EDP Sciences
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Volume 398, Number 1, January IV 2003
Page(s) 213 - 222
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20021595

A&A 398, 213-222 (2003)
DOI: 10.1051/0004-6361:20021595

Fourier decomposition and frequency analysis of the pulsating stars with P < 1 d in the OGLE database

II. Multiperiodic RR Lyrae variables in the Galactic Bulge
P. Moskalik1 and E. Poretti2

1  Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warsaw, Poland
2  INAF-Osservatorio Astronomico di Brera, Via Bianchi 46, 23807 Merate, Italy

(Received 10 September 2002 / Accepted 30 October 2002)

We present the results of a systematic search for multiperiodic pulsators among the Galactic Bulge RR Lyrae stars of the OGLE-1 sample. We identify one "canonical" double-mode variable (RRd star) pulsating in two radial modes. In 38 stars we detect secondary periodicities very close to the primary pulsation frequency. This type of multiperiodic variables constitute ~23% of RRab and ~5% of RRc population of the Bulge. With the observed period ratios of 0.95-1.02 the secondary periods must correspond to nonradial modes of oscillation. Their beating with the primary (radial) pulsation leads to a long-term amplitude and phase modulation, known as the Blazhko effect. The Blazhko RRab variables occur more frequently in the Galactic Bulge than in the LMC. The opposite tendency is seen in case of the RRd stars. The differences of incidence rates are most likely caused by different metallicity of the two populations. We discuss pulsation properties of the OGLE-1 Blazhko stars and compare them with predictions of theoretical models. We argue, that the oblique magnetic pulsator model of Shibahashi (2000) cannot account for the observations and should be ruled out.

Key words: stars: horizontal branch -- stars: oscillations -- stars: variables: RR Lyr

Offprint request: P. Moskalik, pam@camk.edu.pl

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