Abundance Patterns in Hot Subdwarf B Stars: The Case of Carbon

Details Abundance Patterns in Hot Subdwarf B Stars: The Case of Carbon Abundance Patterns in Hot Subdwarf B Stars: The Case of Carbon

May 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aipc.1135..148c&link_type=abstract

FUTURE DIRECTIONS IN ULTRAVIOLET SPECTROSCOPY: A Conference Inspired by the Accomplishments of the Far Ultraviolet Spectroscopic

Computer Science

Star Formation, Photometric, Polarimetric, And Spectroscopic Instrumentation, Cosmology

Scientific paper

One of the most puzzling phenomena observed at the surface of sdB stars is their abundance anomalies. For instance, high-resolution optical spectroscopy shows that the C abundance is lower than the solar abundance by about a factor of ten on average. A few stars, however, show a solar abundance or an abundance higher than solar. Although optical spectroscopy allows the measurement of relatively high C abundance, it fails to provide stringent upper limits when no C lines are detected. The Far Ultraviolet Spectroscopic Explorer (FUSE) comes to the rescue when no C lines are detected in the optical, because it is 1,000 times more sensitive than the VLT for the purpose of measuring very small amounts of C in the atmospheres of sdB stars. We measure the C abundance in the FUSE spectra of 30 stars. We confirm the C abundance trend reported in previous studies, but report the disappearance of C in five stars. The upper limits that we measure for these stars are about four orders of magnitude lower than the solar abundance. The observation of very low C abundance suggests that the normal equilibrium between gravitation and radiative levitation has been disrupted, perhaps by a weak stellar wind.

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