标题： B59致密核的年龄、恒星含量和恒星形成时间尺度 显示英文标题

标题： The Age, Stellar Content and Star Formation Timescale of the B59 Dense Core

摘要： 我们利用NASA红外望远镜设施上的SpeX光谱仪获得的中等分辨率近红外光谱，来表征巴纳德59（B59）的恒星构成，B59是管状星云中最活跃的恒星形成核心。 通过对20个候选年轻恒星（YSO）的光谱中亮度和温度敏感特征进行测量，我们识别出可能的背景巨星，并测定了每颗恒星的光谱类型、消光值以及近红外连续光谱的过量。 我们发现B59由晚期型（K4-M6）低质量（0.9--0.1太阳质量）的YSO组成，其恒星的中位年龄与Rho Oph、金牛座和Chameleon恒星形成区内的YSO的年龄相当，甚至略大。 通过采用D'Antona等人计算的主序前模型推导绝对年龄估计，并仅考虑统计不确定性，我们测得B59的中位恒星年龄为2.6±0.8百万年。 如果包括潜在的系统性效应，B59的中位恒星年龄（DM98）的误差预算增加到2.6+4.1/-2.6百万年。 我们还发现，基于主序前演化轨道得出的相对年龄排序取决于所采样的恒星质量范围，因为模型等时线具有显著不同的质量依赖性。 我们为B59测得的最大似然中位恒星年龄以及该区域观测到的气体性质表明，B59的致密核在大约6个动力学时间尺度内稳定，未发生整体坍缩，并且正在以每个动力学时间约6%的恒星形成效率积极地形成恒星。 这一最大似然值与最近包含各种反坍塌支持形式（如次临界磁场、喷流和原恒星加热的辐射反馈）的恒星形成模拟结果非常一致。 [摘要] 显示英文摘要

摘要： We have used moderate resolution, near-infrared spectra from the SpeX spectrograph on the NASA Infrared Telescope facility to characterize the stellar content of Barnard 59 (B59), the most active star-forming core in the Pipe Nebula. Measuring luminosity and temperature sensitive features in the spectra of 20 candidate YSOs, we identified likely background giant stars and measured each star's spectral type, extinction, and NIR continuum excess. We find that B59 is composed of late type (K4-M6) low-mass (0.9--0.1 M_sun) YSOs whose median stellar age is comparable to, if not slightly older than, that of YSOs within the Rho Oph, Taurus, and Chameleon star forming regions. Deriving absolute age estimates from pre-main sequence models computed by D'Antona et al., and accounting only for statistical uncertainties, we measure B59's median stellar age to be 2.6+/-0.8 Myrs. Including potential systematic effects increases the error budget for B59's median (DM98) stellar age to 2.6+4.1/-2.6 Myrs. We also find that the relative age orderings implied by pre-main sequence evolutionary tracks depend on the range of stellar masses sampled, as model isochrones possess significantly different mass dependencies. The maximum likelihood median stellar age we measure for B59, and the region's observed gas properties, suggest that the B59 dense core has been stable against global collapse for roughly 6 dynamical timescales, and is actively forming stars with a star formation efficiency per dynamical time of ~6%. This maximum likelihood value agrees well with recent star formation simulations that incorporate various forms of support against collapse, such as sub-critical magnetic fields, outflows, and radiative feedback from protostellar heating. [abridged]