Binary Evolution Pulsator (BEP)

New type of RR Lyrae-like variable identified in a binary system.

RR-Lyrae-type pulsations from a 0.26-solar-mass star in a binary system

G. Pietrzyński, I. Thompson, W. Gieren, D. Graczyk, K. Stępień, G. Bono, P. Moroni, B. Pilecki, A. Udalski, I. Soszyński, G. Preston, N. Nardetto, A. McWilliam, I. Roederer, M. Górski, P. Konorski, J. Storm

2012, Nature, 484, 75

Artist version of the mass transfer in a binary system

Binary Evolution Pulsators (BEPs) refer to the systems which, after the episode of mass transfer, consist of a low-mass pulsating component and its companion. The first of its kind, OGLE-BLG-RRLYR-02792, is a binary with RR Lyrae-like pulsator of mass of 0.26 M, and evolved from close binary system with an initial orbital period of 2.9 days. BEP is a very short-lived phase where the physical properties of the pulsator happen to place it in the same instability strip of the Hertzsprung-Russell diagram as that occupied by classical pulsators. Estimations show that 0.2% of RR Lyrae stars may be contaminated by BEPs, which implies that distances measured with RR Lyrae stars should not be significantly affected by these binary interlopers.

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