Title: Young Substellar Objects in NGC 1333
Author(s): Yumiko Oasa, Munechika Tanaka, and Yoichi Itoh
Abstract:


We present the results of a deep near-infrared (NIR) photometric survey searching for very low mass young stellar objects (YSOs) in the embedded cluster and the subsequent NIR spectroscopy and IR multi-wavelength photometry for them.
Our JHK photometric survey covers an area of ~5�f �~ 5�f in the NGC1333 region.
Based on NIR color?color diagrams, embedded YSO candidates were identified using NIR excesses. Approximately half of them exhibit extremely low luminosity, indicating very low mass. Combining the reddening-corrected luminosity with theoretical evolutionary models, the low-luminosity YSO candidates are considered to be young substellar-mass objects. Furthermore, some sources could have planetary masses. The subsequent NIR spectroscopic observations of some young substellar object candidates using the Subaru telescope demonstrate that they have low effective temperatures consistent with those of young brown dwarfs. Their location on the HR diagram indicates that some are very young and have substellar mass in spite of uncertainties of temperature determination and evolutionary models for young substellar objects.
In addition, we have conducted the L-band photometry of some YSO candidates with IRTF and UKIRT. It reveals the presence of circumstellar disks around young subsltellar objects.
We also argue that the fraction of substellar objects is larger than those in other young clusters and the mass function of the YSO candidates appears to be increasing toward the substellar-mass regime, similar to that of dust clumps. It implies that substellar-mass distributions may depend on the initial conditions of the molecular cloud.