The Evolutionary State of Stars in the NGC 1333S Star Formation Region

Abstract

We present 2 μm near-IR spectroscopic observations of a sample of 33 objects in the NGC 1333S active star-forming cluster centered on the pre–main-sequence star SSV 13. We have previously studied this region photometrically in the optical and near-IR, and with the addition of these near-IR spectra, we further probe the pre–main-sequence cluster membership and evolutionary state. From the atomic and molecular absorption features observed, together with the earlier photometry, we derive spectral types, effective temperatures, masses, and ages of the stars and conclude that almost all (90%) the stars observed in this sample are pre–main-sequence objects. This result significantly refines the evolutionary information obtained from photometric evidence alone. Comparison with theoretical evolutionary tracks and isochrones suggests that our survey has sampled sources with masses in the range 0.2–2 M⊙ and stellar ages between 7 × 104 and 1 × 108 yr with a preponderance of sources around 3 × 106 yr. This implies the presence of low- to intermediate-mass T Tauri stars of evolutionary designation Class I to Class III. We conclude that star formation seems to have occurred in likely several bursts rather than occurring coevally. Star formation in such a region as NGC 1333S is likely significantly affected by the large number of active molecular outflows in the region, which could provide a mechanism for cloud turbulence and the onset of subsequent star formation.