Revisiting CoRoT RR Lyrae stars: detection of period doubling and temporal variation of additional frequencies^{⋆,⋆⋆,⋆⋆⋆,⋆⋆⋆⋆}

¹ Konkoly Observatory, MTA CSFK, Konkoly Thege Miklós út 15-17 1121 Budapest Hungary
e-mail: rszabo@konkoly.hu
² Laboratoire Lagrange, Université Nice Sophia-Antipolis, UMR 7293, Observatoire de la Côte d’Azur 06300, Nice, France
³ INAF − Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate ( LC), Italy
⁴ LESIA, Université Pierre et Marie Curie, Université Denis Diderot, Observatoire de Paris, 92195 Meudon Cedex, France
⁵ Institute of Astronomy, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
⁶ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge MA 02138, USA
⁷ Instituut voor Sterrenkunde, K.U. Leuven, Celestijnenlaan 200D, 3001 Heverlee, Belgium
⁸ Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
⁹ Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
¹⁰ Université de Toulouse, UPS-OMP, IRAP, Toulouse, France
¹¹ CNRS, IRAP, 14 avenue Edouard Belin, 31400 Toulouse, France

Received: 3 July 2014
Accepted: 1 August 2014

Abstract

Context. High-precision, space-based photometric missions like CoRoT and Kepler have revealed new and surprising phenomena in classical variable stars. Such discoveries were the period doubling in RR Lyrae stars and the frequent occurrence of additional periodicities some of which can be explained by radial overtone modes, but others are discordant with the radial eigenfrequency spectrum.

Aims. We search for signs of period doubling in CoRoT RR Lyrae stars. The occurrence of this dynamical effect in modulated RR Lyrae stars might help us to gain more information about the mysterious Blazhko effect. The temporal variability of the additional frequencies in representatives of all subtypes of RR Lyrae stars is also investigated.

Methods. We preprocess CoRoT light curves by applying trend and jump correction and outlier removal. Standard Fourier technique is used to analyze the frequency content of our targets and follow the time-dependent phenomena.

Results. The most comprehensive collection of CoRoT RR Lyrae stars, including new discoveries is presented and analyzed. We found alternating maxima and in some cases half-integer frequencies in four CoRoT Blazhko RR Lyrae stars, as clear signs of the presence of period doubling. This reinforces that period doubling is an important ingredient for understanding the Blazhko effect – a premise we derived previously from the Kepler RR Lyrae sample. As expected, period doubling is detectable only for short time intervals in most modulated RRab stars. Our results show that the temporal variability of the additional frequencies in all RR Lyrae subtypes is ubiquitous. The ephemeral nature and the highly variable amplitude of these variations suggest a complex underlying dynamics of and an intricate interplay between radial and possibly nonradial modes in RR Lyrae stars. The omnipresence of additional modes in all types of RR Lyrae – except in non-modulated RRab stars – implies that asteroseismology of these objects should be feasible in the near future.