标题： Gemini-South和HST测光分析的球状星团NGC 6558。 银河系核球金属贫乏种群的年龄 显示英文标题

标题： Combined Gemini-South and HST photometric analysis of the globular cluster NGC 6558. The age of the metal-poor population of the Galactic Bulge

摘要： NGC 6558是一个低银纬球状星团，位于银河系核球方向。 由于高消光，该区域在推导准确参数方面存在挑战，这需要细致的测光分析。 我们展示了利用多历元高分辨率图像收集的近红外和光学测光数据的综合分析，这些数据来自Gemini-South/GSAOI+GeMS（在$J$和$K_S$滤镜下）以及HST/ACS（在F606W和F814W滤镜下）。 我们的目标是利用高质量的Gemini-South/GSAOI和HST/ACS测光数据来完善NGC 6558的基本参数。 此外，我们打算研究它在银河系核球形成中的作用。 我们研究了两种差分消光校正对年龄推导的影响。 当尽可能去除银河系核球场星的污染时，等时线拟合结合合成颜色-星等图给出了距离$8.41^{+0.11}_{-0.10}$kpc，年龄为$13.0\pm 0.9$Gyr，消光为 E($B-V$)$\,\,=0.34\pm0.02$，以及总选择性系数 R$_V = 3.2\pm0.2$，这是由于同时进行的近红外$-$光学合成颜色-星等图拟合。 轨道参数显示NGC~6558被限制在银河系内部，并且与棒状轨道不兼容，表明它是核球成员。 NGC~6558的古老年龄，结合相似的金属丰度和银河系核球中的蓝色水平分支，表明它是中等金属贫乏球状星团的一部分。 将旧的和中等贫金属 ([Fe/H]$\,\,\sim-1.1$) 星团组装在银河系核球中，我们推导了它们的年龄-金属丰度关系，恒星形成时间为$13.6\pm0.2$ Gyr 和有效产率 $\rho=0.007\pm0.009\,\, Z_\odot$，显示出比外源球状星团分支化学富集快十倍。 显示英文摘要

摘要： NGC~6558 is a low-galactic latitude globular cluster projected in the direction of the Galactic bulge. Due to high reddening, this region presents challenges in deriving accurate parameters, which require meticulous photometric analysis. We present a combined analysis of near-infrared and optical photometry from multi-epoch high-resolution images collected with Gemini-South/GSAOI+GeMS (in the $J$ and $K_S$ filters) and HST/ACS (in the F606W and F814W filters). We aim to refine the fundamental parameters of NGC~6558, utilizing high-quality Gemini-South/GSAOI and HST/ACS photometries. Additionally, we intend to investigate its role in the formation of the Galactic bulge. We studied the impact of two differential reddening corrections on the age derivation. When removing as much as possible the Galactic bulge field star contamination, the isochrone fitting combined with synthetic colour-magnitude diagrams gives a distance of $8.41^{+0.11}_{-0.10}$ kpc, an age of $13.0\pm 0.9$ Gyr, a reddening of E($B-V$)$\,\,=0.34\pm0.02$, and a total-to-selective coefficient R$_V = 3.2\pm0.2$ thanks to the simultaneous near-infrared$-$Optical synthetic colour-magnitude diagram fitting. The orbital parameters showed that NGC~6558 is confined whitin the inner Galaxy and it is not compatible with a bar-shape orbit, indicating that it is a bulge member. The old age of NGC~6558, combined with similar metallicity and a blue horizontal branch in the Galactic bulge, indicates that it is part of the moderately metal-poor globular clusters. Assembling the old and moderately metal-poor ([Fe/H]$\,\,\sim-1.1$) clusters in the Galactic bulge, we derived their age-metallicity relation with star formation stars at $13.6\pm0.2$ Gyr and effective yields of $\rho=0.007\pm0.009\,\, Z_\odot$ showing a chemical enrichment ten times faster than the ex-situ globular clusters branch.