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Astron. Astrophys. 360, 1077-1085 (2000)

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1. Introduction

The star CS 22873-139 was identified as an extremely metal-poor candidate [FORMULA] in the HK objective-prism/interference-filter survey of Beers et al. (1985, 1992).

Its magnitude is [FORMULA] and its coordinates are


Owing to its relatively bright apparent magnitude, CS 22873-139 is an attractive target for high-resolution observations in order to determine its elemental abundances, in spite of the difficulties introduced by its binarity.

Preston (1994) carried out an initial study of this star, obtaining a period estimate of 19.16 days, and a mass ratio of the two components 0.86[FORMULA] [FORMULA] [FORMULA] 0.9. Preston's model-dependent "decomposition" of CS 22873-139 led him to argue that the primary component might be classified as a "blue metal-poor main-sequence" star (BMP), as described in more detail by Preston et al. (1994). Furthermore, his comparison of the estimated luminosity ratios of the two components with the measured mass ratio suggested compatibility with an age of the system on the order of [FORMULA] 8 Gyr, which is surprisingly young for such a metal-deficient star. His conclusion was that this star may have been accreted from a low-luminosity satellite of the Milky Way sometime in the relatively recent past.

However, the spectroscopic data which Preston had available was of relatively low resolution ([FORMULA]) and signal-to-noise ratio ([FORMULA]), hence it was not feasible to derive accurate abundances for individual elements, and we sought to obtain data of the required quality, as examination of the relative elemental abundances might provide important clues to the origin of this star.

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© European Southern Observatory (ESO) 2000

Online publication: August 23, 2000