CO DEPLET[ON IN THE STARLESS CLOUD CORE L1544

摘要

We present evidence for CO depletion toward the starless cloud core L1544. A comparison between C~17O and the 1.3 mm continuum dust emission shows that CO is depleted by a factor of ～10 at the dust peak. Our observations are consistent with a model in which CO is condensed out onto dust grains at densities above n_d ～10~5 cm~(-3). The corresponding radius of the "depleted region" is r_d ～ 6500 AU, and we find that this depletion causes 2.3 M_⊙ of gas to be lost to view in molecular line emission. Optically thin high-density tracers, such as HC~18O~+ and D~13CO~+, show double-peaked profiles which suggest that we are observing superposed emission from the foreground and background undepleted layers with density below n_d. We conclude from our data that the core is probably young (～10~4 yr old) and collapsing. For the component at V_LSR = 7.1 km s~(-1) in this line of sight, we estimate [DCO+]/[HCO+] = 0.12 ± 0.02, which is larger by a factor of order 2 than values derived in other dense cloud cores.