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 during its Cycle 3 in 1.3 mm continuum, ¹²CO J = 2-1, SO J _N = 6₅-5₄, 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°. Their inclination and bending angles in the 3D space are estimated at i _b ∼ 36°, i _r ∼ 70°, and ∼ 40°, 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.