Detection of a transit of the super-Earth 55 Cancri e with warm Spitzer^⋆

¹ Department of Earth, Atmospheric and Planetary Sciences, Department of Physics, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, USA
e-mail: demory@mit.edu
² Institut d’Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 17, Bat. B5C, 4000 Liège, Belgium
³ Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
⁴ Observatoire de Genève, Université de Genève, 51 Chemin des Maillettes, 1290 Sauverny, Switzerland
⁵ Planetary Science Group, Department of Physics, University of Central Florida, Orlando, FL 32816-2385, USA

Received: 3 May 2011
Accepted: 31 July 2011

Abstract

We report on the detection of a transit of the super-Earth 55 Cnc e with warm Spitzer in IRAC’s 4.5 μm band. Our MCMC analysis includes an extensive modeling of the systematic effects affecting warm Spitzer photometry, and yields a transit depth of 410 ± 63 ppm, which translates to a planetary radius of $\mathrm{2.0}{\mathrm{8}}_{-0.17}^{\mathrm{+}\mathrm{0.16}}{\mathit{R}}_{\mathrm{\oplus }}$ as measured in IRAC 4.5 μm channel. A planetary mass of $\mathrm{7.8}{\mathrm{1}}_{-0.53}^{\mathrm{+}\mathrm{0.58}}{\mathit{M}}_{\mathrm{\oplus }}$ is derived from an extensive set of radial-velocity data, yielding a mean planetary density of $\mathrm{4.7}{\mathrm{8}}_{-1.20}^{\mathrm{+}\mathrm{1.31}}$ g cm^-3. Thanks to the brightness of its host star (V = 6, K = 4), 55 Cnc e is a unique target for the thorough characterization of a super-Earth orbiting around a solar-type star.