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Astron. Astrophys. 352, 201-210 (1999)


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First detection of a frequency multiplet in the line-profile variations of RR Lyrae: towards an understanding of the Blazhko effect *

M. Chadid 1,2, K. Kolenberg **  3, C. Aerts  ***  3 and D. Gillet 4

1 European Southern Observatory (ESO), Alonso de Cordova 3107-P.O. 19001 Santiago, Chile (mchadid@eso.org)
2 Observatoire de la Côte d'Azur - CNRS (UMR 6528), Département A. Fresnel, B.P. 4229, 06304 Nice Cedex 4, France
3 Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200 B, 3001 Heverlee, Belgium (katrienk,conny@ster.kuleuven.ac.be)
4 Observatoire de Haute-Provence - CNRS, 04870 Saint-Michel l'Observatoire, France (gillet@obs-hp.fr)

Received 7 July 1999 / Accepted 5 October 1999

Abstract

All present models for explaining the Blazhko effect are based on the presence of non-radial components. Up to now, however, these components have not been found explicitly in the observational studies, which were all based on photoelectric data. We provide the first detection of a frequency multiplet in the line-profile variations of RR Lyrae. Performing a period analysis on 669 high resolution line profiles obtained with the spectrograph ELODIE at OHP, we clearly detect a multiplet structure, with a separation equal to the Blazhko frequency, around the main frequency and its harmonics. Additional observations are needed to decide about the existence of a quintuplet. The presence of the harmonics of the main frequency in the line profiles indicates the importance of non-linear effects in the pulsation.

The complete understanding of the origin of the Blazhko effect still needs further theoretical modelling and better new observations. Our detection of the frequency multiplet in the line-profile variations is a first essential step towards a decisive confrontation between the theoretical models and the observations.

Key words: stars: oscillations – stars: variables: RR Lyr – stars: individual: RR Lyr

* Based on observations obtained at the Observatoire de Haute-Provence, France
** Aspirant Fellow, Fund for Scientific Research, Flanders
*** Postdoctoral Fellow, Fund for Scientific Research, Flanders

© European Southern Observatory (ESO) 1999

Online publication: November 23, 1999

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