Chemical Abundances Along the Horizontal Branch

Horizontal-branch stars are tempting targets for chemical abundance analysis via high-resolution spectroscopy, as they are reasonably luminous and span a wide range of effective temperature, so that the absorption lines of many different chemical species can be observed. The cooler HB stars provide useful checkpoints for tracing the chemical evolution of low-mass stars between the red giant branch and asymptotic giant branch stages. The hotter HB stars, however, display surface abundances which are greatly altered by diffusion effects in their atmospheres. Although these abundance variations make it difficult (if not impossible) to assess the true abundance development of these stars, they provide interesting insights into atmospheric structure and dynamics.