First detection of period doubling in a bl herculis type star: Observations and theoretical models

Abstract

We report on the discovery of the first BL Herculis star displaying period-doubling behaviour as predicted by the hydrodynamic models of Buchler and Moskalik (ApJ 391:736, 1992). The star, with P0 = 2:4 d, is located in the Galactic bulge and was discovered with OGLE-III photometry. We present new nonlinear convective models, which, together with recent evolutionary tracks, put constraints on the stellar parameters. In particular, we estimate the mass and metallicity of the object.