cloud-free its
spectral features should be detectable with future observations. Transit
observations at shorter wavelengths will provide the best opportunity to
discriminate between plausible scenarios. We obtained optical spectroscopy with
the GMOS spectrograph, but these observations exhibit large systematic
uncertainties owing to thin, persistent cirrus conditions. Finally, we also
provide the first detailed look at the steps necessary for well-calibrated
MOSFIRE observations, and provide advice for future observations with this
instrument.Comment: Accepted to A&A. Light curves will be available at CDS (or download
arXiv tarball
Re-evaluating Hot Jupiter WASP-12b: An Update
The hot Jupiter WASP-12b is one of the largest, hottest, and best-studied
extrasolar planets. We revisit our recent analysis of WASP-12b's emission
spectrum in light of near-infrared spectroscopic measurements which have been
claimed to support either a hydride-dominated or carbon-rich atmospheric
composition. We show that this new spectrum is still consistent with a
featureless blackbody, indicating a nearly isothermal photosphere on the
planet's day side. Thus the ensemble of occultation measurements for WASP-12b
is still insufficient to constrain the planet's atmospheric composition.Comment: 4 pages, 2 figures. Submitted as Proceedings to the ROPACS meeting
"Hot Planets and Cool Stars" (Nov. 2012, Garching),
http://www.mpe.mpg.de/events/ropacs-2012/Home.htm
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