ALMA Observations of SMM11 Reveal an Extremely Young Protostar in Serpens Main Cluster

Abstract

We report the discovery of an extremely young protostar, SMM11, located in the associated submillimeter condensation in the Serpens Main cluster using the Atacama Large Millimeter/submillimeter Array (ALMA) during its Cycle 3 at 1.3 mm and an angular resolution of ∼ 0\buildrel{\prime\prime}\over{.} 5∼ 210 {AU}. SMM11 is a Class 0 protostar without any counterpart at 70 μm or shorter wavelengths. The ALMA observations show 1.3 mm continuum emission associated with a collimated ¹²CO bipolar outflow. Spitzer and Herschel data show that SMM11 is extremely cold ({T}_{bol} = 26 K) and faint ({L}_{bol} ≲ 0.9 {L}_⊙ ). We estimate the inclination angle of the outflow to be ∼ 80^\circ , almost parallel to the plane of the sky, from simple fitting using a wind-driven-shell model. The continuum visibilities consist of Gaussian and power-law components, suggesting a spherical envelope with a radius of ∼600 au around the protostar. The estimated low C¹⁸O abundance, X(C¹⁸O) = 1.5-3 × {10}^-10, is also consistent with its youth. The high outflow velocity, a few 10 {km} {{{s}}}^-1 at a few 1000 au, is much higher than theoretical simulations of first hydrostatic cores, and we suggest that SMM11 is a transitional object right after the second collapse of the first core.