A HELIUM–CARBON CORRELATION ON THE EXTREME HORIZONTAL BRANCH IN ω CENTAURI
A HELIUM–CARBON CORRELATION ON THE EXTREME HORIZONTAL BRANCH IN ω CENTAURI
复制标题
半人马座ω极端水平分支上的氦-碳相关性
DOI：
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
P. Brassard
中科院分区：
文献类型：
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作者：
M. Latour;S. Randall;G. Fontaine;G. Bono;A. Calamida;P. Brassard
Taking advantage of a recent FORS2/VLT spectroscopic sample of extreme horizontal branch (EHB) stars in ω Cen, we isolate 38 spectra well suited for detailed atmospheric studies and determine their fundamental parameters (Teff, log g, and log N(He)/N(H)) using NLTE, metal line-blanketed models. We find that our targets can be divided into three groups: 6 stars are hot (Teff ≳ 45,000 K) H-rich subdwarf O stars, 7 stars are typical H-rich sdB stars (Teff ≲ 35,000 K), and the remaining 25 targets at intermediate effective temperatures are He-rich (log N(He)/N(H) ≳ −1.0) subdwarfs. Surprisingly, and quite interestingly, these He-rich hot subdwarfs in ω Cen cluster in a narrow temperature range (∼35,000 K to ∼40,000 K). We additionally measure the atmospheric carbon abundance and find a most interesting positive correlation between the carbon and helium atmospheric abundances. This correlation certainly bears the signature of diffusion processes—most likely gravitational settling impeded by stellar winds or internal turbulence—but also constrains possible formation scenarios proposed for EHB stars in ω Cen. For the He-rich objects in particular, the clear link between helium and carbon enhancement points toward a late hot flasher evolutionary history.
