The Spitzer search for the transits of HARPS low-mass planets^*

I. No transit for the super-Earth HD 40307b

¹ Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 17, Bat. B5C, 4000 Liège, Belgium e-mail: michael.gillon@ulg.ac.be
² Observatoire de Genève, Université de Genève, 51 Chemin des Maillettes, 1290 Sauverny, Switzerland
³ Planetary Systems Branch, Code 693, NASA/Goddard Space Flight Center, MD 20771 Greenbelt, USA
⁴ Department of Earth, Atmospheric and Planetary Sciences, Department of Physics, Massachusetts Institute of Technology, 77 Massachusetts Ave., MA 02139 Cambridge, USA

Received: 27 January 2010
Accepted: 14 April 2010

Abstract

We used Spitzer and its IRAC camera to search for the transit of the super-Earth HD 40307b. The hypothesis that the planet transits could not be firmly discarded from our first photometric monitoring of a transit window because of the uncertainty coming from the modeling of the photometric baseline. To obtain a firm result, two more transit windows were observed and a global Bayesian analysis of the three IRAC time series and the HARPS radial velocities was performed. Unfortunately, the hypothesis that the planet transited during the observed phase window is firmly rejected, while the probability that the planet does transit but that the eclipse was missed by our observations is nearly negligible (0.26%).