论文标题

银河磁盘中ytterbium的化学演化

Chemical Evolution of Ytterbium in the Galactic Disk

论文作者

Montelius, M., Forsberg, R., Ryde, N., Jönsson, H., Afşar, M., Johanssen, A., Kaplan, K. F., Kim, H., Mace, G., Sneden, C., Thorsbro, B.

论文摘要

测量银河磁盘星中中子捕获元件的丰度是理解关键恒星和银河过程的重要组成部分。在光波长状态下,已经测量了许多不同的中子捕获元件,但是从红外H波段中,仅S过程中占主导的元素元素已被精确测量了大型磁盘恒星样品。到目前为止,仅在一小部分恒星中测量了R-Process较为主导的元素ytterbium。在这项研究中,我们旨在使用$λ_\ text {air} $ =16498Å的YB II线来测量本地磁盘巨头的Ytterbium(YB)丰度。我们还将所得的丰度趋势与CE和欧盟的丰度进行比较,以分析S-和R过程的贡献。我们使用光谱合成分析了具有高分辨率H波段光谱的30个K巨人。使用高分辨率光谱使用相同的方法对同一恒星进行了分析,但是由于恒星与[Fe/H]> 1-1的恒星混合问题,因此无法从这些光谱中确定Yb的丰度。在本分析中,我们利用从光学分析确定的恒星参数。我们确定了[Yb/fe] 0.1 dex的估计不确定性的YB丰度。从比较来看,[Yb/fe]的趋势紧随[EU/FE]趋势,并在已识别的S型恒星中具有清晰的S过程富集。从比较中,支持YB丰度的有效性,并支持对YB起源的理论预测大约40/60 s-/r-process贡献。这些结果表明,通过对红外光谱进行仔细和详细的分析,可以在-1.1 <[fe/h] <0.3的范围内为更广泛的冷却器巨头样本提供可靠的YB丰度。这对于进一步研究了YB的生产和R-Process通道的进一步研究,即红外的银河化学演化的关键。

Measuring the abundances of neutron-capture elements in Galactic disk stars is an important part of understanding key stellar and galactic processes. In the optical wavelength regime a number of different neutron-capture elements have been measured, however from the infrared H-band only the s-process dominated element cerium has been accurately measured for a large sample of disk stars. The more r-process dominated element ytterbium has only been measured in a small subset of stars so far. In this study we aim to measure the ytterbium (Yb) abundance of local disk giants using the Yb II line at $λ_\text{air}$=16498Å. We also compare the resulting abundance trend with Ce and Eu abundances for the same stars to analyse the s- and r-process contributions. We analyse 30 K-giants with high-resolution H-band spectra using spectral synthesis. The very same stars have already been analysed using high-resolution optical spectra using the same method, but the abundance of Yb was not possible to determine from those spectra due to blending issues for stars with [Fe/H]>-1. In this present analysis, we utilise the stellar parameters determined from the optical analysis. We determined the Yb abundances with an estimated uncertainty for [Yb/Fe] of 0.1 dex. From comparison, the trend of [Yb/Fe] follows closely the [Eu/Fe] trend and has clear s-process enrichment in identified s-rich stars. From the comparison, both the validity of the Yb abundances are ensured, and the theoretical prediction of a roughly 40/60 s-/r-process contribution to Yb's origin is supported. These results show that with a careful and detailed analysis of infrared spectra, reliable Yb abundances can be derived for a wider sample of cooler giants in the range -1.1<[Fe/H]<0.3. This is promising for further studies of the production of Yb and for the r-process channel, key for Galactochemical evolution, in the infrared.

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