Ground-based photometry of space-based transit detections: photometric follow-up of the CoRoT  mission ^*

¹ Instituto de Astrofísica de Canarias, C. via Lactea S/N, 38205 La Laguna, Tenerife, Spain e-mail: hdeeg@iac.es
² Observatoire de Genève, Université de Genève, 51 chemin des Maillettes, 1290 Sauverny, Switzerland
³ Institut d'Astrophysique et de Géophysique, Université de Liège, 4000 Liège, Belgium
⁴ School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel
⁵ LESIA, Observatoire de Paris-Meudon, 5 place Jules Janssen, 92195 Meudon, France
⁶ Thüringer Landessternwarte, Sternwarte 5, Tautenburg 5, 07778 Tautenburg, Germany
⁷ School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK
⁸ Laboratoire d'Astrophysique de Marseille, 38, rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
⁹ Institut d'Astrophysique de Paris, Université Pierre & Marie Curie, 98bis Bd Arago, 75014 Paris, France
¹⁰ Institute of Planetary Research, DLR, Rutherfordstr. 2, 12489 Berlin, Germany
¹¹ Research and Scientific Support Department, ESTEC/ESA, 2200 Noordwijk, The Netherlands
¹² Institute of Astronomy, University of Vienna, Türkenschanzstr. 17, 1180 Vienna, Austria
¹³ Center for Astronomy and Astrophysics, TU Berlin, Hardenbergstr. 36, 10623 Berlin, Germany

Received: 9 March 2009
Accepted: 9 July 2009

Abstract

The motivation, techniques and performance of the ground-based photometric follow-up of transit detections by the CoRoT space mission are presented. Its principal raison d'être arises from the much higher spatial resolution of common ground-based telescopes in comparison to CoRoT's cameras. This allows the identification of many transit candidates as arising from eclipsing binaries that are contaminating CoRoT's lightcurves, even in low-amplitude transit events that cannot be detected with ground-based obervations. For the ground observations, “on” – “off” photometry is now largely employed, in which only a short timeseries during a transit and a section outside a transit is observed and compared photometrically. CoRoTplanet candidates' transits are being observed by a dedicated team with access to telescopes with sizes ranging from 0.2 to 2 m. As an example, the process that led to the rejection of contaminating eclipsing binaries near the host star of the Super-Earth planet CoRoT-7b is shown. Experiences and techniques from this work may also be useful for other transit-detection experiments, when the discovery instrument obtains data with a relatively low angular resolution.