Abstract
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. We pre-process 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. 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 to understand 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 sub-types 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 (Abridged).
Highlights
The advent of space photometry has opened up new vistas in investigating stellar pulsations and oscillations
Our results show that the temporal variability of the additional frequencies in all RR Lyrae subtypes is ubiquitous
The sample consists of all RR Lyrae subtypes: Blazhko and unmodulated RRab stars, two RRc, and one RRd star
Summary
We applied standard packages, such as MuFrAn (Kolláth 1990) and Period (Lenz & Breger 2005), to perform Fourier analysis.3.1. There is no obvious, strongly alternating pattern in the CoRoT RR Lyrae maxima that could have triggered a thorough analysis earlier, though in some cases a detailed inspection does show period doubling persisting through a few pulsational cycles as we show later in this work. CoRoT light curves are shorter than the Kepler ones and have lower precision at the same apparent brightness. Since period doubling is usually only temporarily noticeable in the light curves (but see Le Borgne et al 2014), we do not expect to see PD signs in both the light curve and the frequency spectrum in each case. In this work we investigate both the Fourier spectrum between the dominant mode and its harmonics, aiming at finding HIFs at exactly between two consecutive harmonics and the light curves themselves, looking for suspicious alternating pattern. We report tentative detection in those cases where PD is present in either or both domains
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