SIMBAD references

The surface abundance patterns of 13 sdB stars have been determined from high resolution, high S/N, optical spectra. As typical in early B type stars, the metal lines are few and very weak. The metal abundance patterns are compared with the atmospheric parameters to search for possible trends, which are predicted by diffusion theory. However, it is remarkable that some metals (e.g. N, Mg, Fe) have similar abundances irrespective of the stellar parameters, whereas other metals (e.g. C, O) and the helium abundances vary considerably from star to star. Three peculiar sdB stars were found which show an enormous enrichment of iron group elements. An isotopic anomaly of helium has been found in two sdB stars. In these stars ⁴He is largely replaced by the isotope ³He. We discovered additionally four single lined, short period radial velocity variable sdB stars and measured their radial velocity curves.