EPIC 201585823, a rare triple-mode RR Lyrae star discovered in K2 mission data

Abstract

We have discovered a new, rare triple-mode RR Lyr star, EPIC 201585823, in the Kepler K2 mission Campaign 1 data. This star pulsates primarily in the fundamental and first-overtone radial modes, and, in addition, a third nonradial mode. The ratio of the period of the nonradial mode to that of the first-overtone radial mode, 0.616285, is remarkably similar to that seen in 11 other triple-mode RR Lyr stars, and in 260 RRc stars observed in the Galactic Bulge. This systematic character promises new constraints on RR Lyr star models. We detected subharmonics of the nonradial mode frequency, which are a signature of period doubling of this oscillation; we note that this phenomenon is ubiquitous in RRc and RRd stars observed from space, and from ground with sufficient precision. The nonradial mode and subharmonic frequencies are not constant in frequency or in amplitude. The amplitude spectrum of EPIC 201585823 is dominated by many combination frequencies among the three interacting pulsation mode frequencies. Inspection of the phase relationships of the combination frequencies in a phasor plot explains the `upward' shape of the light curve. We also found that raw data with custom masks encompassing all pixels with significant signal for the star, but without correction for pointing changes, is best for frequency analysis of this star, and, by implication, other RR Lyr stars observed by the K2 mission. We compare several pipeline reductions of the K2 mission data for this star.

Accepted for publication in MNRAS

References in corpus (15)

• The K2 Mission: Characterization and Early results
• A Technique for Extracting Highly Precise Photometry for the Two-Wheeled Kepler Mission
• A unifying explanation of complex frequency spectra of gamma Dor, SPB and Be stars: combination frequencies and highly non-sinusoidal light curves
• Automated preparation of Kepler time series of planet hosts for asteroseismic analysis
• K2P${}^2$ $-$ A photometry pipeline for the K2 mission
• K2 Variable Catalogue: Variable Stars and Eclipsing Binaries in K2 Campaigns 1 and 0
• Kepler photometry of RRc stars: peculiar double-mode pulsations and period doubling
• 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
• Pulsational Frequency and Amplitude Modulation in the $\delta$\,Sct star KIC\,7106205
• Blazhko-type modulation in the double-mode RR Lyrae stars of the OGLE Galactic bulge collection
• Double-mode radial-non-radial RR Lyrae stars in the OGLE photometry of the Galactic bulge
• Double mode RR Lyrae stars in Omega Centauri
• Multi-Periodic Oscillations in Cepheids and RR Lyrae-Type Stars
• Intriguing triple-mode RR Lyrae star with period doubling

Cited by in corpus (20)

• The K2 Ecliptic Plane Input Catalog (EPIC) and Stellar Classifications of 138,600 Targets in Campaigns 1-8
• Standard Galactic Field RR Lyrae. I. Optical to Mid-infrared Phased Photometry
• K2 space photometry reveals rotational modulation and stellar pulsations in chemically peculiar A and B stars
• 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
• The census of non-radial pulsation in first-overtone RR Lyrae stars of the OGLE Galactic bulge collection
• Non-radial pulsation in first overtone Cepheids of the Small Magellanic Cloud
• Extended Aperture Photometry of K2 RR Lyrae stars
• Unveiling the Intricate Symphony of Nonlinear Pulsation Mode Interactions in High-Amplitude $\delta$ Scuti Stars
• Frequency analysis of the first-overtone RR Lyrae stars based on the Extended Aperture Photometry from the K2 data
• Time series analysis of bright TESS RRc stars: Additional modes, phase variations and more
• Investigation of the Nature of the B[e] Star CI Cam in the Optical Range
• Four 'Peculiar' RRd Stars Observed by K2
• Uncorrelated Amplitude and Frequency Variations of the Harmonics in SX Phoenicis Star XX Cygni
• K2P${}^2$: Reduced data from campaigns 0-4 of the K2 mission
• Exploring the unexpected: Disharmonized harmonic pulsation modes in high-amplitude $\delta$ Scuti stars
• Asteroseismology
• Big Signals, Small Signals, Systematics
• The first decade of RR Lyrae space photometric observations
• Harmonics as a Hidden Window into the Turbulent Convective Envelope of non-Blazhko RRab Stars