标题： 一种评估麦哲伦云年轻恒星聚团中前主序星年龄和年龄分布的新方法 显示英文标题

标题： A New Method for the Assessment of Age and Age-Spread of Pre-Main Sequence Stars in Young Stellar Associations of the Magellanic Clouds

摘要： 我们提出了一种新的方法，用于评估麦哲伦云中恒星形成区域内前主序（PMS）星的年龄和年龄弥散，同时考虑了测光误差、不可分解的双星性、消光差异、恒星变异性、吸积以及拥挤效应。 该方法的应用通过使用PMS演化模型构建合成颜色-亮度图实现。 我们通过应用上述偏差将每个等时线转换为人工PMS恒星在CMD中的二维概率分布，这些偏差会使这些恒星偏离其原始CMD位置。 然后采用最大似然技术推导出每个观测到的恒星具有特定年龄的概率，以及整个星团的最佳年龄。 我们基于哈勃太空望远镜/先进巡天相机对麦哲伦星云中的年轻星协LH 95进行的最深成像，将该方法应用于约2000个PMS恒星的测光目录中，其检测极限为V~28，对应于M~0.2太阳质量。 我们的分析表明，年龄确定对所考虑的演化模型网格和假设的双星分数非常敏感。 根据这些因素，LH 95的年龄被发现从2.8百万年变化到4.4百万年。 我们的分析允许我们区分真实的年龄弥散和由物理和观测偏差引起的表观CMD展宽。 我们发现LH 95的年龄弥散可以用高斯分布很好地表示，FWHM约为2.8百万年至4.2百万年，这取决于模型和双星分数。 我们检测到系统平均年龄与恒星质量之间存在依赖关系。 这种依赖似乎没有物理意义，而是由于PMS演化模型的不完善，这些模型倾向于预测中间质量恒星较低的年龄和低质量恒星较高的年龄。 显示英文摘要

摘要： We present a new method for the evaluation of the age and age-spread among pre-main-sequence (PMS) stars in star-forming regions in the Magellanic Clouds, accounting simultaneously for photometric errors, unresolved binarity, differential extinction, stellar variability, accretion and crowding. The application of the method is performed with the statistical construction of synthetic color-magnitude diagrams using PMS evolutionary models. We convert each isochrone into 2D probability distributions of artificial PMS stars in the CMD by applying the aforementioned biases that dislocate these stars from their original CMD positions. A maximum-likelihood technique is then applied to derive the probability for each observed star to have a certain age, as well as the best age for the entire cluster. We apply our method to the photometric catalog of ~2000 PMS stars in the young association LH 95 in the LMC, based on the deepest HST/ACS imaging ever performed toward this galaxy, with a detection limit of V~28, corresponding to M~0.2 Msun. Our treatment shows that the age determination is very sensitive to the considered grid of evolutionary models and the assumed binary fraction. The age of LH 95 is found to vary from 2.8 Myr to 4.4 Myr, depending on these factors. Our analysis allows us to disentangle a real age-spread from the apparent CMD-broadening caused by the physical and observational biases. We find that LH 95 hosts an age-spread well represented by a gaussian distribution with a FWHM of the order of 2.8 Myr to 4.2 Myr depending on the model and binary fraction. We detect a dependence of the average age of the system with stellar mass. This dependence does not appear to have any physical meaning, being rather due to imperfections of the PMS evolutionary models, which tend to predict lower ages for the intermediate masses, and higher ages for low-mass stars.