标题： 两颗矮碳星的天体测量学和 photometry 显示英文标题

标题： Astrometry and Photometry for Two Dwarf Carbon Stars

摘要： 给出了两个矮碳星 LP765-18 (= LHS1075) 和 LP328-57 (= CLS96) 的初步三角视差和 BVI 光度数据。这些数据与文献中第三个矮碳星 G77-61 (= LHS1555) 的值相结合。 这三颗恒星的光度（9.6 < M_V < 10.0）非常相似，并且在整个可见光到近红外（BVIJHK）波长范围内宽带颜色也非常相似。它们的视觉（BVI）颜色与所有已知的红矮星、次矮星和白矮星都不同。 在 M_V 对 V-I 颜色-亮度图中，它们比具有类似太阳金属丰度的正常盘状矮星低约 2 个星等，也占据了由富含氧的次矮星（-1.5 < [m/H] < -1.0）占据的区域。 运动学表明它们是银河系球状晕星族的成员。 这三颗恒星的次亮性归因于一种尚未确定的组合因素，包括（无疑很低的）金属丰度、可能增强的氦丰度以及所考虑的波段中的异常线吸收。 恒星的性质与矮碳星形成模型进行了比较。 显示英文摘要

摘要： Preliminary trigonometric parallaxes and BVI photometry are presented for two dwarf carbon stars, LP765-18 (= LHS1075) and LP328-57 (= CLS96). The data are combined with the literature values for a third dwarf carbon star, G77-61 (= LHS1555). All three stars have very similar luminosities (9.6<M_V<10.0) and very similar broadband colors across the entire visual-to-near IR (BVIJHK) wavelength range. Their visual (BVI) colors differ from all known red dwarfs, subdwarfs, and white dwarfs. In the M_V versus V-I color-magnitude diagram they are approximately 2 magnitudes subluminous compared with normal disk dwarfs with solar-like metallicities, occupying a region also populated by O-rich subdwarfs with -1.5<[m/H]<-1.0. The kinematics indicate that they are members of the Galactic spheroid population. The subluminosity of all three stars is due to an as-yet-unknown combination of (undoubtedly low) metallicity, possibly enhanced helium abundance, and unusual line-blanketing in the bandpasses considered. The properties of the stars are compared with models for the production of dwarf carbon stars.