KIC 2831097 - A 2-year orbital-period RR Lyrae binary candidate

TL;DR

This paper reports the discovery of a potential binary system involving an RR Lyrae star with a 2-year orbit, possibly hosting a black hole companion, based on Kepler data showing light travel-time effects and pulsation variations.

Contribution

The study presents the first evidence of a non-eclipsing RR Lyrae binary candidate with a short orbital period and a potential black hole companion, using Kepler observations.

Findings

Detected light travel-time effect indicating binary motion.

Estimated companion mass suggests a black hole candidate.

Observed non-radial pulsations and Blazhko-like modulation.

Abstract

We report the discovery of a new Kepler first-overtone RR Lyrae pulsator, KIC 2831097. The pulsation shows large, 0.1 d amplitude, systematic phase variations that can be interpreted as light travel-time effect caused by orbital motion in a binary system, superimposed on a linear pulsation-period decrease. The assumed eccentric (e=0.47) orbit with the period of approximately 2 yr is the shortest among the non-eclipsing RR Lyrae binary candidates. The binary model gives a lowest estimate for the mass of the companion of 8.4 M_Sun, that places it among black hole candidates. Beside the first-overtone pulsation, numerous additional non-radial pulsation frequencies were also identified. We detected an ~47-d Blazhko-like irregular light-curve modulation.