Star formation in Perseus - II. SEDs, classification, and lifetimes

Context. Hatchell et al. (2005, A&A, 440, 151) (Paper I) published a submillimetre continuum map of the Perseus molecular cloud, detecting the starless and protostellar cores within it. Aims. To determine the evolutionary stage of each submm core in Perseus, and investigate the lifetimes of these phases. Methods. We compile spectral energy distributions (SEDs) from 2MASS (1-2 mu m), Spitzer IRAC (3.6, 4.5, 5.8, 8.0 mu m), Michelle (11 and 18 mu m), IRAS (12, 25, 60, 100 mu m), SCUBA (450 and 850 mu m) and Bolocam (1100 mu m) data. Sources are classified star-less/protostellar on the basis of infrared and/or outflow detections and Class I/Class 0 on the basis of T-bol, L-bol/L-smm and F-3.6/F-850. In order to investigate the dependence of these evolutionary indicators on mass, we construct radiative transfer models of Class 0 sources. Results. Of the submm cores, 56/103 (54%) are confirmed protostars on the basis of infrared emission or molecular outflows. Of these, 22 are classified Class 1 on the basis of three evolutionary indicators, 34 are Class 0, and the remaining 47 are assumed starless. Perseus contains a much greater fraction of Class 0 sources than either Taurus or Rho Oph. We derive estimates for the correlation between bolometric luminosity and envelope mass for Class I and Class 0 sources. Conclusions. Comparing the protostellar with the T Tauri population, the lifetime of the protostellar phase in Perseus is 0.25-0.67 Myr (95% confidence limits). The relative lifetime of the Class 0 and Class 1 phases are similar, confirming the results of Visser et al. (2002, AJ, 124, 2756) in isolated cores. We find that for the same source geometry but different masses, evolutionary indicators such as Tbol vary their value. It is therefore not always appropriate to use a fixed threshold to separate Class 0 and Class I sources. More modelling is required to determine the observational characteristics of the Class 0/Class I boundary over a range of masses.