A Census of Young Stars and Brown Dwarfs in IC 348 and NGC 1333

We have obtained optical and near-infrared spectra of candidate members of the star-forming clusters IC 348 and NGC 1333. We classify 100 and 42 candidates as new members of the clusters, respectively, which brings the total numbers of known members to 478 and 203. We also have performed spectroscopy on a large majority of the previously known members of NGC 1333 in order to provide spectral classifications that are measured with the same scheme that has been applied to IC 348 in previous studies. The new census of members is nearly complete for K _s < 16.8 at A _J < 1.5 in IC 348 and for K _s < 16.2 at A _J < 3 in NGC 1333, which correspond to masses of ≳0.01 M _⊙ for ages of 3 Myr according to theoretical evolutionary models. The faintest known members extend below these completeness limits and appear to have masses of ∼0.005 M _⊙. In extinction-limited samples of cluster members, NGC 1333 exhibits a higher abundance of objects at lower masses than IC 348. It would be surprising if the initial mass functions of these clusters differ significantly given their similar stellar densities and formation environments. Instead, it is possible that average extinctions are lower for less massive members of star-forming clusters, in which case extinction-limited samples could be biased in favor of low-mass objects in the more heavily embedded clusters like NGC 1333. In the Hertzsprung-Russell diagram, the median sequences of IC 348 and NGC 1333 coincide with each other for the adopted distances of 300 and 235 pc, which would suggest that they have similar ages. However, NGC 1333 is widely believed to be younger than IC 348 based on its higher abundance of disks and protostars and its greater obscuration. Errors in the adopted distances may be responsible for this discrepancy.

Based on data from the NASA Infrared Telescope Facility, Gemini Observatory, Canada-France-Hawaii Telescope, Keck Observatory, Subaru Telescope, the Digitized Sky Survey, and the Two Micron All-Sky Survey.