KIC 2831097 - a 2-yr-orbital-period RR Lyrae binary candidate

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 traveltime 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 ≈2 yr is the shortest among the non-eclipsing RR Lyrae binary candidates. The binary model gives the lowest estimate for the mass of the companion of 8.4 M_⊙, 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.