A photometric long-term study of chemically peculiar stars in open clusters⋆
Institut für Astronomie der Universität Wien,
2 Royal Observatory of Belgium, Ringlaan 3, Brussels, Belgium
3 Hvar Observatory, Faculty of Geodesy, University of Zagreb, Kačićeva 26, 10000 Zagreb, Croatia
4 INAF - Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
5 Department of Physics and Astronomy, The Open University, Milton Keynes, MK7 6AA, UK
6 Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden
Accepted: 11 September 2010
Context. Photometric variability of chemically peculiar (CP) stars of the upper main sequence is closely connected to their local stellar magnetic field and their rotational period. Long term investigations, as presented here, help us to identify possible stellar cycles (as in the Sun). Furthermore, these data provide a basis for detailed surface mapping techniques.
Aims. Photoelectric Strömgren uvby time series for 27 CP stars within the boundaries of open clusters are presented. In addition, Hipparcos photometric data (from 1989 to 1993) are used for our analysis. Our observations cover a time period of about six years (1986 to 1992) with typically fifteen measurements for each objects. These observations help us to determine the rotational periods of these objects.
Methods. A standard reduction procedure was applied to the data. When possible, we merged our data sets with already published ones to obtain a more significant result. A detailed time series analysis was performed, involving five different methods to minimize spurious detections.
Results. We established, for the first time, variability for fourteen CP stars. For additional two stars, a merging of already published data sets, resulted in more precise periods, whereas for six objects, the published periods could be confirmed. Last, but not least, no significant variations were found for five stars. Apart from six stars, all targets seem to be members of their host open clusters.
Conclusions. The present observations fill an important gap in previous photometric long-time studies of CP stars. The presented open cluster members are excellent targets for follow-up observations, employing for example polarimetric, high-resolution spectroscopic, and surface mapping techniques.
Key words: stars: chemically peculiar / open clusters and associations: general / stars: variables: general
All photometric measurements are available in electronic form 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/525/A16
© ESO, 2010