Wasp-8b: Characterization of A Cool And Eccentric Exoplanet With Spitzer

Authors

P. Cubillos; J. Harrington; N. Madhusudhan; K. B. Stevenson; R. A. Hardy; J. Blecic; D. R. Anderson; M. Hardin;C. J. Campo

Comments

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Abbreviated Journal Title

Astrophys. J.

Keywords

planetary systems; stars: individual (WASP-8); techniques: photometric; TRANSITING EXTRASOLAR PLANETS; THERMAL PHASE VARIATIONS; DOPPLER; FOLLOW-UP; 8 MU-M; HOT JUPITERS; HD 189733B; GJ 436B; SPACE-TELESCOPE; LIGHT CURVES; TRANSMISSION SPECTRUM; Astronomy & Astrophysics

Abstract

WASP-8b has 2.18 times Jupiter's mass and is on an eccentric (e = 0.31) 8.16 day orbit. With a time-averaged equilibrium temperature of 948 K, it is one of the least-irradiated hot Jupiters observed with the Spitzer Space Telescope. We have analyzed six photometric light curves of WASP-8b during secondary eclipse observed in the 3.6, 4.5, and 8.0 mu m Infrared Array Camera bands. The eclipse depths are 0.113% +/- 0.018%, 0.069% +/- 0.007%, and 0.093% +/- 0.023%, respectively, giving respective brightness temperatures of 1552, 1131, and 938 K. We characterized the atmospheric thermal profile and composition of the planet using a line-by-line radiative transfer code and a Markov-chain Monte Carlo sampler. The data indicated no thermal inversion, independently of any assumption about chemical composition. We noted an anomalously high 3.6 mu m brightness temperature (1552 K); by modeling the eccentricity-caused thermal variation, we found that this temperature is plausible for radiative timescales less than similar to 10(2) hr. However, as no model spectra fit all three data points well, the temperature discrepancy remains as an open question.

Journal Title

Astrophysical Journal

Volume

768

Issue/Number

1

Publication Date

1-1-2013

Document Type

Article

Language

English

First Page

12

WOS Identifier

WOS:000317960500042

ISSN

0004-637X

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