Bixler J V, Bowyer S, Laget M
Physics Department and Space Sciences Laboratory, University of California, Berkeley 94720, USA.
Astron Astrophys. 1991 Oct;250(2):370-88.
Optical spectra have been obtained for a selection of objects included in a catalog of far ultraviolet bright, high galactic latitude objects detected with a balloon-borne survey telescope. The observed objects provide a sample of subdwarf O and B stars, white dwarfs, and binary systems including a hot subluminous member. Model atmospheres analysis of the subdwarf sample is used to determine the temperature, gravity, and helium to hydrogen ratio of the individual objects. A smooth distribution of objects is found on the gravity versus temperature diagram near the theoretical location of the extended horizontal branch. A break between the helium rich and helium poor objects occurs at 40,000 K. Suspected binary objects were found and analyzed to determine the temperature and gravity of the hot subluminous member in each system. The number of subdwarf stars contained in binaries is determined to be from 65% to 100%. The number versus ultraviolet magnitude distribution of the subdwarf B sample is modeled to obtain a midplane density of 3.3 10(-6) pc-3 and a population scale height of 240 pc. The proportion of white dwarfs that experience the subdwarf phase of evolution is found to be 0.94%.
利用气球搭载的巡天望远镜，已获得一份远紫外亮、高银纬天体目录中部分天体的光谱。观测到的天体包括次矮星O和B型星、白矮星以及包含热亚矮星成员的双星系统样本。通过对次矮星样本进行模型大气分析，确定了各个天体的温度、引力以及氦氢比。在重力与温度关系图上，发现天体在延伸水平支的理论位置附近呈平滑分布。富氦天体与贫氦天体之间的分界线出现在40,000 K处。已发现并分析了疑似双星天体，以确定每个系统中热亚矮星成员的温度和引力。确定双星中所含次矮星的数量比例为65%至100%。对次矮星B样本的数量与紫外星等分布进行建模，得出中平面密度为3.3×10^(-6) pc^(-3)，总体标高为240 pc。发现经历次矮星演化阶段的白矮星比例为0.94%。
