Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002hst..prop.9491b&link_type=abstract
HST Proposal ID #9491
Astronomy and Astrophysics
Astrophysics
Hst Proposal Id #9491
Scientific paper
Oxygen is critical in numerous astrophysical contexts, including the derivation of globular cluster ages and the early history of the Galaxy's chemistry. However, its abundance, particularly in metal-poor stars, remains controversial, with optical, IR and UV abundance indicators in dwarfs and giants yielding different abundance patterns; a flat O/Fe ratio with Fe/H is suggested by OI and IR-OH lines, while a monotonically increasing O/Fe trend with decreasing Fe/H is measured from OI and UV-OH lines with a factor of 10 difference at Fe/H=-3. We propose an in-depth study of the UV- OH lines in the halo subgiant HD 140283 with R=110, 000 and S/N=200 spectra and state-of-the-art 3-D model atmospheres. Understanding UV-OH lines is particularly important because these provide the sole means of measuring the oxygen abundance in the most metal-poor stars and therefore in the early Galaxy. STIS will for the first time provide several dozen unblended UV-OH lines. Predictions about the variation of line strength with excitation potential and the asymmetries of the OH line profiles will be tested and used to refine the cool outer layers of the 3-D models where the OH lines are formed. The end result will be an accurate oxygen abundance, a thorough understanding of OH line formation, and a good characterization of the atmosphere of a metal-poor star.
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