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Astron. Astrophys. 325, 1013-1024 (1997)

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Theoretical interpretation of the metallic line doubling phenonenon in the variable star RR Lyrae

A.B. Fokin 1 and D. Gillet 2

1 Institute for Astronomy of the Russia Academy of Sciences, 48 Pjatnitskaja, 109017 Moscow, Russia
2 Observatoire de Haute-Provence - CNRS, F-04870 Saint-Michel l'Observatoire, France

Received 4 October 1996 / Accepted 20 November 1996

Abstract

A series of nonlinear nonadiabatic models for the variable star RR Lyrae are calculated and Fe II and Ba II line profiles are reconstructed in order to study the recently detected line doubling phenomenon. We found the doubling in both absorption lines, which is proved to be a result of a shock passage through the line formation region (LFR), in agreement with the Schwarzschild (1952) mechanism. It is shown that a number of shock waves of different amplitudes and different physical origins form in the RR Lyrae atmosphere, but only the most strong one is responsible for the observed line doubling. In the Fe II and Ba II LFR, the associated shock undergoes a very rapid acceleration, which provokes a sudden appearance of a new absorption component near zero velocity. It is found that the shock is first receding for the observer, then becomes almost stationary during the doubling phenomenon, and then advances. These three phases of the shock evolution are well confirmed by recent high resolution observations (Chadid and Gillet 1996), showing a similar complex doubling evolution of the line profile.

Key words: hydrodynamics – shock waves – stars: oscillation – stars: variables – stars: individual: RR Lyr

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© European Southern Observatory (ESO) 1997

Online publication: April 28, 1998

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