Long-term photometric monitoring with the Mercator telescope^*,**

Frequencies and multicolour amplitudes of γ Doradus stars

¹ Koninklijke Sterrenwacht van België, Ringlaan 3, 1180 Brussel, Belgium e-mail: Jan.Cuypers@oma.be
² Instituut voor Sterrenkunde, K.U.Leuven, Celestijnenlaan 200 D, 3001 Leuven, Belgium
³ Department of Astrophysics, Radboud University Nijmegen, 6500 GL Nijmegen, The Netherlands
⁴ Oxford Astrophysics, University of Oxford, Oxford, OX1 3RH, UK
⁵  Telescope, Calle Alvarez de Abreu 70, 38700 Santa Cruz de La Palma, Spain
⁶ Service d'Astrophysique, IRFU/DSM/CEA Saclay, L'Orme des Merisiers, 91191 Gif-sur-Yvette Cedex, France
⁷ Jet Propulsion Laboratory, 4800 Oak Grove Drive M/S: 183-900, Pasadena, CA 91109, USA
⁸ Belgisch Instituut voor Ruimte-Aëronomie, Ringlaan 3, 1180, Brussel, Belgium
⁹ Institut für Astronomie, Universität Wien, Türkenschanzstrasse 17, 1180 Wien, Austria
¹⁰ Koninklijk Meteorologisch Instituut, Ringlaan 3, 1180 Brussel, Belgium

Received: 20 January 2009
Accepted: 5 March 2009

Abstract

Context. γ Dor stars are excellent targets for asteroseismology since the gravity modes present in these stars probe the deep stellar interiors. Mode identification will improve the knowledge of these stars considerably.

Aims. A selected group of γ Dor stars and some candidates were observed with the Mercator telescope to find and/or confirm the periodicities in the light variations and to derive reliable amplitude ratios in different pass bands.

Methods. A frequency analysis was performed on all new data obtained in the Geneva photometric system. In order to have more reliable and accurate frequencies, the new data were combined with similar data from the literature and with Hipparcos observations. A set of frequencies that minimized the residuals in a harmonic fit was searched for while allowing means and amplitudes to vary from one observation set to another.

Results. Frequencies and amplitudes in the photometric passbands of the Geneva system are given for 21 γ Dor stars. We report the discovery of HD 74504 as a newly found γ Dor star.

Conclusions. Our study provides the first extensive multicolour database for the understanding of gravity modes in F-type stars.