Variability survey of brightest stars in selected OB associations⋆
1 Tartu Observatory, Observatooriumi 1, 61602 Tõravere, Estonia
2 Institute of Physics, University of Tartu, W. Ostwaldi Str 1, 50411 Tartu, Estonia
Received: 25 July 2016
Accepted: 21 October 2016
Context. The stellar evolution theory of massive stars remains uncalibrated with high-precision photometric observational data mainly due to a small number of luminous stars that are monitored from space. Automated all-sky surveys have revealed numerous variable stars but most of the luminous stars are often overexposed. Targeted campaigns can improve the time base of photometric data for those objects.
Aims. The aim of this investigation is to study the variability of luminous stars at different timescales in young open clusters and OB associations.
Methods. We monitored 22 open clusters and associations from 2011 to 2013 using a 0.25-m telescope. Variable stars were detected by comparing the overall light-curve scatter with measurement uncertainties. Variability was analysed by the light curve feature extraction tool FATS. Periods of pulsating stars were determined using the discrete Fourier transform code SigSpec. We then classified the variable stars based on their pulsation periods and available spectral information.
Results. We obtained light curves for more than 20 000 sources of which 354 were found to be variable. Amongst them we find 80 eclipsing binaries, 31 α Cyg, 13 β Cep, 62 Be, 16 slowly pulsating B, 7 Cepheid, 1 γ Doradus, 3 Wolf-Rayet and 63 late-type variable stars. Up to 55% of these stars are potential new discoveries as they are not present in the Variable Star Index (VSX) database. We find the cluster membership fraction for variable stars to be 13% with an upper limit of 35%.
Key words: stars: variables: general / stars: massive / surveys / open clusters and associations: general
Variable star catalogue (Tables A.1–A.10) and light curves are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (184.108.40.206) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/598/A108
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