Frequency analysis of the first-overtone RR Lyrae stars based on the Extended Aperture Photometry from the K2 data

Abstract

Additional low-amplitude signals are observed in many RR Lyrae stars, beside the pulsations in radial modes. The most common ones are short-period signals forming a period ratio of around 0.60--0.65 with the first overtone, or long-period signals forming a period ratio of around 0.68. The RR Lyrae stars may also exhibit quasi-periodic modulation of the light curves, known as the Blazhko effect. We used the extensive sample of the first-overtone RR Lyrae stars observed by the Kepler telescope during the K2 mission to search for and characterize these low-amplitude additional signals. K2 data provides space-based photometry for a statistically significant sample. Hence this data is excellent to study in detail pulsation properties of RR Lyrae stars. We used K2 space-based photometry for RR Lyrae candidates from Campaigns 0-19. We selected RR Lyrae stars pulsating in the first overtone and performed a frequency analysis for each star to characterize their frequency contents. We classified 452 stars as first-overtone RR Lyrae. From that sample, we selected 281 RR${}_{0.61}$ stars, 67 RR${}_{0.68}$ stars, and 68 Blazhko stars. We found particularly interesting stars which show all of the above phenomena simultaneously. We detected signals in RR${}_{0.61}$ stars that form period ratios lower than observed for the majority of stars. These signals likely form a new sequence in the Petersen diagram, around a period ratio of 0.60. In 32 stars we detected additional signals that form a period ratio close to that expected in RRd stars, but the classification of these stars as RRd is uncertain. We also report a discovery of additional signals in eight stars that form a new group in the Petersen diagram around the period ratio of 0.465-0.490. The nature of this periodicity remains unknown.

29 pages, 29 figures, 4 tables, accepted for publication in A&A, full tables are available upon request before publication

References in corpus (20)

• The K2 Mission: Characterization and Early results
• RR-Lyrae-type pulsations from a 0.26-solar-mass star in a binary system
• Kepler photometry of RRc stars: peculiar double-mode pulsations and period doubling
• Long time-scale behavior of the Blazhko effect from rectified Kepler data
• MOST photometry of the RRd Lyrae variable AQ Leo: Two radial modes, 32 combination frequencies, and beyond
• Revisiting CoRoT RR Lyrae stars: detection of period doubling and temporal variation of additional frequencies
• TESS observations of Cepheid stars: first light results
• An extensive photometric study of the Blazhko RR Lyrae star MW Lyr: I. Light curve solution
• First results on RR Lyrae stars with the TESS space telescope: untangling the connections between mode content, colors and distances
• Anomalous Double-Mode RR Lyrae Stars in the Magellanic Clouds
• Blazhko-type modulation in the double-mode RR Lyrae stars of the OGLE Galactic bulge collection
• Discovery of a new group of double-periodic RR Lyrae stars in the OGLE-IV photometry
• On the modulation of RR Lyrae stars in the globular cluster M3
• Peculiar double-periodic pulsation in RR Lyrae stars of the OGLE collection. I. Long-period stars with dominant radial fundamental mode
• Peculiar double-periodic pulsation in RR Lyrae stars of the OGLE collection. II. Short-period stars with dominant radial fundamental mode
• Asteroseismology of RR Lyrae stars with non-radial modes
• Frequency analysis of OGLE-IV photometry for classical Cepheids in Galactic fields: non-radial modes and modulations
• Automated Extended Aperture Photometry of K2 variable stars
• Spectroscopic and photometric time series of the bright RRc star T Sex
• The Changing Lightcurve of the Double-Mode RR Lyrae Variable Star V338 Boo

Cited by in corpus (7)

• To Grow Old and Peculiar: A Survey of Anomalous Variable Stars in M80 and Age Determination using K2 and Gaia
• The VELOCE Modulation Zoo I. Spectroscopic detection of non-radial modes in the first-overtone Cepheids BG Crucis, QZ Normae, V0391 Normae, and V0411 Lacertae
• On the incidence rate of RR Lyrae stars with non-radial modes
• Connections between the cycle-to-cycle light curve and O-C variations of the non-Blazhko RR Lyrae stars
• Exploring Low-Amplitude Variability in First Overtone Cepheids with TESS
• The VELOCE modulation zoo III. Detecting additional pulsation modes in optical spectra of classical Cepheids using semi-partial distance correlation periodograms
• Caught in the Act: Observations of the Double-mode RR Lyrae V338 Boo During the Disappearance of a Pulsation Mode