标题： omega 半人马座中“蓝钩”星的光谱分析：晚期热闪模型的检验 显示英文标题

标题： Spectroscopic Analyses of the "Blue Hook" Stars in omega Centauri: A Test of the Late Hot Flasher Scenario

摘要： 半人马座 ω 含有已知球状星团中最庞大的非常炽热水平分支（HB）星群体。最近的紫外观测（Whitney 等，1998年；D'Cruz 等，2000年）显示，在零龄水平分支以下存在显著数量的炽热恒星（“蓝色钩子”星），这些恒星无法通过经典的恒星演化理论解释。那些在红巨星分支上经历异常大质量损失并因此在白矮星冷却曲线下降时经历氦闪的恒星可能占据这一区域。理论预测这些“晚期炽热闪焰者”应该比最炽热的经典HB星温度更高，并且拥有富含氦和碳的大气层。我们获取并分析了一组蓝色钩子星的中等分辨率光谱以推导它们的大气参数。蓝色钩子星确实比经典的极端HB星更热（有效温度 > 35,000 K）且氦元素更丰富。此外，我们还发现相对于星团丰度，碳元素的丰度有显著增强。 显示英文摘要

摘要： omega Cen contains the largest population of very hot horizontal branch (HB) stars known in a globular cluster. Recent UV observations (Whitney et al. 1998; D'Cruz et al. 2000) show a significant population of hot stars below the zero-age horizontal branch (``blue hook'' stars), which cannot be explained by canonical stellar evolution. Stars which suffer unusually large mass loss on the red giant branch and thus experience the helium core flash while descending the white dwarf cooling curve could populate this region. Theory predicts that these ``late hot flashers'' should show higher temperatures than the hottest canonical HB stars and should have helium- and carbon-rich atmospheres. We obtained and analysed medium resolution spectra of a sample of blue hook stars to derive their atmospheric parameters. The blue hook stars are indeed both hotter (Teff > 35,000K) and more helium-rich than classical extreme HB stars. In addition we find indications for a large enhancement of the carbon abundance relative to the cluster abundance.