AAS 201st Meeting, January, 2003
Session 4. Eclipsing and Spectroscopic Binaries
Poster, Monday, January 6, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[4.03] Physical Parameters of the Metal-Poor Binary System HD 157948

J.N. Heasley (Univ. of Hawaii), O.G. Franz, L.H. Wasserman (Lowell Observatory), E.P. Horch (Univ. Mass. Dartmouth)

The metal-poor star HD 157948 ([Fe/H] = -0.75]) has been identified by Latham et al. (1992, A.J., 104, 774) as a doubled-lined spectroscopic binary with a period of 446.7 days. We have observed this star 5 times using the FGS on the Hubble Space Telescope as part of a program to determine the masses and luminosities of Population II stars. The FGS observations resolve HD 157948 into a triple-star system, with a close pair that corresponds to the spectroscopic double and wide fainter component. The tight inner pair has a projected orbit with a semi-major axis of ~20 mas and exhibits orbital motion consistent with the period determined from the spectroscopic observations. This pair has a magnitude difference of 0.4 as measured through the F583W filter on the FGS. The faint, distant component is ~280 mas from the primary star and is 2.3 magnitudes fainter. The wide componet has also been resolved at several wavelengths using the WIYN telescope. In this paper we present the physical parameters for the tight pair derived from a preliminary analysis of the HST astrometry combined with the radial velocity data from the literature.

This work is based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with proposal # 9034.

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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.