M.Chadid and D.Gillet
Observatoire de Haute-Provence - CNRS
F-04870 Saint-Michel l'Observatoire, France
Received 9 August 1995 / Accepted 7 Septembre 1995
Abstract
For the first time, the observation of the line doubling
phenomenon over two metallic absorption lines of a RR Lyrae star (RR Lyr)
is reported. A resolving power of 42,000 and a time resolution close to 1% of
the pulsating period were necessary. Although a smaller exposure time would be
required to completely resolve this phenomenon over the whole spectrum,
we interpret it as the consequence of a "two-step" Schwarzschild's mechanism.
Thus a strong shock wave propagating throughout the photosphere around phase
0.93 would be at the origin of the observed line doubling. Because the
shock undergoes a sudden acceleration phase, a "jump" appears in the line
profile evolution. The shock is first receding and then almost stationary. Our
qualitative interpretation needs a theoretical confirmation with the help of a
nonlinear nonadiabatic pulsational model with an extended atmosphere taking
into account the presence of shock waves. Nevertheless it appears from our
observations that the dynamics of the atmosphere of RR Lyr is
important just above the photosphere and that strong shock exists at
this level because the doubling is already present in Fe I lines.
Keywords:
Hydrodynamics --
Shock waves --
Stars: pulsation --
Stars: individual: RR Lyr
*Based on observations obtained at the Observatoire de Haute-Provence ( France)