The L723 low-mass star forming protostellar system: Resolving a double core

Abstract

We present 1.35mm Submillimeter Array (SMA) observations around the low-mass Class 0 source IRAS 19156+1906, at the center of the LDN 723 (L723) dark cloud. We detected emission from dust as well as emission from H 2CO 30,3-20,2, DCN 3-2, and CN 2-1 lines, which arise from two cores, SMA1 and SMA2, separated by 29 (880AU in projected distance). SMA2 is associated with the previously detected source VLA2. Weak SiO 5-4 emission is detected, possibly tracing a region of interaction between the dense envelope and the outflow. We modeled the dust and H2CO emission from the two cores. The results from the modeling show that the cores have similar physical properties (density and temperature distribution) but that SMA2 has a larger p-H2CO abundance (by a factor of 3-10) than SMA1. The p-H2CO abundances' findings are compatible with the value of the outer part of the circumstellar envelopes associated with Class 0 sources. SMA2 is harboring an active multiple low-mass protostellar system and powering at least one molecular outflow. In contrast, there are no known signs of outflow activity toward SMA1. This suggests that SMA2 is more evolved than SMA1. The kinematics of the two sources show marginal evidence of infall and rotation motions. The mass detected by the SMAobservation, which trace scales of ≲1000AU, is only a small fraction of the mass contained in the large-scale molecular envelope, which suggests that L723 is still in a very early phase of star formation. Despite the apparent quiescent nature of the L723, fragmentation is occurring at the center of the cloud at different scales. Thus, at ≃1000AU, the cloud has fragmented in two cores: SMA1 and SMA2. At the same time, at least one of these cores, SMA2, has undergone additional fragmentation at scales of ≃150AU, forming a multiple stellar system. © 2009. The American Astronomical Society.