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Chemically peculiar stars

Extragalactic CP stars

The first extragalactic classical chemically peculiar stars more than 100 years after the discovery of this group were detected (Maitzen et al. 2001). Using the tool of CCD a-photometry, eight definite positive detections in the globular-like stellar cluster NGC 1866 and its surrounding in the Large Magellanic Cloud were made (Figure). More than 1950 objects down to 20.5 mag were observed. Furthermore we found three objects with significantly negative a-values indicating either an Ae/shell or lBootis nature. The overall percentage of chemically peculiar stars for NGC 1866 (1.5 %) seems lower than for the majority of open clusters in our Milky Way whereas the incidence within the LMC field is decisively less (0.3 %).

Article in the University newspaper (in German)

To corroborate the result of a search for chemically peculiar stars in the Large Magellanic Cloud (LMC), we present measurements obtained from CCD imaging of two fields, one containing a young open cluster (NGC 1711). While for the latter field, including its surrounding we obtain a contribution of 3% of chemically peculiar stars detectable by a photometry, the second field yields about half of this value in good accordance with the finding for NGC 1866. Thus, we are faced with the fact that our incipient impression about a substantially lower appearance of magnetic chemically peculiar stars in the LMC as compared to the Galaxy continues to be valid. Most of the photometrically identified peculiar stars (from their historical origin denominated Ap stars) are located in the domain of the B-type stars. However, this is a selection effect due to the limiting magnitude of our observing conditions impeding the observation of fainter main-sequence stars (Paunzen et al. 2005).

Furthermore, with the help of the ESO 2.2m WFI, observations of a 30' large field within the Small Magellanic Cloud were performed, containing several clusters and a total of about 100.000 stars. The reduction of this enormous amount of data is still in progress.