Detection of multiple modes in a new double-mode RR Lyrae star

Context. We present the first long-time coverage of high precision and uninterrupted light curve of a new double-mode RR Lyrae star allowing the determination of accurate Fourier components and the estimatation of fundamental parameters. Aims. We used high-precision space data of a new star CoRoT ID 0101368812, obtained by the satellite CoRoT, towards an understanding of double-mode RR Lyrae stars and the stellar evolution & pulsation. Methods. The CoRoT data were corrected using jump and trend filtering codes and we applied the period-finding technique Period04. Results. Non-linearly coupled frequencies f0 = 2.049 d−1 (P0 = 0.488 d) and f1 = 2.750 d−1 (P1 = 0.364 d) are found up to the tenth order with a period ratio P1/P0 of 0.745 and an amplitude ratio A1/A0 of 2.705. The frequencies f0 and f1 are interpreted as radial modes. The first overtone is the dominant pulsation mode. A large number of 22 linear combinations of these modes are also detected. An unprecedented number of additional frequencies and their linear combinations, are detected in addition to the fundamental radial mode, the first overtone radial mode, and their linear combinations. The most surprising result is the unexpected period ratios 0.458, 0.285, and 0.217 of additional frequencies to fundamental radial mode, which imply a possible simultaneous excitation of fundamental, first, and third overtone radial modes, in addition to non-radial modes. Conclusions. The newly discovered CoRoT ID 0101368812 is the first member of a new class of RR Lyrae stars. These results give us an opportunity to test the theoretical models of mode saturation and growth in RR d pulsators.