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Published February 20, 2009 | Published
Journal Article Open

Properties of the youngest protostars in Perseus, Serpens, and Ophiuchus


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 (mid-IR) properties, correlate their positions with 1.1 mm core positions from Enoch et al. in 2006 and 2007, and Young et al. in 2006, and construct well-sampled spectral energy distributions using our extensive wavelength coverage (λ = 1.25-1100 μm). 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 < 10^(–6) M_☉ yr^(–1)) 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 is used to estimate the lifetime of the Class 0 phase; the three-cloud average yields a Class 0 lifetime of 1.7 ± 0.3 × 10^5 yr, ruling out an extremely rapid early accretion phase. Correcting photometry for extinction results in a somewhat shorter lifetime (1.1 × 10^5 yr). In Ophiuchus, however, we find very few Class 0 sources (N_Class 0/N_Class I ~ 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.

Additional Information

© 2009 American Astronomical Society. Print publication: Issue 2 (2009 February 20) Received 2008 July 24; accepted for publication 2008 September 23; published 2009 February 23. The authors thank J. Hatchell and Y. Shirley, and the anonymous referee for comments and suggestions that helped to improve this paper, and M. Dunham for many fruitful discussions. We are grateful to B. Whitney for sharing the protostellar evolutionary model data used here.We thank the Lorentz Center in Leiden for hosting meetings that contributed to this paper. Part of the work was done while in residence at the Kavli Institute for Theoretical Physics in Santa Barbara, California. Support for this work, part of the Spitzer Legacy Science Program, was provided by NASA through contracts 1224608 and 1230782 issued by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407. Additional support was provided by NASA through the Spitzer Space Telescope Fellowship Program and obtained from NASA Origins Grants NNG04GG24G and NNX07AJ72G to theUniversity of Texas at Austin. Support for the development of Bolocam was provided by NSF grants AST-9980846 and AST-0206158.

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