[论文解读] HST+IGRINS synergy to characterise the newly discovered metal-rich bulge globular cluster Patchick 126

Elisa R. Garro, Davide Massari+11 more|arXiv (Cornell University)|Jan 7, 2026

Stellar, planetary, and galactic studies被引用 0

一句话总结

本研究使用高分辨率近红外光谱（IGRINS）和深度 HST 光度测量来确认 Patchick 126 是一个金属富集、原位的银河系球状星团，并推导其金属性、α 元素增益、年龄、 reddening、距离和轨道。

ABSTRACT

We present the first comprehensive spectroscopic and deep photometric study of the globular cluster (GC) candidate Patchick~126. The spectroscopic analysis is based on high-resolution near-infrared data obtained with the IGRINS spectrograph, while the photometric analysis relies on HST observations from the Hubble Missing Globular Cluster Survey (MGCS). We derived abundances for $α$-(O, Mg, Si, Ca, Ti), light-(C, N), odd-Z (Na, Al), iron-peak (Fe, Co, Cr, Ni, Mn, V), and s-process elements (Ce) for four red giant stars observed in the H and K bands. Our results yield a mean metallicity of $\langle\mathrm{[Fe/H]} angle = -0.30\pm0.03$, with no evidence of intrinsic variation, and an $α$-enhancement of $\langle\mathrm{[α/Fe]} angle =+0.19\pm0.02$, consistent with the trends of metal-rich Galactic GCs. We detect an intrinsic C-N anti-correlation, but no Na-O or Al-Mg anti-correlations, in agreement with expectations for low-mass, metal-rich clusters. From the HST photometry, we constructed deep CMDs extending $\sim 2-3$ magnitudes below the MSTO. This depth allowed us to provide the first robust age estimate for the cluster. Applying the methods developed within the CARMA project, we derive an age of $11.9^{+0.3}_{-0.4}$~Gyr. We obtain a photometric metallicity of [Fe/H]$=-0.28$, in agreement with the spectroscopic results. The colour excess we derived, E(B-V) = 1.08, confirms that Patchick~126 is a heavily reddened cluster, located at a heliocentric distance of 7.8 kpc. From the orbital parameters, including energy, vertical angular momentum, circularity, and maximum vertical height, we find that Patchick~126 closely follows a disc-like orbit. Taken together, these results confirm that Patchick 126 is an in situ, low-mass globular cluster of the Milky Way, exhibiting properties that lie at the boundary between old-OCs and GCs.

研究动机与目标

• 通过获取一组元素的精确化学丰度来表征 Patchick 126。
• 确定星团的基本参数：金属性、α 增强、 reddening、距离和年龄。
• 评估星群内丰度变异性及多族群证据。
• 通过推导轨道并与银河成分比较，约束星团的起源。

提出的方法

• 使用 IGRINS 在 Gemini-South 上对四个红巨星成员获取高分辨率近红外光谱（H 和 K 波段）。
• 利用线深比与 Ti I/Ti II 电离平衡来推导恒星气氛参数（T_eff、log g、ξ_t）。
• 通过多条线目列表和 MARCS 模型大气，利用光谱合成法确定元素丰度（α、轻元素、奇数价、铁峰、s 过程）。
• 使用四种诊断方法（线轮廓拟合、核心线强度、拟合优度、EW 比较）来筛选最佳拟合丰度；将 χ^2 作为最终指示符。
• 以 Asplund 等人（2006）的太阳尺度为基准推断丰度，并通过改变 Teff、log g 和 ξ_t 来评估不确定性。

Figure 1: Colour-stacked image (red: F814W filter; blue: F606W filter; green: false colour from the average of the other two channels) of the central field of Patchick 126 covered by the Hubble MGCS ACS/WFC data.

实验结果

研究问题

• RQ1 Patchick 126 在 α、轻元素、奇数价、铁峰与 s 过程元素方面的详细化学丰度如何？
• RQ2 Patchick 126 与其他金属富集银河球状星团在化学上是否一致，是否显示多族群征兆？
• RQ3 结合光谱金属量与深度 HST 光度测量，星团的 reddening、距离和年龄是多少？
• RQ4 Patchick 126 的轨道是盘状原位轨道还是被捕获的起源？
• RQ5 丰度模式如何帮助将星团归类为球状星团与开放星团或其他系统？

主要发现

• 平均金属性 [Fe/H] = -0.30 ± 0.03，未发现内在变异的证据。
• 平均 α 元素增益 ⟨[α/Fe]⟩ = +0.19 ± 0.02（H 波段），以及 ⟨[Mg/Fe], [Si/Fe], [Ca/Fe], [Ti/Fe]⟩ ≈ +0.18 ± 0.06（K 波段）。
• 内在的 C–N 反相关被探测，平均 ⟨[N/Fe]⟩ = +0.17 ± 0.10 与 ⟨[C/Fe]⟩ = +0.15 ± 0.05；某些恒星在 N 上存在星-星变异。
• 从 HST CMD 在低于主序 Turn-off 的深度测得年龄约为 11.9^{+0.3}_{-0.4} Gyr（CARMA 方法）。
• CMDs 的光度金属量： [Fe/H] = -0.28，与光谱结果一致。
• Reddening E(B-V) = 1.08，日心距离 d = 7.8 kpc。
• 轨道参数指示是一个盘状原位轨道，能量、竖向角动量、圆度以及最大 |Z| 与内银河盘成员性一致。

Figure 2: Targets selection. (a) Gaia DR3 CMD for field stars selected within $\sim 3$ arcmin from the cluster centre (grey points) and for the high-probability proper-motion cluster members (black points). (b) Positions of the two samples shown in the (x, y) coordinates. The x-axis has been inverte