CoRoT light curves of RR Lyrae stars^*,**

CoRoT 101128793: long–term changes in the Blazhko effect and excitation of additional modes

¹ INAF – Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate (LC), Italy e-mail: ennio.poretti@brera.inaf.it
² Konkoly Observatory of the Hungarian Academy of Sciences, PO Box 67, 1525 Budapest, Hungary
³ LAM, UMR 6110, CNRS/Univ. de Provence, 38 rue F. Joliot-Curie, 13388 Marseille, France
⁴ Observatoire de la Côte d'Azur, Université Nice Sophia-Antipolis, UMR 6525, Parc Valrose, 06108 Nice Cedex 02, France
⁵ Institute of Astronomy, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
⁶ Laboratoire d'Astrophysique de Toulouse-Tarbes, Université de Toulouse, CNRS, 14 Av. Édouard Belin, 31400 Toulouse, France
⁷ LESIA, Université Pierre et Marie Curie, Université Denis Diderot, Observatoire de Paris, 92195 Meudon Cedex, France
⁸ Dpt. de Inteligencia Artificial, UNED, Juan del Rosal 16, 28040 Madrid, Spain

Received: 5 May 2010
Accepted: 9 June 2010

Abstract

Context. The CoRoT (Convection, Rotation and planetary Transits) space mission provides a valuable opportunity to monitor stars with uninterrupted time sampling for up to 150 days at a time. The study of RR Lyrae stars, performed in the framework of the Additional Programmes belonging to the exoplanetary field, will particularly benefit from such dense, long-duration monitoring.

Aims. The Blazhko effect in RR Lyrae stars is a long-standing, unsolved problem of stellar astrophysics. We used the CoRoT data of the new RR Lyrae variable CoRoT 101128793 (f₀ = 2.119 d^-1, P = 0.4719296 d) to provide us with more detailed observational facts to understand the physical process behind the phenomenon.

Methods. The CoRoT data were corrected for one jump and the long-term drift. We applied different period-finding techniques to the corrected timeseries to investigate amplitude and phase modulation. We detected 79 frequencies in the light curve of CoRoT 101128793. They have been identified as the main frequency f₀  and its harmonics, two independent terms, the terms related to the Blazhko frequency f_m, and to several combination terms.

Results. A Blazhko frequency f_m = 0.056 d^-1 and a triplet structure around the fundamental radial mode and harmonics were detected, as were a long-term variability on the Blazhko modulation. Indeed, the amplitude of the main oscillation is decreasing along the CoRoT survey. The Blazhko modulation is one of the smallest observed in RR Lyrae stars. Moreover, the additional modes f₁ = 3.630  and f₂ = 3.159 d^-1 are detected. Taking its ratio with the fundamental radial mode into account, the term f₁ could be the identified as the second radial overtone. Detecting of these modes in horizontal branch stars is a new result obtained by CoRoT.