OHP Preprint No. 98 : Blazhko effect in RR Lyrae
The Blazhko effect on line profiles in the variable star RR Lyrae*
M.Chadid and D.Gillet
Observatoire de Haute-Provence (CNRS)
F-04870 Saint-Michel l'Observatoire, France
E-mail: chadid,gillet @obs-hp.fr
*Based on observations obtained at the Observatoire de
Haute-Provence (France).
Astronomy&Astrophysics : Received 8 June 1996 / Accepted 22 July 1996
Abstract
It is shown that the metallic line doubling phenomenon is well visible
when the Blazhko effect is maximum while only a line broadening takes place
when it is minimum. At this last phase, the hydrogen emission is very weak
(under the continuum) but its intensity increases progressively towards
the Blazhko maximum. The hydrogen line doubling does
not present a noticeable Blazhko phase variation. The wavelength position
of the metallic double line system attests that the ballistic motion of the
atmosphere has a weaker amplitude, when the Blazhko effect is minimum, than
at its maximum intensity. We detect a variation of the
-velocity deduced
from metallic absorption lines during
the Blazhko period but additional accurate observations are required
to determine its amplitude.
The acceleration of the shock wave, inducing line doubling phenomena, is
extremely large at all Blazhko phases (from a Mach number around 5 to 25)
between the metallic and hydrogen formation regions. Thus a high hypersonic
regime always exists in the high atmosphere of RR Lyr. These observational
results show that the radial pulsation is manifestly maximum at the maximum
Blazhko effect and its intensity is more and more reduced up to its minimum.
Finally it emerges that high quality line profiles, well
distributed over the Blazhko period, can provide some decisive tests to
determine the relevant mechanism at the origin of the Blazhko effect.
Keywords : Hydrodynamics --
Shock waves --
Magnetic field --
Stars: pulsation --
Stars: variables: RR Lyrae --
Stars: individual: RR Lyr
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