Protostellar Evolution in Serpens Main: Possible Origin of Disk-Size
  Diversity
  We have observed the submillimeter continuum condensations SMM2, SMM4, SMM9,
and SMM11 in the star forming cluster Serpens Main using the Atacama Large
Millimeter/submillimeter Array during Cycle 3 in the 1.3 mm continuum, 12CO
J=2-1, SO J_N=6_5-5_4, and C18O J=2-1 lines at an angular resolution of ~0.55
(240 au). Sixteen sources have been detected in the 1.3 mm continuum, which can
be classified into three groups. Group 1 consists of six sources showing
extended continuum emission and bipolar/monopolar 12CO outflows. Although all
the Group 1 members are classified as Class 0 protostars, our observations
suggest evolutionary trends among them in terms of 12CO outflow dynamical time,
SO emission distribution, C18O fractional abundance, and continuum morphology.
Group 2 consists of four sources associated with a continuum filamentary
structure and no 12CO outflows. Central densities estimated from the 1.3 mm
continuum intensity suggest that they are prestellar sources in a marginally
Jeans unstable state. Group 3 consists of six Spitzer sources showing
point-like 1.3 mm continuum emission and clumpy 12CO outflows. These features
of Group 3 suggest envelope dissipation, preventing disk growth from the
present size, r <~ 60 au. The Group 3 members are protostars that may be
precursors to the T Tauri stars associated with small disks at tens-au radii
identified in recent surveys.
