arXiv 0907.13292009-07-08astro-ph.SR

用Na I 5890/5896谱线能可靠地测定A型星的钠丰度吗？

Can Sodium Abundances of A-Type Stars Be Reliably Determined from Na I 5890/5896 Lines?

Yoichi Takeda, Dong-Il Kang, Inwoo Han, Byeong-Cheol Lee, Kang-Min Kim

备注：: 14 pages, 8 figures, accepted for publication in Publ. Astron. Soc. Japan, Vol. 61, No. 5 (2009)
DOI：: 10.1093/pasj/61.5.1165

摘要：

对120颗A型主序星（包括23颗毕宿星）进行了基于Na I 5890/5896双重线的非LTE丰度分析，目的是检验是否可以根据这些强Na I D线可靠地确定A型矮星的Na丰度。通过应用T_eff相关的微湍流速度（T_eff ~2--4 km/s，峰值在T_eff ~ 8000 K（A星的典型值））得到的丰度（[Na/H]_{58}）通常为负，差异很大（从~-1到~0），同时显示v_e sin i相关的迹象（向更高的旋转方向减小）。然而，这种明显的日下趋势的真实性是非常值得怀疑的，因为这些[Na/H]_{58}系统地比更可靠的[Na/H]_{61}（从锐线星的弱Na I 6154/6161线导出）低~0.3--0.6 dex。考虑到这些饱和Na I D线的丰度对α的敏感性，我们认为[Na/H]_{58}一定是被错误地低估了，我们怀疑，至少对于这样强的高形成Na I 5890/5896线，常规α值是不适当地太大了，这大概是由于α随高度而减小的深度依赖性。在我们能够从这些强共振D线确定可靠的钠丰度之前，必须对A星中后期大气湍流速度场的性质进行更多的研究。

英文摘要：

An extensive non-LTE abundance analysis based on Na I 5890/5896 doublet lines was carried out for a large unbiased sample of ~120 A-type main-sequence stars (including 23 Hyades stars) covering a wide v_e sin i range of ~10--300 km/s, with an aim to examine whether the Na abundances in such A dwarfs can be reliably established from these strong Na I D lines. The resulting abundances ([Na/H]_{58}), which were obtained by applying the T_eff-dependent microturbulent velocities of ξ~2--4 km/s with a peak at T_eff ~ 8000 K (typical for A stars), turned out generally negative with a large diversity (from ~-1 to ~0), while showing a sign of v_e sin i-dependence (decreasing toward higher rotation). However, the reality of this apparently subsolar trend is very questionable, since these [Na/H]_{58} are systematically lower by ~0.3--0.6 dex than more reliable [Na/H]_{61} (derived from weak Na I 6154/6161 lines for sharp-line stars). Considering the large ξ-sensitivity of the abundances derived from these saturated Na I D lines, we regard that [Na/H]_{58} must have been erroneously underestimated, suspecting that the conventional ξvalues are improperly too large at least for such strong high-forming Na I 5890/5896 lines, presumably due to the depth-dependence of ξdecreasing with height. The nature of atmospheric turbulent velocity field in mid-to-late A stars would have to be more investigated before we can determine reliable sodium abundances from these strong resonance D lines.

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。

摘要：

英文摘要：

相关论文