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

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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