Spectroscopic iron-to-hydrogen ratios, radial velocities, atmospheric parameters, and new photometric analyses are presented for 41 RR Lyrae stars (and one probable high-amplitude δ Sct star) located in the field-of-view of the Kepler space telescope. Thirty-seven of the RR Lyrae stars are fundamental-mode pulsators (i.e., RRab stars) of which 16 exhibit the Blazhko effect. Four of the stars are multiperiodic RRc pulsators oscillating primarily in the first-overtone mode. Spectroscopic [Fe/H] values for the 34 stars for which we were able to derive estimates range from −2.54 ± 0.13 (NR Lyr) to −0.05 ± 0.13 dex (V784 Cyg), and for the 19 Kepler-field non-Blazhko stars studied by Nemec et al. (2011) the abundances agree will with their photometric [Fe/H] values. Four non-Blazhko RR Lyrae stars that they identified as metal-rich (KIC 6100702, V2470 Cyg, V782 Cyg and V784 Cyg) are confirmed as such, and four additional stars (V839 Cyg, KIC 5520878, KIC 8832417, KIC 3868420) are also shown here to be metal-rich. Five of the non-Blazhko RRab stars are found to be more metalrich than [Fe/H]∼ −0.9 dex while all of the 16 Blazhko stars are more metal-poor than this value. New P -φ s 31 -[Fe/H] relationships are derived based on ∼970 days of quasi-continuous high-precison Q0-Q11 long-and short-cadence Kepler photometry. With the exception of some Blazhko stars, the spectroscopic and photometric [Fe/H] values are in good agreement. Several stars with unique photometric characteristics are identified, including a Blazhko variable with the smallest known amplitude and frequency modulations (V838 Cyg).

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The first detection of the period doubling phenomenon is reported in the Kepler RR Lyrae stars RR Lyr, V808 Cyg and V355 Lyr. Interestingly, all these pulsating stars show Blazhko modulation. The period doubling manifests itself as alternating maxima and minima of the pulsational cycles in the light curve, as well as through the appearance of half‐integer frequencies located halfway between the main pulsation period and its harmonics in the frequency spectrum. The effect was found to be stronger during certain phases of the modulation cycle. We were able to reproduce the period‐doubling bifurcation in our non‐linear RR Lyrae models computed by the Florida–Budapest hydrocode. This enabled us to trace the origin of this instability in RR Lyrae stars to a resonance, namely a 9:2 resonance between the fundamental mode and a high‐order (ninth) radial overtone showing strange‐mode characteristics. We discuss the connection of this new type of variation to the mysterious Blazhko effect and argue that it may give us fresh insights into solving this century‐old enigma.

We present the analysis of four first overtone RR Lyrae stars observed with the Kepler space telescope, based on data obtained over nearly 2.5 yr. All four stars are found to be multiperiodic. The strongest secondary mode with frequency f 2 has an amplitude of a few mmag, 20−45 times lower than the main radial mode with frequency f 1 . The two oscillations have a period ratio of P 2 /P 1 = 0.612 − 0.632 that cannot be reproduced by any two radial modes. Thus, the secondary mode is nonradial. Modes yielding similar period ratios have also recently been discovered in other variables of the RRc and RRd types. These objects form a homogenous group and constitute a new class of multimode RR Lyrae pulsators, analogous to a similar class of multimode classical Cepheids in the Magellanic Clouds. Because a secondary mode with P 2 /P 1 ∼ 0.61 is found in almost every RRc and RRd star observed from space, this form of multiperiodicity must be common. In all four Kepler RRc stars studied, we find subharmonics of f 2 at ∼ 1/2f 2 and at ∼ 3/2f 2 . This is a signature of period doubling of the secondary oscillation, and is the first detection of period doubling in RRc stars. The amplitudes and phases of f 2 and its subharmonics are variable on a timescale of 10 − 200 d. The dominant radial mode also shows variations on the same timescale, but with much smaller amplitude. In three Kepler RRc stars we detect additional periodicities, with amplitudes below 1 mmag, that must correspond to nonradial g-modes. Such modes never before have been observed in RR Lyrae variables.

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We present our analysis of Kepler observations of 29 RR Lyrae stars, based on 138 d of observation. We report precise pulsation periods for all stars. Nine of these stars had incorrect or unknown periods in the literature. 14 of the stars exhibit both amplitude and phase Blazhko modulations, with Blazhko periods ranging from 27.7 to more than 200 d. For V445 Lyr, a longer secondary variation is also observed in addition to its 53.2‐d Blazhko period. The unprecedented precision of the Kepler photometry has led to the discovery of the the smallest modulations detected so far. Moreover, additional frequencies beyond the well‐known harmonics and Blazhko multiplets have been found. These frequencies are located around the half‐integer multiples of the main pulsation frequency for at least three stars. In four stars, these frequencies are close to the first and/or second overtone modes. The amplitudes of these periodicities seem to vary over the Blazhko cycle. V350 Lyr, a non‐Blazhko star in our sample, is the first example of a double‐mode RR Lyrae star that pulsates in its fundamental and second overtone modes.

We present frequency analysis of RR Lyrae stars of globular cluster NGC 6362. 1 Observations and data analysis NGC 6362 is a nearby globular cluster of Oosterhoff I type. It has a mean metallicity of [Fe/H]= −0.95 and belongs to the old halo population ([1]). 35 RR Lyrae-type stars have been discovered in the cluster ([5]). We revisit these variables, taking advantage of the new CCD photometry accumulated by the Cluster AgeS Experiment (CASE). In our analysis we used 3200 V-band images collected with the 1-m Swope telescope of the Las Campanas Observatory between July 8th, 1999 and September 9th, 2009. The frequency analysis of the data was performed with the standard consecutive prewhitening technique. For full discussion of our results we refer the reader to [6]. 2 RR Lyrae variables of NGC 6362 16 RR Lyrae stars of NGC 6362 are fundamental mode pulsators (RRab variables) and 16 are first overtone pulsators (RRc variables). Two objects, previously identified as RRab stars, turned out to be double mode pulsators (RRd stars), with two lowest radial modes simultaneously excited. Finally, in V37 we detect two high-amplitude modes of close frequencies and with lightcurves significantly differing from those of RR Lyrae stars. The nature of V37 is a puzzle. It will not be discussed here. 2.1 Non-radial modes In 10 out of 16 RRc stars of NGC 6362 (63% of the sample) we detect a secondary short period variability, with the period ratio falling in the range of P x /P 1 = 0.60 − 0.65. The amplitudes of the secondary signals never exceed 6 mmag. Similar pulsators have recently been discovered in many stellar systems ([3], and references therein). Space observations indicate that this form of variability most likely occurs in almost all RRc and RRd stars ([4]). Detecting it in the ground-based data is difficult, however, because of the extremely low amplitude of the secondary periodicities. The incidence rate of 63%, that we report for NGC 6362, is the highest among all stellar systems observed

We present the first results of our analyses of selected RR Lyrae stars for which data have been obtained by the Kepler Mission. As expected, we find a significant fraction of the RRab stars to show the Blazhko effect, a still unexplained phenomenon that manifests itself as periodic amplitude and phase modulations of the light curve, on timescales of typically tens to hundreds of days. The long time span of the Kepler Mission of 3.5 yr and the unprecedentedly high precision of its data provide a unique opportunity for the study of RR Lyrae stars. Using data of a modulated star observed in the first roll as a showcase, we discuss the data, our analyses, findings, and their implications for our understanding of RR Lyrae stars and the Blazhko effect. With at least 40% of the RR Lyrae stars in our sample showing modulation, we confirm the high incidence rate that was only found in recent high-precision studies. Moreover, we report the occurrence of additional frequencies, beyond the main pulsation mode and its modulation components. Their half-integer ratio to the main frequency is reminiscent of a period doubling effect caused by resonances, observed for the first time in RR Lyrae stars.