| Abstract
| - Abstract. A detailed light-curve analysis is presented for a first-overtone RR Lyrae star, MACHO* J050918.712−695015.31, based on MACHO and OGLE-III observations. As a foreground object of the Large Magellanic Cloud, it gives an extraordinary opportunity to study an almost continuous, 12-yr long data set of a relatively bright (V≈ 15.0 mag) RRc star with rapid period change. Cyclic period modulation is suggested by the O-C method, where the cycle length is about 8 yr. With the available unique data set, we could draw strong limits on other light-curve changes that may be associated with the period modulation. We could exclude both multiple periodicity and amplitude modulation unambiguously. Any theoretical model should reproduce the observed lack of photometric modulations. Simple arguments are also given for possible hydromagnetic effects.
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