Properties of the Youngest Protostars in Perseus, Serpens, and Ophiuchus

TL;DR

This study provides a comprehensive analysis of the youngest protostars in Perseus, Serpens, and Ophiuchus, revealing episodic accretion and estimating protostellar lifetimes through multi-wavelength observations and modeling.

Contribution

It offers the first unbiased census of embedded protostars in these clouds, combining extensive surveys with evolutionary modeling to understand accretion processes and protostellar lifetimes.

Findings

Identification of 39 Class 0 and 89 Class I sources.

Evidence for episodic accretion during the Class I phase.

Estimated Class 0 lifetime of approximately 1.7 x 10^5 years.

Abstract

We present an unbiased census of deeply embedded protostars in Perseus, Serpens, and Ophiuchus, assembled by combining large-scale 1.1 mm Bolocam continuum and Spitzer Legacy surveys. We identify protostellar candidates based on their mid-infrared properties, correlate their positions with 1.1 mm core positions, and construct well-sampled SEDs using our extensive wavelength coverage (lam=1.25-1100 micron). Source classification based on the bolometric temperature yields a total of 39 Class 0 and 89 Class I sources in the three cloud sample. We compare to protostellar evolutionary models using the bolometric temperature-luminosity diagram, finding a population of low luminosity Class I sources that are inconsistent with constant or monotonically decreasing mass accretion rates. This result argues strongly for episodic accretion during the Class I phase, with more than 50% of sources in a ``sub-Shu'' (dM/dt < 1e-6 Msun/yr) accretion state. Average spectra are compared to protostellar radiative transfer models, which match the observed spectra fairly well in Stage 0, but predict too much near-IR and too little mid-IR flux in Stage I. Finally, the relative number of Class 0 and Class I sources are used to estimate the lifetime of the Class 0 phase; the three cloud average yields a Class 0 lifetime of 1.7e5 yr, ruling out an extremely rapid early accretion phase. Correcting photometry for extinction results in a somewhat shorter lifetime (1.1e5 yr). In Ophiuchus, however, we find very few Class 0 sources (N(Class0)/N(ClassI)=0.1-0.2), similar to previous studies of that cloud. The observations suggest a consistent picture of nearly constant average accretion rate through the entire embedded phase, with accretion becoming episodic by at least the Class I stage, and possibly earlier.