High angular resolution imaging and infrared spectroscopy of CoRoT candidates^⋆,⋆⋆

¹ Thüringer Landessternwarte Tautenburg, 07778 Tautenburg, Germany
e-mail: guenther@tls-tautenburg.de
² Observatoire de l’Université de Genève, 51 chemin des Maillettes, 1290 Sauverny, Switzerland
³ Research and Scientific Support Department, ESTEC/ESA, PO Box 299, 2200 AG Noordwijk, The Netherlands
⁴ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
⁵ Dpto. de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
⁶ Laboratoire d’Astrophysique de Marseille, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
⁷ McDonald Observatory, The University of Texas at Austin, Austin, TX 78712, USA
⁸ University of Liège, Allée du 6 août 17, S. Tilman, Liège 1, Belgium
⁹ Georg-August-Universität, Institut für Astrophysik, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
¹⁰ Observatoire de la Côte d’Azur, Laboratoire Cassiopée, BP 4229, 06304 Nice Cedex 4, France
¹¹ Institut d’Astrophysique Spatiale, Université Paris-Sud 11, 91405 Orsay, France
¹² LESIA, UMR 8109 CNRS, Observatoire de Paris, UVSQ, Université Paris-Diderot, 5 place J. Janssen, 92195 Meudon, France
¹³ LUTH, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92195 Meudon, France
¹⁴ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
¹⁵ Department of Physics and Astronomy, Ny Munkegade 120 University of Aarhus, 8000 Aarhus C, Denmark

Received: 13 December 2012
Accepted: 20 June 2013

Abstract

Context. Studies of transiting extrasolar planets are of key importance for understanding the nature of planets outside our solar system because their masses, diameters, and bulk densities can be measured. An important part of transit-search programmes is the removal of false-positives. In the case of the CoRoT space mission, the majority of the false-positives are removed by a detailed analysis of the light curves and by seeing-limited imaging in- and out-of-transit. However, the critical question is how many of the candidates that passed all these tests are false-positives. Such false-positives can be caused by eclipsing binaries, which are either related or unrelated to the targets.

Aims. For our study we selected 25 CoRoT candidates that have already been screened against false-positives using detailed analysis of the light curves and seeing-limited imaging, which has transits that are between 0.7 and 0.05% deep. Our aim is to search for companion candidates that had not been recognized in previous observations.

Methods. We observed 20 candidates with the adaptive optics imager NaCo and 18 with the high-resolution infrared spectrograph CRIRES.

Results. We found previously unknown stars within 2′′ of the targets in seven of the candidates. All of these are too faint and too close to the targets to have been previously detected with seeing-limited telescopes in the optical. Our study thus leads to the surprising results that if we remove all candidates excluded by the sophisticated analysis of the light-curve, as well as carrying out deep imaging with seeing-limited telescopes, still 28−35% of the remaining candidates are found to possess companions that are bright enough to be false-positives.

Conclusions. Given that the companion candidates cluster around the targets and that the J − K colours are consistent with physical companions, we conclude that the companion candidates are more likely to be physical companions rather than unrelated field stars.