NOAO >   Observing Info >   Approved Programs >   2002B-0139

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Proposal Information for 2002B-0139


PI: Michele Stark, The Pennsylvania State University, stark@astro.psu.edu
Address: 525 Davey Lab, State College, PA 16802, USA

CoI: Richard Wade, The Pennsylvania State University

Title: Determining the Properties of Hot Subdwarf Star Composite Binaries

Abstract: Hot subdwarf (sdB) stars are believed to be the field equivalent of the extended horizontal branch stars seen in some globular clusters. We have identified a large sample of sdB stars that exhibit infrared excesses, which can be attributed to the presence of an unresolved late- type companions of G-K spectral type. The presence of companions is expected if the post-main sequence mass loss of these stars is due to binary interactions. We propose to obtain moderate resolution spectra of a subset of these stars in the regions of 4500-7000A and 6500- 9000A in order to study features from the cool companion of the sdB stars. We will use the Ca \scshapeii IR triplet (8498, 8542, 8662A), the Na \scshapei D doublet (5889, 5895A), and the Mg \scshapei b triplet (5167, 5172, 5183A) from the cool companion, along with existing photometry, to decompose the composite sdB+late type spectrum to determine the spectral type, luminosity class, and fraction of the total light contributed by the cooler component. Using this information about the cool component, we can independently constrain the luminosity of sdB stars independent of any uncertainties in the modeling of the subdwarfs' spectrum, along with providing constraints on the age, progenitor initial mass, and total post-main sequence mass loss of the sdB star.


National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360



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