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Statistical Analysis of Hubble/WFC3 Transit Spectroscopy of Extrasolar Planets

Fu, Guangwei and Deming, Drake and Knutson, Heather and Madhusudhan, Nikku and Mandell, Avi and Fraine, Jonathan (2017) Statistical Analysis of Hubble/WFC3 Transit Spectroscopy of Extrasolar Planets. Astrophysical Journal Letters, 847 (2). Art. No. L22. ISSN 2041-8213. doi:10.3847/2041-8213/aa8e40.

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Transmission spectroscopy provides a window to study exoplanetary atmospheres, but that window is fogged by clouds and hazes. Clouds and haze introduce a degeneracy between the strength of gaseous absorption features and planetary physical parameters such as abundances. One way to break that degeneracy is via statistical studies. We collect all published HST/WFC3 transit spectra for 1.1–1.65 μm water vapor absorption and perform a statistical study on potential correlations between the water absorption feature and planetary parameters. We fit the observed spectra with a template calculated for each planet using the Exo-transmit code. We express the magnitude of the water absorption in scale heights, thereby removing the known dependence on temperature, surface gravity, and mean molecular weight. We find that the absorption in scale heights has a positive baseline correlation with planetary equilibrium temperature; our hypothesis is that decreasing cloud condensation with increasing temperature is responsible for this baseline slope. However, the observed sample is also intrinsically degenerate in the sense that equilibrium temperature correlates with planetary mass. We compile the distribution of absorption in scale heights, and we find that this distribution is closer to log-normal than Gaussian. However, we also find that the distribution of equilibrium temperatures for the observed planets is similarly log-normal. This indicates that the absorption values are affected by observational bias, whereby observers have not yet targeted a sufficient sample of the hottest planets.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Deming, Drake0000-0001-5727-4094
Knutson, Heather0000-0002-0822-3095
Madhusudhan, Nikku0000-0002-4869-000X
Mandell, Avi0000-0002-8119-3355
Fraine, Jonathan0000-0003-0910-5805
Additional Information:© 2017 The American Astronomical Society. Received 2017 August 30; revised 2017 September 20; accepted 2017 September 20; published 2017 October 3. We thank an anonymous referee and also Dr. Nikole Lewis and Dr. Hannah Wakeford for insightful comments that helped us improve this Letter.
Group:Astronomy Department
Subject Keywords:planets and satellites: atmospheres; techniques: spectroscopic
Issue or Number:2
Record Number:CaltechAUTHORS:20171002-134851395
Persistent URL:
Official Citation:Guangwei Fu et al 2017 ApJL 847 L22
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:81957
Deposited By: Tony Diaz
Deposited On:02 Oct 2017 23:13
Last Modified:15 Nov 2021 19:47

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