在DES超微弱系统中搜寻天琴座RR型变星：Grus I、Kim 2、Phoenix II和Grus II
Search for RR Lyrae stars in DES ultra-faint systems: Grus I, Kim 2, Phoenix II, and Grus II
AI总结：
利用SOAR/Goodman和Blanco/DECam成像仪在四个DES超微弱星系中首次搜寻天琴座RR型变星，精确测定了Grus I和Phoenix II的距离模数，并发现Grus II前方可能存在一个更富金属的系统。
摘要：
本文利用SOAR/Goodman和Blanco/DECam成像仪，首次在暗能量巡天（DES）拍摄的四个超微弱系统中搜寻天琴座RR型变星（RRLs）。我们在Grus I天区探测到两个RRLs，Kim 2中无探测，Phoenix II中一个，Grus II中四个。通过探测这些恒星，我们精确测定了这些超微弱矮卫星星系的距离模数：Grus I的$μ_0$=20.51$\pm$0.10 mag（D$_{\odot}$=127$\pm$6 kpc），Phoenix II的$μ_0$=20.01$\pm$0.10 mag（D$_{\odot}$=100$\pm$5 kpc）。这些测量值大于Koposov等人2015年和Bechtol等人2015年的估计，意味着更大的物理尺度：Grus I增大5%，Phoenix II增大33%。对于Grus II，在探测到的四个RRLs中，一个与银河晕成员一致（D$_\odot$=24$\pm$1 kpc，$μ_0$=16.86$\pm$0.10 mag），另一个位于D$_\odot$=55$\pm$2 kpc（$μ_0$=18.71$\pm$0.10 mag），我们将其与Grus II关联，其余两个位于D$_\odot$=43$\pm$2 kpc（$μ_0$=18.17$\pm$0.10 mag）。此外，在Grus II的颜色-星等图中，与后两个RRLs相同亮度水平处出现微弱的红水平分支，且它们位于相同距离和区域，这表明一个更富金属的系统可能位于Grus II前方。最合理的场景是将这些恒星与Chenab/Orphan流关联。最后，我们对矮星系中RRLs的数量进行了全面且更新的分析。这使我们能够预测，利用两个或更多聚集的RRLs来发现新的超微弱矮星系的方法仅适用于亮度亮于M$_V\sim-6$ mag的系统。
英文摘要：
This work presents the first search for RR Lyrae stars (RRLs) in four of the ultra-faint systems imaged by the Dark Energy Survey (DES) using SOAR/Goodman and Blanco/DECam imagers. We have detected two RRLs in the field of Grus I, none in Kim 2, one in Phoenix II, and four in Grus II. With the detection of these stars, we accurately determine the distance moduli for these ultra-faint dwarf satellite galaxies; $μ_0$=20.51$\pm$0.10 mag (D$_{\odot}$=127$\pm$6 kpc) for Grus I and $μ_0$=20.01$\pm$0.10 mag (D$_{\odot}$=100$\pm$5 kpc) for Phoenix II. These measurements are larger than previous estimations by Koposov et al. 2015 and Bechtol et al. 2015, implying larger physical sizes; 5\% for Grus I and 33\% for Phoenix II. For Grus II, out of the four RRLs detected, one is consistent with being a member of the galactic halo (D$_\odot$=24$\pm$1 kpc, $μ_0$=16.86$\pm$0.10 mag), another is at D$_\odot$=55$\pm$2 kpc ($μ_0$=18.71$\pm$0.10 mag), which we associate with Grus II, and the two remaining at D$_\odot$=43$\pm$2 kpc ($μ_0$=18.17$\pm$0.10 mag). Moreover, the appearance of a subtle red horizontal branch in the color-magnitude diagram of Grus II at the same brightness level of the latter two RRLs, which are at the same distance and in the same region, suggests that a more metal-rich system may be located in front of Grus II. The most plausible scenario is the association of these stars with the Chenab/Orphan Stream. Finally, we performed a comprehensive and updated analysis of the number of RRLs in dwarf galaxies. This allows us to predict that the method of finding new ultra-faint dwarf galaxies by using two or more clumped RRLs will work only for systems brighter than M$_V\sim-6$ mag.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
