The mass function of the Coma Berenices open cluster below 0.2 M⊙: a search for low-mass stellar and substellar members

Context. Little is known about the population of the Coma Berenices open cluster (age ∼500 Myr) below 0.2 M , and statistics show that there is a prominent deficit of very low-mass objects in this mass range compared to younger open clusters with ages of M > 0.14 M and α ∼ 0 in 0.14 > M > 0.06 M . Conclusions. Our analysis of the spectroscopy of 14 objects shows that they are very low-mass MV-dwarfs of spectral type and luminosity consistent with Coma open cluster membership. This suggests that the membership probability of our other candidates may be high. Our results suggest that the mass function of the Coma open cluster can be traced towards substellar objects, but comparison with a mass spectra of younger clusters indicates that the Coma open cluster has probably lost its lowest mass members by means of dynamical evolution.