斯隆数字巡天获得的23颗新超酷亚矮星
Twenty-three new ultra-cool subdwarfs from the Sloan Digital Sky Survey
摘要：
对斯隆数字巡天光谱数据库的搜索发现了23个新的超冷次矮星，光谱亚型M 7.0或更高的低质量贫金属恒星。这些红色天体的光谱都显示出非常强的CaH分子带，但TiO的分子带相对较弱，表明大气层温度低，金属含量低。其中5颗恒星被正式归类为M型次矮星（sdM7.0-sdM8.5），13颗被归类为贫金属的极端次矮星（esdM7.0-esdM8.0），5颗被归类为极贫金属的超次矮星（usdM7.0-usdM7.5）。在[H_r，r-z]约化自行图中，这些次矮星明显地占据了具有晕运动学的低光度星的轨迹。有人认为，这些天体都是来自星系晕（星族II）的质量非常低、金属贫乏的恒星。这些新发现使光谱学证实的超冷次矮星的数量增加了一倍多。我们发现，恒星在[g-r，r-i]色-色图中非常突出;提出的颜色和自行选择方案预计将非常有效地识别太阳附近更多的这些古老的、质量很低的恒星。
英文摘要：
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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