We present new WFC3/UVIS observations of UGC 4483, the closest example of a metal-poor blue compact dwarf galaxy, with a metallicity of $Z \simeq 1/15\ Z_{\odot}$ and located at a distance of $D \simeq 3.4$ Mpc. The extremely high quality of our new data allows us to clearly resolve the multiple stellar evolutionary phases populating the color-magnitude diagram (CMD), to reach more than 4 mag deeper than the tip of the red giant branch, and to detect for the first time core He-burning stars with masses $\lesssim 2$ M$_{\odot}$, populating the red clump and possibly the horizontal branch (HB) of the galaxy. By applying the synthetic CMD method to our observations, we determine an average star formation rate over the whole Hubble time of at least $(7.01\pm0.44) \times 10^{-4}$ $\mathrm{M_{\odot}/yr}$, corresponding to a total astrated stellar mass of $(9.60\pm0.61)\times 10^6$ $\mathrm{M_{\odot}}$, 87% of which went into stars at epochs earlier than 1 Gyr ago. With our star formation history recovery method we find the best fit with a distance modulus of DM = $27.45\pm0.10$, slightly lower than previous estimates. Finally, we find strong evidence of an old ($\gtrsim 10$ Gyr) stellar population in UGC 4483 thanks to the detection of an HB phase and the identification of six candidate RR Lyrae variable stars.
Ancient relic moderately metal-rich bulge cluster Tonantzintla 2
Università di Padova（帕多瓦大学）；Centro di Ateneo di Studi e Attività Spaziali “Giuseppe Colombo”（朱塞佩·科隆博大学中心太空研究与活动研究中心）；INAF-Osservatorio di Padova（意大利国家天体物理研究所帕多瓦天文台）；Max Planck Institute for Astronomy（马克斯·普朗克天文学研究所）；Universidade de São Paulo, IAG（圣保罗大学天文学、地球科学与 geodesy 学院）；Universidade Federal do Rio Grande do Sul（南里奥格兰德联邦大学）；Leibniz Institute for Astrophysics（莱布尼茨天体物理研究所）；Universidad Católica del Norte, Núcleo UCN en Arqueología Galáctica - Inst. de Astronomía（北天主教大学银河考古核心-天文学研究所）
Exploring the nature and synchronicity of early cluster formation in the Large Magellanic Cloud: II. Relative ages and distances for six ancient globular clusters
Public Release of A-SLOTH: Ancient Stars and Local Observables by Tracing Halos
半解析模型A-SLOTH（Ancient Stars and Local Observables by Tracing Halos）是第一个将第一批恒星和星系的形成与观测数据联系起来的公共代码。在几个成功的项目之后，我们发布了源代码，并在本文中描述了公共版本。该模型是基于暗物质合并树，可以生成的基础上扩展的Press-Schechter理论或可以从暗物质模拟导入。在这些合并树的顶部，A-SLOTH应用重子物理学的分析配方来模拟无金属和贫金属恒星的形成以及它们之间的过渡，具有前所未有的精度和保真度。A-SLOTH对单个恒星进行采样，包括辐射、化学和机械反馈。它是基于六个观测值，如汤姆逊散射的光学深度，银河系及其卫星星系的恒星质量，极端金属贫星的数量和宇宙恒星形成率密度在高红移校准。A-SLOTH具有中等计算要求的多用途应用。它可以用来限制第一恒星和高z星系的性质，预测银河系中最古老和最贫金属的恒星的性质，可以作为更大的宇宙学模拟的亚网格模型，并预测早期宇宙的下一代观测值，如超新星速率或引力波事件。
A pulsar escaping an ancient open cluster via tidal stripping
National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；Swinburne University of Technology（斯威本科技大学）；Tsinghua University（清华大学）；Sun Yat-sen University（中山大学）；University of Alberta（阿尔伯塔大学）；INAF – Astrophysics and Space Science Observatory of Bologna（意大利国家天体物理研究所博洛尼亚天文与空间科学观测站）
Discovery of Ancient Globular Cluster Candidates in the Relic, a Quiescent Galaxy at $z=2.5$
University of Massachusetts, Amherst（马萨诸塞大学阿默斯特分校）；Cosmic Dawn Center (DAWN)（宇宙黎明中心）；Department of Physics & Astronomy, Tufts University（塔夫茨大学物理与天文学系）；Ritter Astrophysical Research Center, University of Toledo（托莱多大学里特天体物理研究中心）；Department of Astrophysical Sciences, Princeton University（普林斯顿大学天体物理科学系）；Department of Physics, Ben-Gurion University of the Negev（内盖夫本-古里安大学物理系）；Department of Physics & Astronomy and PITT PACC, University of Pittsburgh（匹兹堡大学物理与天文学系及PITT PACC）；Centre for Astrophysics and Supercomputing, Swinburne University of Technology（斯威本科技大学天体物理与超级计算中心）
Extragalactic Planetary Nebulae (xPNe). Chemical evolution and assembly histories of nearby galaxies using Oxygen and Argon abundances. From the local universe to cosmic dawn
