Characterization of Stellar and Substellar Members in the Coma Berenices Star Cluster
Characterization of Stellar and Substellar Members in the Coma Berenices Star Cluster
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DOI：
10.3847/1538-4357/aacb7a
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发表时间：
2018-06
期刊：
影响因子：
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通讯作者：
S. Tang;W. P. Chen;P. Chiang;J. Jose;G. Herczeg;B. Goldman
中科院分区：
文献类型：
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作者：
S. Tang;W. P. Chen;P. Chiang;J. Jose;G. Herczeg;B. Goldman
我们已经确定了恒星和亚恒星成员在附近的星星集群后发座，使用测光，自行和距离的组合2 MASS，UKIDSS，URAT 1，盖亚/DR 2数据。盖亚/DR 2视差测量提供了最可靠的样本来限制距离，平均为86.7 pc，分散度为7.1 pc，年龄为1.8亿年。这一年龄比文献中通常采用的4亿至6亿年的年龄要大。我们的分析，在5°的集群半径内完成，导致192个候选人的身份，其中，场污染后，考虑到，约148个是真正的成员。这些成员的星等为J = 3.0等至17.5等，相当于恒星质量2.3-0.06 M。星系团的质量函数在0.3 M附近达到峰值，在的意义下，其中N是成员数，m是恒星质量，在0.3-2.3 M的质量范围内，斜率α = 0.49 ± 0.03。这比太阳附近的场密度要浅得多。斜率α = −1.69 ± 0.14，从0.3 M到0.06 M，这是我们样本中最小的质量。这个星系团是质量分离的，并且有一个向银河平面延伸的形状。我们的名单包含9个亚恒星成员，包括3个新发现的M8、L1和L4褐矮星，从之前已知的最冷的晚M型成员延伸到更冷的类型。
We have identified stellar and substellar members in the nearby star cluster Coma Berenices, using photometry, proper motions, and distances of a combination of 2MASS, UKIDSS, URAT1, and Gaia/DR2 data. Those with Gaia/DR2 parallax measurements provide the most reliable sample to constrain the distance, averaging 86.7 pc with a dispersion of 7.1 pc, and age of ∼800 Myr, of the cluster. This age is older than the 400–600 Myr commonly adopted in the literature. Our analysis, complete within 5° of the cluster radius, leads to identification of 192 candidates, among which, after field contamination is considered, about 148 are true members. The members have J ∼ 3 mag to ∼17.5 mag, corresponding to stellar masses 2.3–0.06 M☉. The mass function of the cluster peaks around 0.3 M☉, and in the sense of , where N is the number of members and m is stellar mass, with a slope α ≈ 0.49 ± 0.03 in the mass range 0.3–2.3 M☉. This is much shallower than that of the field population in the solar neighborhood. The slope α = −1.69 ± 0.14 from 0.3 M☉ to 0.06 M☉, the lowest mass in our sample. The cluster is mass-segregated and has a shape elongated toward the Galactic plane. Our list contains nine substellar members, including three new discoveries of an M8, an L1, and an L4 brown dwarfs, extending from the previously known coolest members of late-M types to even cooler types.