Characterization of Stellar and Substellar Members in the Coma Berenices
  Star Cluster
  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 {\it Gaia}/DR2 data. Those with {\it
Gaia}/DR2 parallax measurements provide the most reliable sample to constrain
the distance, averaging 86.7~pc with a dispersion 7.1~pc, and the age
$\sim800$~Myr, of the cluster. This age is older than the 400--600~Myr commonly
adopted in the literature. Our analysis, complete within 5deg 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
$J\sim3$~mag to $\sim17.5$~mag, corresponding to stellar masses
2.3--0.06~$M_\odot$. The mass function of the cluster peaks around
0.3~$M_\odot$ and, in the sense of $dN/dm = m^{-\alpha}$, where $N$ is the
number of members and $m$ is stellar mass, has a slope $\alpha\approx
0.49\pm0.03$ in the mass range 0.3--2.3~$M_\odot$. This is much shallower than
that of the field population in the solar neighborhood. The slope
$\alpha=-1.69\pm0.14$ from 0.3~$M_\odot$ to 0.06~$M_\odot$, 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.
