Discovery of period doubling in BL Herculis stars of the OGLE survey. Observations and theoretical models

Details Discovery of period doubling in BL Herculis stars of the OGLE survey. Observations and theoretical models Discovery of period doubling in BL Herculis stars of the OGLE survey. Observations and theoretical models

2011-09-26

arxiv.org/abs/1109.5699v1

MNRAS, 419, 2407 (2012)

Astronomy and Astrophysics

Astrophysics

Solar and Stellar Astrophysics

18 pages, 18 figures, accepted for publication in MNRAS

Scientific paper

10.1111/j.1365-2966.2011.19891.x

We report the discovery of a period doubling behaviour in a 2.4d BL Herculis-type variable of the Galactic bulge. Another bulge BL Her-type star (P=2.25d) is a strong period doubling candidate. Both objects have been identified with the OGLE-III photometry. Possibility of period doubling in this type of pulsators has been predicted almost twenty years ago by Buchler & Moskalik. Our finding is the first observational confirmation of their theoretical results. Discovery of the first BL Herculis star showing the period doubling effect motivates a new theoretical investigation with the state-of-the-art convective pulsation codes. We present the results of initial model survey, specifically aimed at studying the observed period-doubled BL Her variable. All of our non-linear models have P=2.4d. The computations confirm that the period doubling effect is caused by the 3:2 resonance between the fundamental mode and the first overtone, as indicated by earlier radiative models of Buchler & Moskalik. Comparison of the computed and the observed light curves allows to constrain the parameters of the star, in particular its metallicity, which appears to be high, Z is approximately 0.01. The recent evolutionary tracks put also constraint on the mass of the star, which is close to M=0.50 solar masses.

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