出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：Subluminous B stars (sdB) are core helium burning stars of about half a solar mass. A new
class of non-radial pulsators has recently been discovered amongst them at temperatures between
29 000K and 35 000K. The richness of the pulsation modes makes these stars ideal targets for
asteroseismology. We present a detailed abundance analysis of high-resolution ultraviolet echelle
spectra of five subdwarf B stars obtained using the Space Telescope Imaging Spectrograph on
board the Hubble Space Telescope. The goal of our observations was to test the hypothesis that
pulsations in sdBs are correlated to the surface abundances of iron-group elements. We study
two pulsators and three non-pulsators. We determined abundances for 25 elements including
the iron group and even heavier elements such as tin and lead using LTE curve-of-growth and
spectrum synthesis techniques and find strong enrichment of heavy elements up to 2.9 dex with
respect to solar which are probably caused by atomic diffusion processes. We find that there is no
clear correlation between pulsations and metal abundances. This poses a serious challenge to the
diffusion and pulsation theory.
Abundances for the lead isotopes are derived from very high resolution spectra using an UV line
of triply ionised lead. As Pb terminates the s-process sequence its isotopic abundance ratios yield
important constraints for understanding stellar nucleosynthesis. It is very difficult to measure
them in hot stars. For the first time we were able to determine them in two subluminous B stars
and conclude that their 207Pb/208Pb are solar
