Overtone and multi-mode RR Lyrae stars in the globular cluster M3

Jurcsik, Johanna and Smitola, Péter József and Hajdu, Gergely and Sódor, Ádám and Nuspl, János and Fűrész, Gábor and Moór, Attila and Kun, Emma and Pál, András and Bakos, Judit and Kelemen, János and Kovács, Tamás and Kriskovics, Levente and Sárneczky, Krisztián and Szalai, Tamás and Szing, Attila and Vida, Krisztián (2015) Overtone and multi-mode RR Lyrae stars in the globular cluster M3. ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 219 (2). ISSN 0067-0049

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Abstract

The overtone and multi-mode RR Lyrae stars in the globular cluster M3 are studied using a 200- d long, B, V and IC time-series photometry obtained in 2012. 70% of the 52 overtone variables observed show some kind of multi-periodicity (additional frequency at f0.61 = f1O/0.61 frequency ratio, Blazhko effect, double/multi-mode pulsation, period doubling). A signal at 0.587 frequency ratio to the fundamental-mode frequency is detected in the double-mode star, V13, which may be identified as the second radial overtone mode. If this mode-identification is correct, than V13 is the first RR Lyrae star showing triple-mode pulsation of the first three radial modes. Either the Blazhko effect or the f0.61 frequency (or both of these phenomena) appear in 7 double-mode stars. The P1O/PF period ratio of RRd stars showing the Blazhko effect are anomalous. A displacement of the main frequency component at the fundamental-mode with the value of modulation frequency (or its half) is detected in three Blazhko RRd stars parallel with the appearance of the overtone-mode pulsation. The f0.61 frequency appears in RRc stars that lie at the blue side of the double-mode region and in RRd stars, raising the suspicion that its occurrence may be connected to double-mode pulsation. The changes of the Blazhko and double-mode properties of the stars are also reviewed using the recent and archive photometric data.

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