The (non-)variability of magnetic chemically peculiar candidates in the Large Magellanic Cloud^⋆

¹ Department of Theoretical Physics and AstrophysicsMasaryk University, Kotlářská 2, 61137 Brno, Czech Republic
e-mail: epaunzen@physics.muni.cz
² Rozhen National Astronomical Observatory, Institute of Astronomy of the Bulgarian Academy of Sciences, PO Box 136, 4700 Smolyan, Bulgaria
³ Observatory and Planetarium of Johann Palisa, VŠB – Technical University, Ostrava, Czech Republic
⁴ Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
⁵ Department of Astronomy, Ohio State University, 140 W. 18th Ave., Columbus, OH 43210, USA
⁶ Institut für Astrophysik der Universität Wien, Türkenschanzstr. 17, 1180 Wien, Austria

Received: 23 August 2012
Accepted: 29 May 2013

Abstract

Context. The galactic magnetic chemically peculiar (mCP) stars of the upper main sequence are well known as periodic spectral and light variables. The observed variability is obviously caused by the uneven distribution of overabundant chemical elements on the surfaces of rigidly rotating stars. The mechanism causing the clustering of some chemical elements into disparate structures on mCP stars has not been fully understood up to now. The observations of light changes of mCP candidates recently revealed in the nearby Large Magellanic Cloud (LMC) should provide us with information about their rotational periods and about the distribution of optically active elements on mCP stars born in other galaxies.

Aims. We queried for photometry at the Optical Gravitational Lensing Experiment (OGLE)-III survey of published mCP candidates selected because of the presence of the characteristic λ5200 Å flux depression. In total, the intersection of both sources resulted in twelve stars. For these objects and two control stars, we searched for a periodic variability.

Methods. We performed our own and standard periodogram time series analyses of all available data. The final results are, amongst others, the frequency of the maximum peak and the bootstrap probability of its reality.

Results. We detected that only two mCP candidates, 190.1 1581 and 190.1 15527, may show some weak rotationally modulated light variations with periods of 1.23 and 0.49 days; however, the 49% and 32% probabilities of their reality are not very satisfying. The variability of the other 10 mCP candidates is too low to be detectable by their V and I OGLE photometry.

Conclusions. The relatively low amplitude variability of the studied LMC mCP candidates sample can be explained by the absence of photometric spots of overabundant optically active chemical elements. The unexpected LMC mCPs behaviour is probably caused by different conditions during the star formation in the LMC and the Galaxy.