[论文解读] Stellar population astrophysics (SPA) with the TNG. Revisiting the metallicity of Praesepe (M44)

V. D’Orazi, E. Oliva+9 more|arXiv (Cornell University)|Nov 14, 2019

Stellar, planetary, and galactic studies参考文献 55被引用 9

一句话总结

本研究利用特里亚诺斯望远镜（TNG）上的GIARPS仪器获取的高分辨率光学与近红外光谱，重新评估了年轻疏散星团Praesepe（M44）的金属丰度。通过对十颗类太阳主序星实施严格差分分析，发现Praesepe的[Fe/H] = +0.21 ± 0.01 dex，显著高于Hyades星团的[Fe/H] = +0.16 ± 0.01 dex，挑战了这两个星团起源于同一来源的假说，并确立Praesepe为太阳系附近最富金属的年轻星团。

ABSTRACT

Open clusters exquisitely track the Galactic disc chemical properties and its time evolution; a substantial number of studies and large spectroscopic surveys focus mostly on the chemical content of relatively old clusters (age $\gtrsim$ 1 Gyr). Interestingly, the less studied young counterpart populating the solar surrounding has been found to be solar (at most), with a notable surprising lack of young metal-rich objects. While there is wide consensus about the moderately above-solar composition of the Hyades cluster, the metallicity of Praesepe is still controversial. Recent studies suggest that these two clusters share identical chemical composition and age, but this conclusion is disputed. With the aim of reassessing the metallicity of Praesepe, and its difference (if any) with the Hyades cluster, we present in this paper a spectroscopic investigation of ten solar-type dwarf members. We exploited $GIARPS$ at the TNG to acquire high-resolution, high-quality optical and near-IR spectra and derived stellar parameters, metallicity ([Fe/H]), light elements, $α$- and iron-peak elements, by using a strictly differential (line-by-line) approach. We also analysed in the very same way the solar spectrum and the Hyades solar analogue HD 28099. Our findings suggest that Praesepe is more metal-rich than the Hyades, at the level of $Δ$[Fe/H]=+0.05$\pm$0.01 dex, with a mean value of [Fe/H]=+0.21$\pm0.01$ dex. All the other elements scale with iron, as expected. This result seems to reject the hypothesis of a common origin for these two open clusters. Most importantly, Praesepe is currently the most metal-rich, young open cluster living in the solar neighbourhood.

研究动机与目标

• 由于先前结果存在矛盾，重新评估位于太阳系附近的年轻疏散星团Praesepe（M44）的金属丰度。
• 确定Praesepe与Hyades星团是否具有相同的化学组成，如先前假设的那样。
• 提高对通常受恒星活动与自转影响的年轻星团金属丰度测量的精度。
• 通过研究附近疏散星团的年龄分辨丰度模式，探究银河系盘的化学演化。
• 确立Praesepe目前作为太阳系附近最富金属的年轻疏散星团的地位。

提出的方法

• 利用TNG上的GIARPS光谱仪获取高分辨率、高信噪比的光学与近红外光谱。
• 采用严格差分（逐条谱线）光谱分析法，推导恒星参数与元素丰度。
• 以相同方法分析太阳光谱及Hyades的太阳类比星HD 28099，实现直接对比。
• 推导铁峰元素、α-元素及轻元素的丰度，并相对于铁进行归一化。
• 通过差分技术最小化内部不确定度，降低大气模型带来的系统误差。
• 分析中使用了全面的谱线列表，用于近红外波段的合成光谱拟合。

实验结果

研究问题

• RQ1 如一些近期研究所示，Praesepe是否比Hyades星团更富金属？
• RQ2 鉴于两者年龄相近，Praesepe与Hyades是否具有共同起源？
• RQ3 Praesepe的铁峰元素丰度精确值是多少？其与太阳系附近化学演化预期相比如何？
• RQ4 高精度差分光谱学能否解决关于年轻疏散星团金属丰度的争议？
• RQ5 Praesepe是否为太阳系附近最富金属的年轻疏散星团？

主要发现

• Praesepe的金属丰度为[Fe/H] = +0.21 ± 0.01 dex，显著高于Hyades星团。
• Praesepe与Hyades之间铁丰度的差异为Δ[Fe/H] = +0.05 ± 0.01 dex。
• 所有其他元素均与铁呈线性比例关系，表明化学丰度均匀演化。
• 该结果与Praesepe与Hyades起源于同一来源的假说相矛盾。
• Praesepe目前是太阳系附近最富金属的年轻疏散星团。
• 本研究证明了差分光谱学在实现对年轻活跃恒星高精度丰度测量方面的有效性。