CoRoT light curves of RR Lyrae stars - CoRoT 101128793: long–term changes in the Blazhko effect and excitation of additional modes

摘要

Context. The CoRoT (Convection, Rotation and planetaryTransits) space mission provides a valuable opportunity to monitorstars with uninterrupted time sampling for up to 150 days at a time.The study of RR Lyrae stars, performed in the framework of theAdditional Programmes belonging to the exoplanetary field, willparticularly 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 thenew RR Lyrae variable CoRoT 101128793 (f0=2.119d-1, P=0.4719296d) to provide us with more detailedobservational facts to understand the physical process behind thephenomenon. Methods. The CoRoT data were corrected for one jump and thelong-term drift. We applied different period-finding techniques to thecorrected timeseries to investigate amplitude and phase modulation. Wedetected 79 frequencies in the light curve of CoRoT 101128793. Theyhave been identified as the main frequency f0 and its harmonics, two independent terms, the terms related to the Blazhko frequency fm, and to several combination terms. Results. A Blazhko frequency fm=0.056d-1anda triplet structure around the fundamental radial mode and harmonicswere detected, as were a long-term variability on the Blazhkomodulation. Indeed, the amplitude of the main oscillation is decreasingalong the CoRoT survey. The Blazhko modulation is one of the smallestobserved in RR Lyrae stars. Moreover, the additional modes =3.630 and f2=3.159d-1are detected. Taking its ratio with the fundamental radial mode into account, the term could be the identified as the second radial overtone. Detecting ofthese modes in horizontal branch stars is a new result obtained byCoRoT. Key words: stars: variables: RR Lyrae- stars: oscillations- stars: interiors - stars: individual: CoRoT 101128793 - techniques: photometric