OHP Preprint No. 99 : Metallic line doubling in RR Lyrae

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

A.B.Fokin1 and D.Gillet2

1 Institute for Astronomy of the Russian Academy of Sciences
  48 Pjatnitskaja, 109017 Moscow, Russia
2 Observatoire de Haute-Provence - CNRS F-04870 Saint-Michel l'Observatoire, France E-mail: gillet@obs-hp.fr

Astronomy & Astrophysics (in press)

A series of nonlinear nonadiabatic models for the variable star RR Lyrae are calculated and two Fe I and Fe II line profiles are reconstructed in order to modelise the recently confirmed line doubling phenomenon. We found the doubling phenomenon only in the Fe II line, while the Fe I line remains single all the time. The doubling is proved to be a result of a shock passage through the line formation region (LFR), in agreement with the Schwarzchild's mechanism (1952). Whether in the Fe II LFR the total shock amplitude in our models is already strong (about 40-60 km/s), in the Fe I LFR it is too faint to produce the line doubling. This means that actually in our models the shock developpement is too slow to achieve the high enough amplitude in the deep atmosphere where the Fe I line is formed. To confirm the observed Fe I doubling a more detailed model is required. In the contrary, in the Fe II LFR the associated shock wave undergoes a very rapid acceleration, which provokes a sudden appearance of the absorption component located near the zero velocity. Thus the shock that was first receding for the observer, becomes almost stationary during the doubling phenomenon before to be advancing. This three step scenario is well confirmed by recent high resolution observations, showing a similar complex doubling evolution of the line profile.

Keywords : Hydrodynamics - Shock waves - Stars: pulsation - Stars: variables: RR Lyrae - Stars: individual: RR Lyr

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