ENVELOPE STRUCTURE OF DEEPLY EMBEDDED YOUNG STELLAR OBJECTS IN THE SERPENS MOLECULAR CLOUD

摘要

Aperture-synthesis and single-dish (sub-) millimeter molecular-line and continuum observations reveal in great detail the envelope structure of deeply embedded young stellar objects (SMM 1 = FIRS 1, SMM 2, SMM 3, SMM 4) in the densely star-forming Serpens Molecular Cloud. SMM 1, 3, and 4 show partially resolved (>2" = 800 AU) continuum emission in the beam of the Owens Valley Millimeter Array at #lambda# =3.4-l.4 mm. The continuum visibilities accurately constrain the density structure in the envelopes, which can be described by a radial power law with slope -2.0 +- 0.5 on scales of 300 to 8000 AU. Inferred envelope masses within a radius of 8000 AU are 8.7, 3.0, and 5.3 solar mass for SMM 1, 3, and 4, respectively. A point source with 20-30 of the total flux at 1.1 mm is required to fit the observations on long baselines, corresponding to warm envelope material within ~ 100 AU or a circumstellar disk. No continuum emission is detected interferometrically toward SMM 2, corresponding to an upper limit of 0.2 solar mass assuming T_d = 24 K. The lack of any compact dust emission suggests that the SMM 2 core does not contain a central protostar. Aperture-synthesis observations of the ~13CO, C~18O, HCO~+, H~13CO~+, HCN, H~13CN, N_2H~~+ 1-0, SiO 2-1, and SO 2_2-1 transitions reveal compact emission toward SMM 1, 3, and 4. SMM 2 shows only a number of clumps scattered throughout the primary field of view, supporting the conclusion that this core does not contain a central star. The compact molecular emission around SMM 1, 3, and 4 traces 5"-10" (2000-4000 AU) diameter cores tha