Investigations of Heavy Elements in Am and HgMn stars

Sammanfattning: The relationship between the HgMn and Am classes of chemically peculiar stars has been investigated primarily by observing abundances of heavy elements, including Pr, Nd, Hg, Tl and Bi. The main objective of the investigation has been to gather observational evidence to provide a better understanding of the mechanisms producing the abundance anomalies of these stars, and to establish the relationship between the two classes. The heavy elements generally show substantially larger enhancements in the HgMn than in the Am stars. The reason for this difference could be that the presence of a hydrogen convection zone in the Am stars limits the magnitude of the observed abundance enhancements, while its absence in the HgMn stars would make it possible for the elements to separate in the atmosphere itself and produce substantially larger enhancements. In this thesis the abundance of several elements derived from previous work has been plotted as a function of effective temperature in the temperature regime of the Am and HgMn stars. For several, predominantely heavy, elements the abundance changes very sharply in the boundary between Am and HgMn stars which could indicate a noticeable difference in their atmospheric structure.