A C18O (J=1-0) SURVEY OF PROTOSTELLAR CANDIDATES EMBEDDED IN THE TAURUS MOLECULAR CLOUD

(CO)-O-18 (J = 1-0) observations were made toward a sample of 32 proto stellar sources associated with the Taurus molecular cloud complex. Th e sources were selected from the IRAS Point Source Catalog with criter ia to pick up solar-type protostar candidates. The (CO)-O-18 intensity for the optically invisible objects is correlated with the IRAS flux at 25, 60, and 100 mum, while at 12 mum the correlation is rather ambi guous. The correlation between the (CO)-O-18 intensity and the IRAS fl ux for the invisible objects suggests that both the (CO)-O-18 intensit y and the IRAS flux at 25, 60, and 100 mum well represent the amount o f gas and dust, respectively, in the extended envelopes (radius approx imately 400-4000 AU) around these objects, while the worse correlation seen at 12 mum is consistent with the 12 mum emission arising from co mpact circumstellar disks. The visible objects show wide scatter in th e (CO)-O-18 intensity with no clear correlation with the IRAS flux at all four wavelength bands, consistent with the IRAS emission originati ng from circumstellar disks at any infrared wavelengths. The differenc e in the correlation between the invisible and visible sources means t hat protostellar envelopes around invisible sources are dissipated awa y in the course of evolution from invisible sources into visible ones, probably due to accretion onto the central star or due to being blown off by molecular outflows. The observed smooth decrease of the (CO)-O -18 intensity from the invisible to visible sources implies the mass d issipation timescale of approximately 10(5) yr at a rate of greater-th an-or-similar-to 6 x 10(-7) M. yr-1.