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Astron. Astrophys. 346, 487-490 (1999)

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1. Introduction

Pulsating variables are being continuously discovered in the course of large-scale projects. The Fourier decomposition describes their light curves in a powerful, synthetic way, supplying information on the pulsational content. As an example, Fourier parameters give the possibility to determine if a Cepheid pulsates in the fundamental or in an overtone mode (see Pardo & Poretti 1997 for an application to double-mode Cepheids) and this could make any Period-Luminosity relationship more clear.

The analysis of the light curve of short-period pulsating variables ([FORMULA]0.20 d) was carried out firstly by Antonello et al. (1986); then Poretti et al. (1990) and Musazzi et al. (1998) supplied new observational evidence. All these stars are located in the Galaxy and they do not belong to clusters; we shall call them hereinafter "galactic" variables. They are both Pop. I ([FORMULA] Sct stars) and Pop. II (SX Phe stars) objects; no clear separation of the light curves as a function of the population was detected.

The OGLE project collected a large amount of photometric data while monitoring the globular cluster NGC 5139[FORMULA] Cen (Kaluzny et al. 1996, 1997). 34 new SX Phe stars were discovered: 24 are presented by Kaluzny et al. (1996), 10 by Kaluzny et al. (1997). These data can supply original results since galactic stars do not display periods shorter than 0.06 d, while in the [FORMULA] Cen sample this value is rather an upper limit. Therefore, we have an opportunity to verify if there is a straight connection between the two different samples and, if any, to extend the period baseline.

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© European Southern Observatory (ESO) 1999

Online publication: May 21, 1999