MK spectral types were determined for 263 B and A stars in the southern galactic clusters NGC 2287, 2422, 2451, 2516, 2547, 3228, and 3532 in order to investigate the frequency of Ap stars in galactic clusters. It was concluded that Ap stars of the Hg-Mn type could not be reliably identified at classification dispersion. Only Ap stars of the Si, Sr, Cr, or Eu types were considered. If one disregards photometric membership criteria for the Ap stars but not the normal stars, then there are 11 Ap stars and 203 normal B5 to A5 stars in these clusters. This frequency is lower than that found in two field samples. When this sample is combined with published data for other clusters, one has a sample which includes 38 Ap stars and 744 normal B5 to A5 stars. A chi squared test indicates that this frequency is lower than the field frequency at the 98.8 percent and 96.6 percent confidence levels for two field samples. Several systematic effects that may have influenced this result are investigated.
- Pub Date:
- Physics: Astronomy and Astrophysics;
- Galactic Clusters;
- Spectrum Analysis;