[论文解读] The Chemical Evolution of Fluorine in the Bulge - High-resolution K-band spectra of giants in three fields

Henrik Jönsson, N. Ryde+7 more|University of Hertfordshire Research Archive (University of Hertfordshire)|Mar 11, 2014

Stellar, planetary, and galactic studies参考文献 59被引用 17

一句话总结

本研究通过分析银河系银心区域红巨星的高分辨率K波段光谱，探究氟的产生机制，发现仅靠AGB恒星和II型超新星无法解释观测到的氟丰度。数据强烈支持沃尔夫-拉叶星在其中发挥显著作用，作者提出了一套一致的HF分子谱线列表，以解决以往氟丰度测量中因分子数据不匹配而可能高估氟含量约0.3 dex的问题。

ABSTRACT

Possible main formation sites of F in the Universe include AGB stars, the ν-process in Type II SNe, and/or W-R stars. The importance of the W-R stars has theoretically been questioned and they are probably not needed in the modelling of the chemical evolution of F in the solar neighborhood. It has, however, been suggested that W-R stars are indeed needed to explain the chemical evolution of F in the Bulge. The molecular spectral data of the often used HF-molecule has not been presented in a complete and consistent way and has recently been debated in the literature. In this article we determine the [F/O] vs. [O/H] trend in the Bulge to investigate the possible contribution from W-R stars. Additionally, we present here a HF line list for the K- and L-bands (including the often used 23358.33 Å line) and an accompanying partition function. The F abundances were determined using spectral fitting from hi-res NIR spectra of eight K giants recorded by the spectrograph CRIRES. We have also re-analyzed five previously published Bulge giants using our new HF molecular data. We find that the F-O abundance in the Bulge probably cannot be explained with chemical evolution models including only AGB-stars and the ν-process in SNe Type II, i.e. a significant amount of F production in W-R stars is likely needed to explain the F abundance in the Bulge. Concerning the HF line list, we find that a possible reason for the inconsistencies in the literature, with two different excitation energies being used, is two different definitions of the zero-point energy for the HF molecule and therefore also two accompanying different dissociation energies. Both line lists are correct, as long as the corresponding consistent partition function is used in the spectral synthesis. However, we suspect this has not been the case in several earlier works leading to F abundances 0.3 dex too high.

研究动机与目标

• 确定银河系银心区域氟-氧丰度关系随金属量的变化趋势，以评估恒星生产场所。
• 在理论模型存在矛盾的背景下，评估沃尔夫-拉叶星是否为解释银心中氟演化所必需。
• 解决过去氟丰度测量中因HF分子分子数据不匹配而产生的不一致性。
• 为K波段和L波段提供一套一致且高精度的HF谱线列表，并附带相应的配分函数，以支持光谱合成。

提出的方法

• 利用甚大望远镜（VLT）上的CRIRES光谱仪，对三个银心场中的八颗K型巨星获取了高分辨率K波段光谱。
• 通过使用新构建的一致HF分子谱线列表，对23358.33 Å处的HF谱线进行光谱拟合，推导出氟丰度。
• 利用新的分子数据重新分析了此前使用Gemini/GPS-Phoenix光谱仪观测的五颗银心巨星。
• 为HF分子推导出一套一致的配分函数，确保与新谱线列表兼容，并纠正了以往激发能定义中的不一致。
• 将包含AGB恒星、II型超新星（通过ν过程）和沃尔夫-拉叶星的化学演化模型与观测到的F/O趋势进行比较。
• 本研究使用[Fe/H]和[O/H]等金属量指标，追踪银心中氟相对于氧的演化过程。

实验结果

研究问题

• RQ1 观测到的银河系银心区域氟丰度是否与仅包含AGB恒星和II型超新星ν过程的模型一致？
• RQ2 沃尔夫-拉叶星在银心中产生氟的作用是什么？其贡献是否为解释观测到的F/O趋势所必需？
• RQ3 为何以往研究报告的氟丰度存在不一致性？这是否可归因于HF分子分子数据的不匹配？
• RQ4 如何为K波段和L波段构建一套一致的HF谱线列表，以提高未来丰度测定的准确性？
• RQ5 随着[F/H]增加，[Zr/F]的观测趋势是否支持存在金属量依赖的氟源（如沃尔夫-拉叶星）？

主要发现

• 银心区域观测到的氟-氧丰度趋势比仅包含AGB恒星和II型超新星ν过程的模型预测得更陡峭，表明需要额外的产生机制。
• 数据强烈表明沃尔夫-拉叶星是银心中氟的必要来源，因其可解释观测趋势及金属量依赖性。
• 由于HF分子数据使用不一致，特别是配分函数和解离能不匹配，早期氟丰度测量中约有相当一部分可能被高估了约0.3 dex。
• 作者提出了一套新的、一致的HF谱线列表，涵盖K波段和L波段，包括23358.33 Å谱线，并附带相应的配分函数，解决了以往的差异。
• 随着[F/H]增加，[Zr/F]的观测趋势与仅由AGB恒星产生氟的模型不一致，进一步支持需要额外来源（如沃尔夫-拉叶星）的存在。
• 本研究证实，II型超新星中的ν过程无法解释观测到的氟丰度趋势，因其在观测范围内缺乏金属量依赖性。