arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2005.06807astro-ph.SRastro-ph.GA
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半人马座Omega富金属红巨星的氦增强

Helium Enhancement in the Metal Rich Red Giants of Omega Centauri

B. P. Hema, Gajendra Pandey, R. L. Kurucz, C. Allende Prieto

摘要:

富氦半人马座欧米茄中富含(He)金属的红巨星,由Hema和Pandey使用Vainu Bappu望远镜(VBT)的低分辨率光谱发现,并通过分析从HRS-South African Large Telescope(SALT)获得的LEID 34225和LEID 39048的高分辨率光谱得到证实,在这里重新分析,以确定其程度的氦增强/氢缺乏(H-缺乏)。所观察到的MgH带结合模型大气具有不同的He/H比用于分析。这两颗巨星的He/H比是通过强制执行这样一个事实来确定的,即对于所采用的模型大气,从MgI谱线和从MgH谱带的从属谱线导出的Mg丰度必须相同。LEID 34225和LEID 39048的估计He/H比分别为0.15+/-0.04和0.20+/-0.04,而正常He/H比为0.10。根据对其他两颗比较星(LEID 61067和LEID 32169)的分析,得到正常的He/H比为0.10。0.15-0.20的He/H比对应于大约0.375-0.445的氦的质量分数(Z(He)=Y)。氦增强的范围和衍生的金属丰度的程序星是符合确定的欧米茄Cen蓝色主序星。因此,我们的研究为富含金属的氦增强型欧米茄Centuari种群的进化轨迹提供了缺失的环节。这项研究工作是第一次使用MgI和MgH线对半人马座欧米茄富含金属的红巨星中He增强量进行光谱测定。

英文摘要:

The helium-enriched (He-enriched) metal-rich red giants of Omega Centauri, discovered by Hema and Pandey using the low-resolution spectra from the Vainu Bappu Telescope (VBT) and confirmed by the analyses of the high-resolution spectra obtained from the HRS-South African Large Telescope (SALT) for LEID 34225 and LEID 39048, are reanalysed here to determine their degree of He-enhancement/hydrogen-deficiency (H-deficiency). The observed MgH band combined with model atmospheres with differing He/H ratios are used for the analyses. The He/H ratios of these two giants are determined by enforcing the fact that the derived Mg abundances from the MgI lines and from the subordinate lines of the MgH band must be same for the adopted model atmosphere. The estimated He/H ratios for LEID 34225 and LEID 39048 are 0.15+/-0.04 and 0.20+/-0.04, respectively, whereas the normal He/H ratio is 0.10. Following the same criteria for the analyses of the other two comparison stars (LEID 61067 and LEID 32169), a normal He/H ratio of 0.10 is obtained. The He/H ratio of 0.15-0.20 corresponds to a mass fraction of helium (Z(He)=Y) of about 0.375-0.445. The range of helium enhancement and the derived metallicity of the program stars are in line with those determined for Omega Cen blue main-sequence stars. Hence, our study provides the missing link for the evolutionary track of the metal-rich helium-enhanced population of Omega Centuari. This research work is the very first spectroscopic determination of the amount of He-enhancement in the metal-rich red giants of Omega Centauri using the MgI and MgH lines.

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