Other
Scientific paper
Jul 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996hst..prop.6649p&link_type=abstract
HST Proposal ID #6649
Other
Hst Proposal Id #6649 Cool Stars
Scientific paper
We propose to obtain high-resolution GHRS ECH-B spectra of the boron region near 2495Angstrom of RR Lyrae, the prototype pulsating variable star, to establish the characteristics of possible blends affecting B I lines. GHRS spectra of B I lines have been obtained for a wide variety of stars, from Procyon {F4 IV} to giants such as the Hyades {K0 III} and to extremely metal-poor stars. The resulting boron abundances shed light on mixing and dilution processes during stellar evolution and the early history of light-element abundances in the oldest stars. These results are compromised if unidentified lines contaminate the B I features of interest. For example, the ECH -B observations of Procyon yield only an upper limit in two separate investigations because of this possibility. We will establish the nature of any such blends by observing RR Lyrae, a moderately-metal-poor star which undergoes a temperature change of about 1000K during the course of each cycle {0.57 day}. Being a core-helium-burning star whose current photosphere was once buried deep in the convective zone, RR Lyrae is expected to have a very low boron abundance and is sharp-lined at almost all phases, so blends will stand out. By mapping the strength of any absorption near the B I line positions with phase and therefore temperature, we will be able to discern whether blends are present and how they strengthen and weaken at other temperatures and abundances. This knowledge will lead to more accurate boron abundances for stars with existing HRS spectra.
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