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arXiv 1004.0863astro-ph.SR
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基于激发温度的晕矮星的锂丰度。II。NLTE

Lithium abundances of halo dwarfs based on excitation temperatures. II. NLTE

A. Hosford, A. E. Garcia Perez, R. Collet, S. G. Ryan, J. E. Norris, K. A. Olive

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12 pages, 10 Figures
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摘要：

决定恒星锂丰度的最重要因素之一是有效温度。在作者之前的研究中，使用Fe线形成的局部热力学平衡（LTE）描述推导出了16个贫金属晕矮星的新有效温度Teff。这个新的Teff量表加强了这种差异。对于我们以前研究中的六颗恒星，我们使用非局部热力学平衡（NLTE）方法计算了修订后的温度。然后，这些被用来获得一个新的平均原始锂丰度，试图解决锂的差异。使用代码MULTI，我们计算NLTE的LTE丰度的Fe I线测量的六颗星，并确定新的Teff的。我们将其他物理参数，即log g、[Fe/H]和xi保持在文献I中计算的值不变。利用修订后的Teff量表，我们得出了新的Li丰度。我们将Teff的NLTE值与Ryan等人（1999，ApJ，523，654）的测光温度、Melendez和Ramirez（2004，ApJ，615，33）的红外通量法（IRFM）温度以及Asplund等人（2006，ApJ，644，229）的Balmer线翼温度进行了比较。我们发现，我们的温度比Ryan等人和Asplund等人的温度高出约110 K - 160 K，但仍然比Melendez和Ramirez的温度低约190 K。温度意味着原始锂丰度为2.19 dex或2.21 dex，这取决于计算中与氢碰撞的大小，仍然远低于WMAP + BBN推断的2.72 dex值。讨论了碰撞对[Fe/H]和Teff ~ 7 Li丰度变化趋势的影响，以及NLTE对通过电离平衡确定log g的影响，这意味着Fe和H原子碰撞的碰撞标度因子SH > 1.

英文摘要：

One of the most important factors in determining the stellar lithium abundance is the effective temperature. In a previous study by the authors, new effective temperatures Teff for sixteen metal-poor halo dwarfs were derived using a local thermodynamic equilibrium (LTE) description of the formation of Fe lines. This new Teff scale reinforced the discrepancy. For six of the stars from our previous study we calculate revised temperatures using a non-local thermodynamic equilibrium (NLTE) approach. These are then used to derive a new mean primordial lithium abundance in an attempt to solve the lithium discrepancy. Using the code MULTI we calculate NLTE corrections to the LTE abundances for the Fe I lines measured in the six stars, and determine new Teff's. We keep other physical parameters, i.e. log g, [Fe/H] and xi, constant at the values calculated in Paper I. With the revised Teff scale we derive new Li abundances. We compare the NLTE values of Teff with the photometric temperatures of Ryan et al. (1999, ApJ, 523, 654), the infrared flux method (IRFM) temperatures of Melendez & Ramirez (2004, ApJ, 615, 33), and the Balmer line wing temperatures of Asplund et al. (2006, ApJ, 644, 229). We find that our temperatures are hotter than both the Ryan et al. and Asplund et al. temperatures by typically ~ 110 K - 160 K, but are still cooler than the temperatures of Melendez & Ramirez by typically ~ 190 K. The temperatures imply a primordial Li abundance of 2.19 dex or 2.21 dex, depending on the magnitude of collisions with hydrogen in the calculations, still well below the value of 2.72 dex inferred from WMAP + BBN. We discuss the effects of collisions on trends of 7Li abundances with [Fe/H] and Teff, as well as the NLTE effects on the determination of log g through ionization equilibrium, which imply a collisional scaling factor SH > 1 for collisions between Fe and H atoms.

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