The Distinct Evolutionary Nature of two Class 0 Protostars in Serpens
  Main SMM4
  We have observed the submillimeter continuum condensation SMM4 in Serpens
Main using the Atacama Large Millimeter/submillimeter Array (ALMA) during its
Cycle 3 in 1.3 mm continuum, 12CO J=2-1, SO J_N=6_5-5_4, and C18O J=2-1 lines
at angular resolutions of ~0.55" (240 au). The 1.3 mm continuum emission shows
that SMM4 is spatially resolved into two protostars embedded in the same core:
SMM4A showing a high brightness temperature, 18 K, with little extended
structure and SMM4B showing a low brightness temperature, 2 K, with compact and
extended structures. Their separation is ~2100 au. Analysis of the continuum
visibilities reveals a disk-like structure with a sharp edge at r~240 au in
SMM4A, and a compact component with a radius of 56 au in SMM4B. The 12CO
emission traces fan-shaped and collimated outflows associated with SMM4A and
SMM4B, respectively. The blue and red lobes of the SMM4B outflow have different
position angles by ~30 deg. Their inclination and bending angles in the 3D
space are estimated at i_b~ 36 deg, i_r~70 deg, and alpha~40 deg, respectively.
The SO emission traces shocked regions, such as cavity walls of outflows and
the vicinity of SMM4B. The C18O emission mainly traces an infalling and
rotating envelope around SMM4B. The C18O fractional abundance in SMM4B is ~50
times smaller than that of the interstellar medium. These results suggest that
SMM4A is more evolved than SMM4B. Our studies in Serpens Main demonstrate that
continuum and line observations at millimeter wavelengths allow us to
differentiate evolutionary phases of protostars within the Class 0 phase.
