论文标题
搜索露天星团昏迷的锂锂耗竭边界
Search for the sub-stellar lithium depletion boundary in the open star cluster Coma Berenices
论文作者
论文摘要
我们主要旨在寻找露天星团昏迷的子星人群中的锂消耗边界（LDB）。我们使用以下大规模调查的最新公共发行版中的光学和红外光度合并了颜色和红外光度，对棕色矮人（BD）候选者进行了搜索：UKIRT/UKIRT/UKIDSS，PAN-STARRS，SDSSS和ALLWISE。我们使用$ Gaia $ dr2检查了与集群成员资格的Astrestric一致性。据报道，位于Coma Ber潮汐半径内的几十个新的候选BDS已报道，但没有一个比以前已知的成员明显淡淡，更凉爽。在10.4-m GTC上使用Osiris仪器进行光谱观测，在三个新的和五个先前已知的BD候选群集成员中搜索LI。在幅度范围j = 15--19和g = 20--23的八个昏迷目标中，在八个昏迷目标中的任何一个中都检测到6707.8 A的LII共振双线。光谱类型和径向速度源自GTC光谱。这些值证实了四个L2-L2.5矮人的簇成员资格，其中两个是文献中的新成员。在Coma Ber中的四个真正的BD成员中发现的大型LI耗竭因子意味着，LDB必须位于该集群中的L2.5的光谱类型。使用BDS的最新进化模型，设置了群集年龄的550 MYR。该约束已与其他约会方法结合使用，以获得昏迷的更新年龄估算为780美元$ \ pm $ 230 MYR。在Coma Ber中识别出明显凉爽的子星团成员，等待着欧几里得广泛的调查的出现，该调查的深度约为J = 23；这种出色的敏感性将使确定该集群中亚星LDB的精确位置并进行其子遗产人群的完整人口普查。
We mainly aim to search for the lithium depletion boundary (LDB) among the sub-stellar population of the open star cluster Coma Berenices. We carried out a search for brown dwarf (BD) candidates using colour-magnitude diagrams combining optical and infrared photometry from the latest public releases of the following large-scale surveys: UKIRT/UKIDSS, Pan-STARRS, SDSS, and AllWISE. We checked astrometric consistency with cluster membership using $Gaia$ DR2. A couple dozen new candidate BDs located inside the tidal radius of Coma Ber are reported, but none of these are significantly fainter and cooler than previously known members. A search for Li in three new and five previously known BD candidate cluster members was performed via spectroscopic observations using the OSIRIS instrument at the 10.4-m GTC. No LiI resonance doublet at 6707.8 A was detected in any of eight Coma Ber targets in the magnitude range J=15--19 and G=20--23 observed with the GTC. Spectral types and radial velocities were derived from the GTC spectra. These values confirm the cluster membership of four L2--L2.5 dwarfs, two of which are new in the literature. The large Li depletion factors found among the four bona fide BD members in Coma Ber implies that the LDB must be located at spectral type later than L2.5 in this cluster. Using the latest evolutionary models for BDs, a lower limit of 550 Myr on the cluster age is set. This constraint has been combined with other dating methods to obtain an updated age estimate of 780$\pm$230 Myr for the Coma Ber open cluster. Identification of significantly cooler sub-stellar cluster members in Coma Ber awaits the advent of the Euclid wide survey, which should reach a depth of about J=23; this superb sensitivity will make it possible to determine the precise location of the sub-stellar LDB in this cluster and to carry out a complete census of its sub-stellar population.
