大麦哲伦云中三个球状星团研究表明中红外天琴座RR型变星周期-光度关系与金属丰度无关
The independence of the mid-infrared RR Lyrae Period-Luminosity relation from metallicity from a study of three globular clusters in the Large Magellanic Cloud
- Department of Physics, University of Bath（巴斯大学物理系）
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中文总结 AI 辅助
本研究利用斯皮策数据研究大麦哲伦云中三个球状星团，证实中红外天琴座RR型变星周期-光度关系与金属丰度无关，并给出可靠距离模数。
中文摘要 AI 辅助
天琴座RR型变星是追踪年老（>10 Gyr）恒星族的脉动变星，表现出强烈的中红外周期-光度（PL）关系，可利用已知视差进行校准以推断距离。本文展示了大麦哲伦云中三个孤立球状星团——Reticulum、NGC 1841和NGC 1466——的周期-光度关系和距离模数。我们的分析使用了卡内基天琴座RR型变星项目获得的遗产斯皮策太空望远镜图像，以及一个内部自洽的、仅限于RRab星的样本，其星团成员资格通过盖亚DR3自行和测光确认。在斯皮策3.6微米波段，我们使用从银河系球状星团推导的斜率同时拟合这些星团的PL，得到消光校正后的距离模数：Reticulum为18.47±0.09等，NGC 1841为18.29±0.09等，NGC 1466为18.61±0.09等。后两者是这些星团首次基于天琴座RR型变星PL的距离模数，且三者均与其他技术的文献值一致。此外，我们将斜率作为自由参数拟合PL，发现这种源自LMC的PL与源自银河系球状星团的PL一致。同时拟合这三个星团的PLZ，得到金属丰度系数c=-0.03±0.05等dex⁻¹，可视为PL对金属丰度的依赖性可忽略不计（|c|<0.1等dex⁻¹）。对PL/PLZ的内在宽度W建模，得到一致的值W≈0.1±0.02等，表明内在宽度并非由金属丰度驱动。
英文摘要
RR Lyrae are pulsating variable stars tracing old ($>10$ Gyr) stellar populations, and exhibit a strong mid-infrared Period-Luminosity (PL) relation that can be calibrated with known parallaxes to infer distances. Here we present Period-Luminosity relations and distance moduli for three isolated globular clusters in the Large Magellanic Cloud: Reticulum, NGC 1841, and NGC 1466. Our analysis uses legacy \textit{Spitzer Space Telescope} images obtained by the Carnegie RR Lyrae Program, and an internally self-consistent sample restricted to RRab stars, with cluster membership confirmed using Gaia DR3 proper motions and photometry. In the Spitzer 3.6~$μ$m band, we simultaneously fit a PL for these clusters using a slope derived from Galactic Globular Clusters, yielding extinction-corrected distance moduli of $18.47\pm0.09$ mag for Reticulum, $18.29\pm0.09$ mag for NGC 1841, and $18.61\pm0.09$ mag for NGC 1466. The latter two are the first RR Lyrae PL-based distance moduli for these clusters, and all three are consistent with literature values from other techniques. Additionally we fit a PL with slope as a free parameter, and find that this LMC-derived PL is consistent with that derived from Galactic GCs. Simultaneously fitting a PLZ for the three clusters yields a metallicity coefficient $c= -0.03\pm0.05~\mathrm{mag}~\mathrm{dex}^{-1}$ which can be considered a negligible dependence of the PL on metallicity ($|c| <0.1$ mag dex$^{-1}$). Modelling an intrinsic width, $W$, to the PL/ PLZ yields a consistent value $W\approx0.1\pm0.02~\mathrm{mag}$, suggesting intrinsic width is not driven by metallicity.
