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Post Info TOPIC: OGLE-BLG-RRLYR-02792
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RE: OGLE-BLG-RRLYR-02792
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Title: Pulsation models for the 0.26M_sun star mimicking RR Lyrae pulsator. Model survey for the new class of variable stars
Authors: R. Smolec, G. Pietrzynski, D. Graczyk, B. Pilecki, W. Gieren, I. Thompson, K. Stepien, P. Karczmarek, P. Konorski, M. Gorski, K. Suchomska, G. Bono, P.G. Prada Moroni, N. Nardetto

We present non-linear hydrodynamic pulsation models for OGLE-BLG-RRLYR-02792 - a 0.26 solar mass pulsator, component of the eclipsing binary system, analysed recently by Pietrzynski et al. The star's light and radial velocity curves mimic that of classical RR Lyrae stars, except for the bump in the middle of the ascending branch of the radial velocity curve. We show that the bump is caused by the 2:1 resonance between the fundamental mode and the second overtone - the same mechanism that causes the Hertzsprung bump progression in classical Cepheids. The models allow to constrain the parameters of the star, in particular to estimate its absolute luminosity (approx 33L_sun) and effective temperature (approx 6970K, close to the blue edge of the instability strip).
We conduct a model survey for the new class of low mass pulsators similar to OGLE-BLG-RRLYR-02792 - products of evolution in the binary systems. We compute a grid of models with masses corresponding to half (and less) of the typical mass of RR Lyrae variable, 0.20 solar masses<=M<=0.30 solar masses, and discuss the properties of the resulting light and radial velocity curves. Resonant bump progression is clear and may be used to distinguish such stars from classical RR Lyrae stars. We present the Fourier decomposition parameters for the modelled light and radial velocity curves. The expected values of the phi_31 Fourier phase for the light curves differ significantly from that observed in RR Lyrae stars, which is another discriminant of the new class.

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Blobrana


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Posts: 131433
Date:
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Title: RR-Lyrae-type pulsations from a 0.26-solar-mass star in a binary system
Authors: G. Pietrzynski, I. B. Thompson, W. Gieren, D. Graczyk, K. Stepien, G. Bono, P. G. Prada Moroni, B. Pilecki, A. Udalski, I. Soszynski, G. Preston, N. Nardetto, A. McWilliam, I. Roederer, M. Gorski, P. Konorski, J. Storm

RR Lyrae pulsating stars have been extensively used as tracers of old stellar populations for the purpose of determining the ages of galaxies, and as tools to measure distances to nearby galaxies. There was accordingly considerable interest when the RR Lyr star OGLE-BLG-RRLYR-02792 was found to be a member in an eclipsing binary system, as the mass of the pulsator (hitherto constrained only by models) could be unambiguously determined. Here we report that RRLYR-02792 has a mass of 0.26 solar masses and therefore cannot be a classical RR Lyrae star. Through models we find that its properties are best explained by the evolution of a close binary system that started with 1.4 solar masses and 0.8 solar masses stars orbiting each other with an initial period of 2.9 days. Mass exchange over 5.4 Gyr produced the observed system, which is now in a very short-lived phase where the physical properties of the pulsator happen to place it in the same instability strip of the H-R diagram occupied by RR Lyrae stars. We estimate that samples of RR Lyr stars may contain a 0.2 percent contamination with systems similar to this one, implying that distances measured with RR Lyrae stars should not be significantly affected by these binary interlopers.

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