First Overtone RR Lyrae Stars in the OGLE Collection

First Overtone RR Lyrae Stars in the OGLE Collection

Henryka Netzel, Radosław Smolec and Igor Soszyński

We present the preliminary results of the analysis of the Optical Gravitational Lensing Experiment (OGLE) data for the first overtone RR Lyrae stars (RRc) from the Galactic bulge. In the OGLE collection of variable stars, there are more than 10 000 RRc stars with six seasons of observations available. We analyzed this sample in order to detect non-radial modes and to study the Blazhko phenomenon, which is a quasi-periodic modulation of amplitude and/or phase.
We found new members of the group in which, besides the first overtone, there is another short-period signal, forming a characteristic period ratio of around 0.61 with the first overtone period. Previous analysis of the selected stars from the OGLE collection resulted in a discovery of more than 200 stars. After our analysis of all the RRc stars observed by OGLE, the number of known such stars exceeds 700.
In the previous analysis of the selected RRc stars, we discovered an entirely new double-periodic group in which, besides the first overtone, there is another signal. It has a period longer than the period of the first overtone, and forms a characteristic period ratio around 0.68. Before the present study, this group consisted of 19 stars found in the OGLE data and one star found in the Kepler data. The analysis of the whole sample of RRc stars resulted in a discovery of almost 70 new members of this group.
Additionally, in several stars with non-radial modes, we detected the Blazhko phenomenon.

Proceedings of the Polish Astronomical Society, vol. 6, 157-161 (2018)

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