Letter to the Editor

H-band thermal emission from the 19-h period planet WASP-19b ^*,**

D. R. Anderson¹, M. Gillon^2,3, P. F. L. Maxted¹, T. S. Barman⁴, A. Collier Cameron⁵, C. Hellier¹, D. Queloz³, B. Smalley¹ and A. H. M. J. Triaud³

¹ Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK e-mail: dra@astro.keele.ac.uk
² Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 17, Bat. B5C, 4000 Liège, Belgium
³ Observatoire de Genève, Université de Genève, 51 Chemin des Maillettes, 1290 Sauverny, Switzerland
⁴ Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001, USA
⁵ School of Physics and Astronomy, University of St. Andrews, North Haugh, Fife KY16 9SS, UK

Received: 9 February 2010
Accepted: 10 March 2010

Abstract

We present the first ground-based detection of thermal emission from an exoplanet in the H-band. Using HAWK-I on the VLT, we observed an occultation of WASP-19b by its G8V-type host star. WASP-19b is a Jupiter-mass planet with an orbital period of only 19 h, and thus, being highly irradiated, is expected to be hot. We measure an H-band occultation depth of 0.259%, which corresponds to an H-band brightness temperature of T_H = 2580 ± 125 K. A cloud-free model of the planet's atmosphere, with no redistribution of energy from day-side to night-side, under predicts the planet/star flux density ratio by a factor of two. As the stellar parameters, and thus the level of planetary irradiation, are well-constrained by measurement, it is likely that our model of the planet's atmosphere is too simple.