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arXiv · 0804.1731

Twenty-three new ultra-cool subdwarfs from the Sloan Digital Sky Survey

Sebastien Lepine·Ralf-Dieter Scholz
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Abstract

A search of the Sloan Digital Sky Survey spectroscopic database has turned up 23 new ultra-cool subdwarfs, low-mass metal-poor stars of spectral subtype M 7.0 or later. Spectra from these red objects all show very strong molecular bands of CaH but relatively weak bands of TiO, indicative of a cool, metal-poor atmosphere. Five of the stars are formally classified as M subdwarfs (sdM7.0-sdM8.5), 13 as more metal-poor extreme subdwarfs (esdM7.0-esdM8.0), and five as extremely metal-poor ultra subdwarfs (usdM7.0-usdM7.5). In the [H_r,r-z] reduced proper motion diagram, these subdwarfs clearly populate the locus of low-luminosity stars with halo kinematics. It is argued that the objects are all very low-mass, metal-poor stars from the Galactic halo (Population II). These new discoveries more than double the census of spectroscopically confirmed ultra-cool subdwarfs. We show that the stars stand out remarkably in the [g-r,r-i] color-color diagram; a proposed color and proper motion selection scheme is expected to be extremely efficient in identifying more of these old, very low mass stars in the vicinity of the Sun.

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Sebastien Lepine, Ralf-Dieter Scholz. 2008-04-10. Twenty-three new ultra-cool subdwarfs from the Sloan Digital Sky Survey. https://doi.org/10.1086/590183

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