Metal abundances of sdB stars

A semi-automatic analysis pipeline was developed to calculate and fit LTE models to a standard set of spectral lines. A general trend of enrichment was found with increasing temperature for most of the heavier elements. The lighter elements like carbon, oxygen and nitrogen are depleted and less affected by temperature.

Although there is considerable scatter from star to star, the general abundance patterns in most sdBs are similar. State-of-the-art diffusion models predict such patterns and are in qualitative agreement with our results. However, the highest enrichments measured cannot not be explained with these models.

Peculiar line shapes of the strongest metal lines in some stars indicate vertical stratification to be present in the atmospheres. Such effects are not accounted for in current diffusion models and may be responsible for some of the yet unexplained abundance anomalies.