Shih-Yun Tang(Department of Physics, National Central University); W.~P. Chen(Graduate Institute of Astronomy, National Central University & Department of Physics, National Central University) P.~S. Chiang(Graduate Institute of Astronomy, National Cen
We have identified stellar and substellar member candidates in the nearby star cluster Coma Berenices, using the photometry and proper motions of 2MASS, UKIDSS, and URAT1. The candidates with Gaia DR1 parallax measurements provide the most reliable sample to constrain the distance, averaging 85.1pc with a dispersion 5.3pc, and age ~800Myr, of the cluster. This age is older than 400--600Myr commonly adopted in the literature. Alternatively, distance information was inferred from the spectral-energy distribution of an object, if photometric data at a sufficient number of bands were available. A total of 228 candidates were found, ranging from J ~ 3 to ~17.5 mag, corresponding to member masses 0.06--2.3 Msun, among which 134 should be members after field contamination is considered. This statistical sample shows a much shallower stellar mass function than in the field population in the solar neighborhood, peaking at about 0.3 Msun. A total of nine substellar candidates were found, six of which are known M-type objects in the literature. Our three new discoveries, confirmed by infrared spectroscopy, included an M8, an L1 and an L4 type members, extending from the previously known coolest members of late M types to even cooler members in the Coma Berenices star cluster.