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
Astronomy & Astrophysics (in press)
A series of nonlinear nonadiabatic models for the variable star RR Lyrae are
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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