C18O and C17O Observations of Embedded Young Stars in the Taurus Molecular Cloud. I. Integrated Intensities and Column Densities

We report on the results of a survey of C 18 O and C 17 O toward the 20 most deeply embedded young stars in the Taurus molecular cloud. Most of the sources have been observed in both the J = 1-0 and J = 2-1 transitions of each species. The analysis shows that in general the C 17 O emission is optically thin, whereas the C 18 O emission has optical depths between 0.5 and 1.0. The material traced by these lines has an excitation temperature of ~8 K and column density ranging from 3 to 42 × 10 21 cm -2 . The column density toward a source is found to be inversely correlated with the source's bolometric temperature, T bol . The correlation between T bol and source age is reexamined, and the new correlation is used to find the rate at which mass is removed from the circumstellar environment of these sources. We find that the outflows observed toward the sources and infall with a constant mass accretion rate typical of a 10-20 K singular isothermal sphere are individually unlikely to produce the observed reduction in mass over the class I phase. However, a scenario where a highly efficient outflow dominates the beam mass loss during the first 3 × 10 4 yr and then standard infall dominates the beam mass loss thereafter is plausible.