2010ApJ...716..634G

We obtained JHK images and low-resolution JH spectra in the embedded young cluster in the Serpens cloud Main core (also known as Serpens North). We determined spectral types (SpT) for fifteen previously identified cluster members (the first time for five of them), one new candidate, and eleven stars that appear to be field interlopers. Extinction, for which we derived an analytical expression, was obtained by taking SpT and near-IR excess into account. The location on the Hertzsprung-Russell diagram indicates that we probed a low-mass population of the cloud (0.05-1.5 M_☉), including one to three brown dwarfs. We used our individually determined photospheric parameters to analyze the Infrared Space Observatory and the Spitzer determined spectral energy distribution (SED) classes. The latter were correlated with the age and location of the sources in the cloud. We find that most flat objects from our study (four out of five) have SEDs consistent with reddened classical T Tau stars; however, when comparing to the thick disk SEDs of lower mass M-type objects, we find that the flat ones show more excess, perhaps indicating an earlier evolutionary stage. We determined a median age for the cluster to be 1 Myr for distance of 380 pc, and 3 Myr for a less likely distance of 260 pc. The core of the cluster is on average younger than the rest of the cluster. We do not find objects with disks past 5 Myr. We do find diskless, X-ray bright objects younger than 1 Myr, as was also noted in the study of Winston et al. We find two groups of young objects associated with dark filaments, indicating that star formation was not always confined to the core.