Rubidium and zirconium abundances in massive Galactic asymptotic giant branch stars revisited
Rubidium and zirconium abundances in massive Galactic asymptotic giant branch stars revisited
复制标题
重新审视巨大的银河渐近巨分支恒星中的铷和锆丰度
DOI：
10.1051/0004-6361/201731245
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
M. Lugaro
中科院分区：
文献类型：
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作者：
V. Pérez;V. Pérez;O. Zamora;O. Zamora;D. A. García;D. A. García;B. Plez;A. Manchado;A. Manchado;Amanda I Karakas;M. Lugaro
发光的银河系OH/IR星被确定为正在经历HBB和Li产生的大质量(>；4-5M_S)AGB星。它们的Rb丰度和来自流体静力模式大气的[Rb/Zr]比明显高于AGB核合成模型的预测值，这给我们理解AGB演化和核合成带来了困难。我们报告了以前用流体静力模型研究的大质量银河系AGB恒星的全样本中新的Rb和Zr丰度，通过使用更真实的扩展模型大气。我们使用谱合成程序Turbspectrum的修改版本，并考虑了星周包络和径向风的存在。分别从7800ARbI共振线和6474AZrO带头测量了Rb丰度和Zr丰度，并讨论了在扩展模型中所得到的丰度对恒星(Tef)和风参数(M损失、β和Vexp)变化的敏感性。由最佳光谱拟合得到的Rb和Zr丰度与最新的AGB核合成理论模型进行了比较。新的Rb丰度比用流体静力学模型得到的Rb丰度要低得多(甚至1-2Dex)，而用流体静力模型计算的Rb丰度与用静力模型得到的结果相近。RbI线剖面和Rb丰度对M_损失率非常敏感，但对风速律和Vexp(OH)的变化不太敏感。我们证实了早期基于大质量富氧AGB星小样本的初步结果，即使用扩展大气模型可以解决AGB核合成理论模型与银河系大质量AGB星观测之间的差异。然而，Rb丰度仍然强烈依赖于M_Loss，这在这些AGB星中是未知的。这些大质量银河系AGB星需要准确的M_损失率，才能打破模型的简并性，得到可靠的Rb丰度。
Luminous Galactic OH/IR stars have been identified as massive (>4-5 M_s) AGB stars experiencing HBB and Li production. Their Rb abundances and [Rb/Zr] ratios derived from hydrostatic model atmospheres, are significantly higher than predictions from AGB nucleosynthesis models, posing a problem to our understanding of AGB evolution and nucleosynthesis. We report new Rb and Zr abundances in the full sample of massive Galactic AGB stars, previously studied with hydrostatic models, by using more realistic extended model atmospheres. We use a modified version of the spectral synthesis code Turbospectrum and consider the presence of a circumstellar envelope and radial wind. The Rb and Zr abundances are determined from the 7800 A Rb I resonant line and the 6474 A ZrO bandhead, respectively, and we explore the sensitivity of the derived abundances to variations of the stellar (Teff) and wind (M_loss, beta and vexp) parameters in the extended models. The Rb and Zr abundances derived from the best spectral fits are compared with the most recent AGB nucleosynthesis theoretical models. The new Rb abundances are much lower (even 1-2 dex) than those derived with the hydrostatic models, while the Zr abundances are similar. The Rb I line profile and Rb abundance are very sensitive to the M_loss rate but much less sensitive to variations of the wind velocity-law and the vexp(OH). We confirm the earlier preliminary results based on a smaller sample of massive O-rich AGB stars, that the use of extended atmosphere models can solve the discrepancy between the AGB nucleosynthesis theoretical models and the observations of Galactic massive AGB stars. The Rb abundances, however, are still strongly dependent of the M_loss, which is unknown in these AGB stars. Accurate M_loss rates in these massive Galactic AGB stars are needed in order to break the models degeneracy and get reliable Rb abundances in these stars.