Searching for transits in the Wide Field Camera Transit Survey with difference-imaging light curves

¹ University Observatory Munich, Scheinerstrasse 1, 81679 München, Germany
e-mail: chicho@usm.uni-muenchen.de
² Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse 1, 85748 Garching, Germany
³ Leiden Observatory, Leiden University, Postbus 9513, 2300 RA Leiden, The Netherlands
⁴ Institute of Astronomy, Cambridge University, Madingley Road, Cambridge CB3 0HA, UK
⁵ University of Hertfordshire, Centre for Astrophysics Research, Science and Technology Research Institute, College Lane, AL10 9 AB Hatfield, UK
⁶ Depto. Astrofísica, Centro de Astrobiología (INTA-CSIC), ESAC campus, PO Box 78, 28691 Villanueva de la Cañada, Spain
⁷ Calar Alto Observatory, Centro Astronómico Hispano-Alemán, C/ Jesús Durbán Remón, 04004 Almería, Spain
⁸ Instituto Nacional de Astrofísica, Óptica y Electrónica, Luis Enrique Erro 1, Sta. Ma. Tonantzintla, 72840 Puebla, Mexico
⁹ Centro de Astrobiología (CSIC-INTA), Ctra. Ajalvir km. 4, 28850 Torrejón de Ardoz, Madrid, Spain

Received: 18 February 2013
Accepted: 2 October 2013

Abstract

The Wide Field Camera Transit Survey is a pioneer program aiming at for searching extra-solar planets in the near-infrared. The images from the survey are processed by a data reduction pipeline, which uses aperture photometry to construct the light curves. We produce an alternative set of light curves using the difference-imaging method for the most complete field in the survey and carry out a quantitative comparison between the photometric precision achieved with both methods. The results show that difference-photometry light curves present an important improvement for stars with J > 16. We report an implementation on the box-fitting transit detection algorithm, which performs a trapezoid-fit to the folded light curve, providing more accurate results than the box-fitting model. We describe and optimize a set of selection criteria to search for transit candidates, including the V-shape parameter calculated by our detection algorithm. The optimized selection criteria are applied to the aperture photometry and difference-imaging light curves, resulting in the automatic detection of the best 200 transit candidates from a sample of ~475 000 sources. We carry out a detailed analysis in the 18 best detections and classify them as transiting planet and eclipsing binary candidates. We present one planet candidate orbiting a late G-type star. No planet candidate around M-stars has been found, confirming the null detection hypothesis and upper limits on the occurrence rate of short-period giant planets around M-dwarfs presented in a prior study. We extend the search for transiting planets to stars with J ≤ 18, which enables us to set a stricter upper limit of 1.1%. Furthermore, we present the detection of five faint extremely-short period eclipsing binaries and three M-dwarf/M-dwarf binary candidates. The detections demonstrate the benefits of using the difference-imaging light curves, especially when going to fainter magnitudes.