We present new WFC3/UVIS observations of UGC4483, the closest example of a metal-poor blue compact dwarf galaxy, with a metallicity of Z≃1/15 Z _⊙ and located at a distance of D≃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 ≲2 M _⊙, 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 , corresponding to a total astrated stellar mass of M _⊙, 87% of which went into stars at epochs earlier than 1Gyr ago. With our star formation history recovery method we find the best fit with a distance modulus of DM=27.450.10, slightly lower than previous estimates. Finally, we find strong evidence of an old (≳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.

我们展示了 UGC4483 的新 WFC3/UVIS 观测结果，UGC4483 是最接近的贫金属蓝致密矮星系的例子，其金属丰度为Z ≃1/15 Z _⊙，位于距离D ≃3.4 Mpc。我们的新数据质量极高，使我们能够清楚地解析色星图 (CMD) 中的多个恒星演化阶段，达到比红巨星分支尖端深 4 等的位置，并首次探测到质量 ≲2 M _{⊙ 的}时间核心 He 燃烧恒星，分布在红团和可能的星系水平分支 (HB) 中。通过将合成 CMD 方法应用于我们的观测，我们确定了整个哈勃时间的平均恒星形成率至少为 , 对应于 M _⊙的总星体质量，其中 87% 在早于 1Gyr 的纪元进入恒星。使用我们的恒星形成历史恢复方法，我们找到了距离模数 DM=27.450.10 的最佳拟合，略低于之前的估计。最后，我们在 UGC 4483 中发现了一个古老（≳ 10 Gyr）恒星群的有力证据，这要归功于检测到 HB 阶段和六颗候选天琴座 RR 变星。