The Distinct Evolutionary Nature of Two Class 0 Protostars in Serpens Main SMM4

Abstract

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, 12 CO J = 2 − 1, SO J N = 6 5 − 5 4 , and C 18 O 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 12 CO 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 α ∼ 40 • , respectively. The SO emission traces shocked regions, such as cavity walls of outflows and the vicinity of SMM4B. The C 18 O emission mainly traces an infalling and rotating envelope around SMM4B. The C 18 O 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.

Protostellar Evolution in Serpens Main: Possible Origin of Disk-size Diversity

“…We observed five regions, highlighted by the cyan circles in Figure 1, in Serpens Main using ALMA in Cycle 3 on 2016 May 19 and 21. The results of the SMM11 and SMM4 condensations were reported in Aso et al (2017a) and Aso et al (2018), respectively. This paper reports comprehensive results including all the detected sources.…”

“…Names, coordinates, and Classes of the 1.3 mm sources detected with our ALMA observations. The bolometric luminosity L bol , bolometric temperature T bol , and evolutionary class are cited from Dunham et al (2015); Aso et al (2017aAso et al ( , 2018 outflows as seen in Figure 2c. Note that the SO emission from SMM4A and that from SMM4B in Figure 2c(i) are distinct from each other because of the different velocity ranges (Aso et al 2018).…”

“…The bolometric luminosity L bol , bolometric temperature T bol , and evolutionary class are cited from Dunham et al (2015); Aso et al (2017aAso et al ( , 2018 outflows as seen in Figure 2c. Note that the SO emission from SMM4A and that from SMM4B in Figure 2c(i) are distinct from each other because of the different velocity ranges (Aso et al 2018). The SO emission appears to surround the 12 CO outflows or lies in the outer parts of the 12 CO outflow in SMM4A, SMM4B, S68N, and S68Nc1, suggesting that SO traces cavity walls of these 12 CO outflows.…”

“…The presence of the 12 CO outflows (Figure 2b) indicates star formation activities in the Group 1 members. In fact, those except S68Nb1 and S68Nc1 are identified as Class 0 protostars from their SEDs (Dunham et al 2015;Aso et al 2017aAso et al , 2018. Hence, the SEDs of S68Nb1 and S68Nc1 are examined to reveal their evolutionary stages in this subsection.…”

“…In addition, one Class 0 protostar was identified in SMM11 by recent observations using CARMA ) and ALMA (Aso et al 2017a) at millimeter wavelengths. The ALMA observations also identified two other Class 0 protostars, SMM4A and SMM4B, revealing a ∼500 au sized disk around SMM4A (Aso et al 2018). JCMT observations found several 12 CO out-flows over the entire region of Serpens Main (Davis et al 1999).…”