半人马座欧米茄中最热的水平分支恒星：后期热闪焰与氦富集
The Hottest Horizontal-Branch Stars in omega Centauri - Late Hot Flasher vs. Helium Enrichment
摘要：
对一些大质量球状星团的紫外线观测发现，在水平分支（HB）的热端下方有大量非常热的恒星，即所谓的蓝钩星。这一特征可能被解释为后期热闪情景的结果，即恒星在白矮星冷却曲线上经历氦闪，或者被最近假设存在于某些星团中的富氦子种群的后代所解释。使用LTE和非LTE模型大气分析了欧米茄Cen蓝色HB热端恒星的中等高分辨率光谱的大气参数和丰度。在30，000 K到50，000 K的温度范围内，我们发现35%的恒星是贫氦的（log（n_He/n_H）< -2），51%的恒星的太阳氦丰度在3倍以内（-1.5 <= log（n_He/n_H）<= -0.5），14%的恒星是富氦的（log（n_He/n_H）> -0.4）。我们还发现碳富集与氦富集同步，最大碳富集为3质量%。至少有14%的半人马座最热的HB星的氦丰度远高于氦富集情景的最高预测值（Y = 0.42对应于log（n_He/n_H）~ -0.74）。此外，最富氦的恒星显示出强烈的碳富集，正如后期热闪光情景所预测的那样。我们的结论是，富含氦的HB星在欧米茄Cen不能被解释的氦富集的情况下调用来解释蓝色的主序列。（节录）
英文摘要：
UV observations of some massive globular clusters uncovered a significant population of very hot stars below the hot end of the horizontal branch (HB), the so-called blue hook stars. This feature might be explained either as results of the late hot flasher scenario where stars experience the helium flash while on the white dwarf cooling curve or by the progeny of the helium-enriched sub-population recently postulated to exist in some clusters. Moderately high resolution spectra of stars at the hot end of the blue HB in omega Cen were analysed for atmospheric parameters and abundances using LTE and Non-LTE model atmospheres. In the temperature range 30,000K to 50,000K we find that 35% of our stars are helium-poor (log(n_He/n_H) < -2), 51% have solar helium abundance within a factor of 3 (-1.5 <= log(n_He/n_H) <= -0.5) and 14% are helium-rich (log(n_He/n_H)> -0.4). We also find carbon enrichment in step with helium enrichment, with a maximum carbon enrichment of 3% by mass. At least 14% of the hottest HB stars in omega Cen show helium abundances well above the highest predictions from the helium enrichment scenario (Y = 0.42 corresponding to log(n_He/n_H) ~ -0.74). In addition, the most helium-rich stars show strong carbon enrichment as predicted by the late hot flasher scenario. We conclude that the helium-rich HB stars in omega Cen cannot be explained solely by the helium-enrichment scenario invoked to explain the blue main sequence. (Abridged)
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
