Hot Jupiter WASP-10b Orbit Refined

Detection of the secondary eclipse of WASP-10b in the Ks-band

Authors:

Cruz et al

Abstract:

WASP-10b, a non-inflated hot Jupiter, was discovered around a K-dwarf in a near circular orbit (∼0.06). Since its discovery in 2009, different published parameters for this system have led to a discussion about the size, density, and eccentricity of this exoplanet. In order to test the hypothesis of a circular orbit for WASP-10b, we have observed its secondary eclipse in the Ks-band, where the contribution of planetary light is high enough to be detected from the ground. Observations were performed with the OMEGA2000 instrument at the 3.5-meter telescope at Calar Alto (Almer\'ia, Spain), in staring mode during 5.4 continuous hours, with the telescope defocused, monitoring the target during the expected secondary eclipse. A relative light curve was generated and corrected from systematic effects, using the Principal Component Analysis (PCA) technique. The final light curve was fitted using a transit model to find the eclipse depth and a possible phase shift. The best model obtained from the Markov Chain Monte Carlo analysis resulted in an eclipse depth of ΔF of 0.137%+0.013%−0.019% and a phase offset of Δϕ of −0.0028+0.0005−0.0004. The eclipse phase offset derived from our modeling has systematic errors that were not taken into account and should not be considered as evidence of an eccentric orbit. The offset in phase obtained leads to a value for |ecosω| of 0.0044. The derived eccentricity is too small to be of any significance.

Water Vapor Detected in Eclipse Spectrum of hot Jupiter HD 189733b

Water vapor in the spectrum of the extrasolar planet HD 189733b: 2. The eclipse

Authors:

Crouzet et al

Abstract:

Spectroscopic observations of exoplanets are crucial to infer the composition and properties of their atmospheres. HD 189733b is one of the most extensively studied exoplanets and is a corner stone for hot Jupiter models. In this paper, we report the day-side emission spectrum of HD 189733b in the wavelength range 1.1 to 1.7 μm obtained with the Hubble Space Telescope Wide Field Camera 3 in spatial scan mode. The quality of the data is such that even a straightforward analysis yields a high precision Poisson noise limited spectrum: the median 1-σ uncertainty is 57 ppm per 0.02 μm bin. We also build a white-light curve correcting for systematic effects and derive an absolute eclipse depth of 96±39 ppm. The resulting spectrum shows marginal evidence for water vapor absorption, but can also be well explained by a blackbody spectrum. However, the combination of these WFC3 data with previous Spitzer photometric observations is best explained by a day-side atmosphere of HD 189733b with no thermal inversion and a nearly solar or sub-solar H2O abundance in a cloud-free atmosphere. Alternatively, this apparent sub-solar abundance may be the result of clouds or hazes which future studies need to investigate.

Atmospheric Refraction Places Limits on Probing Habitable Worlds

IMPACT OF ATMOSPHERIC REFRACTION: HOW DEEPLY CAN WE PROBE EXO-EARTH'S ATMOSPHERES DURING PRIMARY ECLIPSE OBSERVATIONS?

Authors:

Bétrémieux et al

Abstract:

Most models used to predict or fit exoplanet transmission spectra do not include all the effects of atmospheric refraction. Namely, the angular size of the star with respect to the planet can limit the lowest altitude, or highest density and pressure, probed during primary eclipses as no rays passing below this critical altitude can reach the observer. We discuss this geometrical effect of refraction for all exoplanets and tabulate the critical altitude, density, and pressure for an exoplanet identical to Earth with a 1 bar N2/O2 atmosphere as a function of both the incident stellar flux (Venus, Earth, and Mars-like) at the top of the atmosphere and the spectral type (O5-M9) of the host star. We show that such a habitable exo-Earth can be probed to a surface pressure of 1 bar only around the coolest stars. We present 0.4-5.0 μm model transmission spectra of Earth's atmosphere viewed as a transiting exoplanet, and show how atmospheric refraction modifies the transmission spectrum depending on the spectral type of the host star. We demonstrate that refraction is another phenomenon that can potentially explain flat transmission spectra over some spectral regions.

Inferring Exoplanet Atmospheres From Spectra may be Premature

Broadband Eclipse Spectra of Exoplanets are Featureless

Authors:

Hansen et al

Abstract:

Spectral retrieval methods leverage features in emission spectra to constrain the atmospheric composition and structure of transiting exoplanets. Most of the observed emission spectra consist of broadband photometric observations at a small number of wavelengths. We compare the Bayesian Information Criterion (BIC) of blackbody fits and spectral retrieval fits for all planets with eclipse measurements in multiple thermal wavebands, typically hot Jupiters with 2-4 observations. If the published error bars are taken at face value, then eight planets are significantly better fit by a spectral model than by a blackbody. In this under-constrained regime, however, photometric uncertainties directly impact one's ability to constrain atmospheric properties. By considering the handful of planets for which eclipse measurements have been repeated and/or reanalyzed, we obtain an empirical estimate of systematic uncertainties for broadband eclipse depths obtained with the Spitzer Space Telescope: sigma_sys = 5E-4. When this systematic uncertainty is added in quadrature to published uncertainties, the Bayesian evidence for spectral features disappears: blackbodies have better BIC for all planets. Stratospheric inversions, high C/O ratios, disequilibrium chemistry, and He-dominated atmospheres have been inferred from spectral features in broadband eclipse photometry, and are therefore suspect. We conclude that statements about atmospheric composition and structure based solely on photometry are premature.