Detection of the secondary eclipse of Qatar-1b in the Ks band^⋆,⋆⋆

¹ Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo (IAG/USP), São Paulo, Brazil
e-mail: patricia.cruz@usp.br
² Depto. de Astrofísica, Centro de Astrobiología (INTA-CSIC), ESAC campus, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Spain
³ European Southern Observatory (ESO), Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago de Chile, Chile
⁴ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁵ Department of Astronomy and Astrophysics, University of California, 1156 High Street, Santa Cruz, CA 95064, USA

Received: 16 April 2015
Accepted: 21 August 2016

Abstract

Aims. Qatar-1b is a close-orbiting hot Jupiter (R_p ≃ 1.18 R_J, M_p ≃ 1.33 M_J) around a metal-rich K-dwarf, with orbital separation and period of 0.023 AU and 1.42 days. We have observed the secondary eclipse of this exoplanet in the Ks band with the objective of deriving a brightness temperature for the planet and providing further constraints to the orbital configuration of the system.

Methods. We obtained near-infrared photometric data from the ground by using the OMEGA2000 instrument at the 3.5 m telescope at Calar Alto (Spain) in staring mode, with the telescope defocused. We have used principal component analysis (PCA) to identify correlated systematic trends in the data. A Markov chain Monte Carlo analysis was performed to model the correlated systematics and fit for the secondary eclipse of Qatar-1b using a previously developed occultation model. We adopted the prayer bead method to assess the effect of red noise on the derived parameters.

Results. We measured a secondary eclipse depth of 0.196%^{+ 0.071%}_−0.051%, which indicates a brightness temperature in the Ks band for the planet of 1885^{+ 212}_-168 K. We also measured a small deviation in the central phase of the secondary eclipse of −0.0079^{+ 0.0162}_-0.0043, which leads to a value for ecosω of −0.0123^{+ 0.0252}_-0.0067. However, this last result needs to be confirmed with more data.