标题： 在银河系疏散星团中寻找UVdim恒星 来自紫外线测光的线索 显示英文标题

标题： Hunting for UVdim stars in Galactic Open clusters. Clues from ultraviolet photometry

摘要： 分裂的主序星（MSs）和扩展的主序转折（eMSTOs）已在几乎所有年龄小于2 Gyr的麦哲伦云星团中被观测到。 最近，哈勃空间望远镜（HST）的紫外测光在五个年龄介于40至200 Myr之间的麦哲伦云星团以及一个1.5 Gyr的星团中发现了一种令人困惑的新恒星群体，称为UVdim。 这些UVdim恒星主要位于蓝色主序星上，该主序星由慢速旋转体组成，它们独特的紫外特性被认为源自尘埃周围的原行星盘。 尽管eMSTOs在麦哲伦云和年龄相近的银河系开放星团（OCs）中都很常见，但UVdim恒星尚未在银河系OCs中进行过研究。 在这项工作中，我们通过结合Swift/UVOT、SkyMapper和Gaia测光数据，将寻找UVdim恒星的范围扩展到了35个年龄小于2 Gyr的银河系开放星团。 通过构建类似于HST WFC3/UVIS所使用的颜色-颜色图，我们发现在大多数银河系开放星团中没有UVdim类似恒星的证据，并且仅在五个系统中识别出可能的UVdim候选者。 年轻OCs中UVdim恒星的稀有性表明麦哲伦云星团与其银河系对应体之间可能存在差异，尽管其根本原因尚不清楚。 显示英文摘要

摘要： Split main-sequences (MSs) and extended main-sequence turn-offs (eMSTOs) have been observed in nearly all Magellanic Clouds clusters younger than 2 Gyr. More recently, Hubble Space Telescope (HST) ultraviolet photometry uncovered a puzzling new population of UV-absorbed stars, dubbed UVdim, in five Magellanic Clouds clusters aged between 40 and 200 Myr, as well as in one 1.5 Gyr-old cluster. These UVdim stars predominantly lie on the blue MS, which is composed of slow rotators, and their distinct UV properties are believed to stem from dusty circumstellar disks. Although eMSTOs are common in both Magellanic Clouds and Galactic open clusters (OCs) of comparable ages, UVdim stars have not yet been investigated in Galactic OCs. In this work, we fill that gap by combining Swift/UVOT, SkyMapper, and Gaia photometry to extend the search for UVdim stars to 35 Galactic OCs younger than 2 Gyr. By constructing colour-colour diagrams analogous to those employed with HST WFC3/UVIS, we find no evidence of UVdim-like stars in most Galactic open clusters and identify possible UVdim candidates in only five systems. The rarity of UVdim stars in young OCs suggests a potential difference between Magellanic Cloud clusters and their Milky Way counterparts, although the underlying reason remains unclear.