论文标题

钡星作为AGB星的S过程核合成的示踪剂I。28星具有独立衍生的AGB质量的恒星

Barium stars as tracers of s-process nucleosynthesis in AGB stars I. 28 stars with independently derived AGB mass

论文作者

Cseh, B., Világos, B., Roriz, M. P., Pereira, C. B., D'Orazi, V., Karakas, A. I., Soós, B., Drake, N. A., Junqueira, S., Lugaro, M.

论文摘要

钡(BA)恒星被富含在其以前的渐近巨型分支(AGB)伴侣恒星内部的慢速中子捕获(S-process)元件中富含的材料污染,该元素现在是白矮人。我们将单个BA星星的丰度模式与AGB核合成模型进行比较,以验证AGB模型质量是否与独立得出的AGB质量兼容。我们选择了28个BA恒星的样品,通过将恒星定位在HR图上并与进化轨道进行比较,可以为其提供自洽的光谱观察和分析和出色的质量测定。对于该样品星,我们以前考虑了以前和最近得出的元素丰度。然后,我们对这些S过程的元素丰度与来自Monash和Friuity理论数据集的不同AGB核合成模型进行了详细的比较。我们通过计算稀释因子来简化二进制传质,以匹配每个恒星的[Ce/fe]值时使用不同的AGB模型,然后我们将稀释的模型丰度与完整的BA-Star丰度模式进行了比较。我们的比较证实,以13C为主要中子来源的低质量,非旋转AGB恒星模型是绝大多数被考虑的BA恒星的污染物。在28颗恒星中,在21个情况下,模型与确定的丰度和独立衍生的AGB质量都非常吻合,尽管在16个情况下,观察到的NB,RU,RU,MO和/或ND,SM的含量高于所预测的。对于3星,我们仅通过考虑质量低于独立确定的模型来获得与丰度的匹配。最后,4颗恒星显示出比模型预测更高的第一个S过程峰值丰度值,这可能代表了物理和/或核合成过程的特征,该过程在此处考虑的一组模型中未表示。

Barium (Ba) stars are polluted by material enriched in the slow neutron capture (s-process) elements synthesised in the interior of their former asymptotic giant branch (AGB) companion star, which is now a white dwarf. We compare individual Ba star abundance patterns to AGB nucleosynthesis models to verify if the AGB model mass is compatible with independently derived AGB mass. We selected a sample of 28 Ba stars for which both self-consistent spectroscopic observation and analysis are available and stellar mass determinations, via positioning the star on the HR diagram and comparing with evolutionary tracks. For this sample stars we considered both previously and recently derived elemental abundances. Then, we performed a detailed comparison of these s-process elemental abundances to different AGB nucleosynthesis models from the Monash and the FRUITY theoretical data sets. We simplified the binary mass transfer by calculating dilution factors to match the [Ce/Fe] value of each star when using different AGB models, and we then compared the diluted model abundances to the complete Ba-star abundance pattern. Our comparison confirms that low mass, non-rotating AGB stellar models with 13C as the main neutron source are the polluters of the vast majority of the considered Ba stars. Out of the 28 stars, in 21 cases the models are in good agreement with both the determined abundances and the independently derived AGB mass, although in 16 cases higher observed abundances of Nb, Ru, Mo and/or Nd, Sm than predicted. For 3 stars we obtain a match to the abundances only by considering models with masses lower than those independently determined. Finally, 4 stars show much higher first s-process peak abundance values than the model predictions, which may represent the signature of a physical and/or nucleosynthetic process that is not represented in the set of models considered here.

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