标题： NGC 205 中心的年轻恒星群体 显示英文标题

标题： The young stellar population at the center of NGC 205

摘要： 背景。 NGC 205 是一个特殊的矮椭球星系，其中心存在一群年轻的蓝色恒星。它们的起源仍然是争论的话题，中心的新鲜恒星形成活动可能与 NGC 205 和 M31 之间的动力学相互作用有关。 目的。 研究围绕 NGC 205 中心核球区域 30\arcsec （即$\sim$120 pc）内的恒星形成历史，以获得年轻恒星群体起源的线索。 方法。 通过将深场 HST/ACS CCD 光度测量与理论等年龄曲线和亮度函数进行比较，表征所研究区域的恒星组成，并计算近期恒星形成率。 结果。 我们的测光结果显示了一条以前未被探测到的年轻恒星的蓝色羽流，在 I$\simeq$26 以下清晰可辨。我们的分析表明，在大约 62 百万年前到 335 百万年前之间，NGC 205 内部区域产生了 1.9$\times10^5$ M$_\odot$太阳质量的恒星，最近的一次小规模爆发发生在约$\sim$25 百万年前。 这意味着在此期间恒星形成率为 $\sim7\times10^{-4}$ M$_\odot$/yr。 结论： 用一个恒定恒星形成率的模型得到的年轻主序星观测亮度函数的完美拟合，反驳了过去 $\sim$3亿年潮汐触发恒星形成活动的观点。 相反，恒星形成率恒定可能与NGC 205正处于首次与M 31相互作用一致。 显示英文摘要

摘要： Context. NGC 205 is a peculiar dwarf elliptical galaxy hosting in its center a population of young blue stars. Their origin is still matter of debate, the central fresh star formation activity possibly being related to dynamical interactions between NGC 205 and M31. Aims. The star formation history in the central 30\arcsec ($\sim$120 pc) around the NGC 205 central nucleus is investigated in order to obtain clues to the origin of the young stellar population. Methods. Deep HST/ACS CCD photometry is compared with theoretical isochrones and luminosity functions to characterize the stellar content of the region under study and compute the recent SF rate. Results. Our photometry reveals a previously undetected blue plume of young stars clearly distinguishable down to I$\simeq$26. Our analysis suggests that 1.9$\times10^5$ M$_\odot$ were produced between approximately 62 Myr and 335 Myr ago in the NGC 205 inner regions, with a latest minor episode occurring $\sim$25 Myr ago. This implies a star formation rate of $\sim7\times10^{-4}$ M$_\odot$/yr over this period. Conclusions. The excellent fit of the observed luminosity function of young main sequence stars obtained with a model having a constant star formation rate argues against a tidally triggered star formation activity over the last $\sim$300 Myr. Rather, a constant SF may be consistent with NGC 205 being on its first interaction with M 31.