Rate and nature of false positives in the CoRoT exoplanet search^*

¹ Instituto de Astrofísica de Canarias, C/ Vía Láctea S/N, 38200 La Laguna (Spain) e-mail: [jmav;hdeeg]@iac.es
² School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK
³ Laboratoire d'Astrophysique de Marseille, UMR 6110 CNRS, Technopôle de Marseille-Étoile, 13388 Marseille Cedex 13, France
⁴ LESIA, UMR 8109 CNRS, Observatoire de Paris, UVSQ, Université Paris-Diderot, 5 place J. Janssen, 92195 Meudon, France
⁵ Institut d'Astrophysique Spatiale, UMR 8617 CNRS, Bât. 121, Université Paris-Sud, 91405 Orsay, France
⁶ Observatoire de Haute Provence, USR 2207 CNRS, OAMP, 04870 St. Michel l'Observatoire, France
⁷ School of Physics A28, University of Sydney, Australia
⁸ Institute of Planetary Research, DLR, Rutherfordstr. 2, 12489 Berlin, Germany
⁹ LUTH, UMR 8102 CNRS, Observatoire de Paris-Meudon, 5 place J. Janssen, 92195 Meudon, France
¹⁰ Rheinisches Institut für Umweltforschung, Universität zu Köln, Abt. Planetenforschung, Aachener Str. 209, 50931 Köln, Germany
¹¹ Research and Scientific Support Department, European Space Agency, ESTEC, 2200 Noordwijk, The Netherlands
¹² Observatório Nacional, Rio de Janeiro, RJ, Brazil
¹³ Institute for Astronomy, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
¹⁴ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
¹⁵ Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland
¹⁶ University of Liège, Allée du 6 août 17, Sart Tilman, Liège 1, Belgium
¹⁷ Observatoire de la Côte d'Azur, Laboratoire Cassiopée, CNRS UMR 6202, BP 4229, 06304 Nice Cedex 4, France
¹⁸ Institut d'Astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98bis Bd Arago, 75014 Paris, France
¹⁹ Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria
²⁰ School of Physics and Astronomy, R. and B. Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel
²¹ Center for Astronomy and Astrophysics, TU Berlin, Hardenbergstr. 36, 10623 Berlin, Germany
²² Dpto. de Astrofísica, Universidad de La Laguna, La Laguna, 38206 Tenerife, Spain
²³ Laboratoire d'Astronomie de Lille, Université de Lille 1, 1 impasse de l'Observatoire, 59000 Lille, France
²⁴ Institut de Mécanique Céleste et de Calcul des Ephémérides, UMR 8028 du CNRS, 77 avenue Denfert-Rochereau, 75014 Paris, France

Received: 23 February 2009
Accepted: 31 July 2009

Abstract

Context. The CoRoT satellite searches for planets by applying the transit method, monitoring up to 12 000 stars in the galactic plane for 150 days in each observing run. This search is contaminated by a large fraction of false positives, caused by different eclipsing binary configurations that might be confused with a transiting planet.

Aims. We evaluate the rates and nature of false positives in the CoRoT exoplanets search and compare our results with semiempirical predictions.

Methods. We consider the detected binary and planet candidates in the first three extended CoRoT runs, and classify the results of the follow-up observations completed to verify their planetary nature. We group the follow-up results into undiluted binaries, diluted binaries, and planets and compare their abundances with predictions from the literature.

Results. 83% of the initial detections are classified as false positives using only the CoRoT light-curves, the remaining 17% require follow-up observations. Finally, 12% of the candidates in the follow-up program are planets. The shape of the overall distribution of the false positive rate follows previous predictions, except for candidates with transit depths below about 0.4%. For candidates with transit depths in the range from 0.1–0.4%, CoRoT detections are nearly complete, and this difference from predictions is probably real and dominated by a lower than expected abundance of diluted eclipsing binaries.