Overtone and Multi-Mode Rr Lyrae Stars in the Globular Cluster M3

Abstract

The overtone and multi-mode RR Lyrae stars in the globular cluster M3 are studied using a 200 day long, B V , , and I C time-series photometry obtained in 2012. 70% of the 52 overtone variables observed show some kind of multi-periodicity (with additional frequency at f f 0.61 0.61 1O = frequency ratio, Blazhko effect, double/multi-mode pulsation, and period doubling). A signal at the 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 f 0.61 frequency (or both of these phenomena) appears in seven doublemode stars. The P P 1O F 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 that are parallel with the appearance of the overtone-mode pulsation. The f 0.61 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 doublemode properties of the stars are also reviewed using the recent and archive photometric data.

Anomalous double-mode RR Lyrae stars in the Magellanic Clouds

“…In addition, there is a group outside of this sequence with distinct features, like the presence of the Blazhko effect , peculiar light curve shape, or anomalous amplitude ratio. The same systematic differences show four anomalous RRd stars identified in the globular cluster M3 by Jurcsik et al (2014Jurcsik et al ( , 2015 (bottom right panel of Fig. 1).…”

“…In Fig. 1 we present Petersen diagrams for RRd stars in four environments: LMC, SMC (Soszyński et al 2016), Galactic bulge (Soszyński et al 2014), and globular cluster M3 (Jurcsik et al 2014(Jurcsik et al , 2015. Most of the RRd stars form a curved sequence continuing over a narrow range of period ratios 0.742 < P1O/PF < 0.748.…”

“…Petersen diagrams for RRd stars in four different stellar systems: LMC, SMC (Soszyński et al 2014), Galactic bulge (Soszyński et al 2014;Smolec et al 2015), and globular cluster M3 (Jurcsik et al 2014(Jurcsik et al , 2015. Small black dots mark the "classical" RRd stars, large yellow circles mark the anomalous RRd stars in the Magellanic Clouds or Blazhko RRd stars in the Galactic bulge and M3.…”

The Catalina Surveys Southern periodic variable star catalogue

“…Nevertheless, a small number of RRc's and a large fraction of RRd's have recently been found to exhibit the Blazhko effect (Wils, Kleidis & Broens 2008;Jurcsik et al 2014Jurcsik et al , 2015. It is also possible to confuse genuine such objects with those having incorrectly determined periods.…”

The K2 RR Lyrae Survey

“…Besides the half-integer frequencies due to period-doubling [12], extra frequencies have been found around the expected location of the second radial overtone frequency [13], around P X /P 1 = 0.61 [14], where P 1 and P X are the periods of first radial overtone and a presumably nonradial mode which seems to be ubiquitous in RRc and RRd stars [15]. In addition, anomalous first overtone / fundamental mode (P 1 /P 0 ) period ratios were uncovered [16], [17], [18], [19].…”