Flavours of variability: 29 RR Lyrae stars observed with Kepler

Abstract

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.

Rotation, differential rotation, and gyrochronology of activeKeplerstars

“…To reduce the number of false positives, i.e., periodic variability not related to stellar rotation, we discarded 17 eclipsing binaries 2 , 878 planetary candidates 3 , 2 RR Lyrae stars Szabó et al 2010;Benkő et al 2010;Guggenberger et al 2012;Nemec et al 2011Nemec et al , 2013Moskalik et al 2012;Molnár et al 2012), and 84 γ Doradus and δ Scuti stars Ulusoy et al 2014;Balona et al 2011;Uytterhoeven et al 2011;Lampens et al 2013;Balona 2014). In total, 981 stars were discarded, leaving 23 143 targets, which are analyzed as described in the following section.…”

The additional-mode garden of RR Lyrae stars

“…In parallel, the first observations of the Kepler space telescope also revealed peaks in multiple stars at a a level of 1-10 mmag in the Fourier spectra [9]. These first detections are summarised in the Petersen diagram in figure 1.…”

The K2 RR Lyrae Survey

“…Molnár et al in these proceedings). 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].…”