Atmospheres, Chemical Compositions, and Evolutionary Histories of Very Metal-Poor Red Horizontal-Branch Stars in the Galactic Field and in NGC 7078 (M15)

Abstract

We have conducted spectrum analyses of 24 field metal-poor ([Fe/H] 30deg) brighter than V=15 exceeds those identified in extant objective-prism surveys by more than an order of magnitude. Finally, we deduce the effective temperature of the fundamental red edge of the metal-poor RR Lyrae instability strip, logTeff(FRE)=3.80+/-0.01, from the interface between the temperature distributions of metal-poor field RHB stars and the RR Lyrae stars of similar [Fe/H] in five metal-poor globular clusters. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center, California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This paper includes data gathered with the 6.5 m Magellan telescopes located at Las Campanas Observatory, Chile.