Probing the Protostellar Envelope around L1157: the Dust and Gas Connection

TL;DR

This study investigates the large-scale envelope of the Class 0 protostar L1157-mm using millimeter-wave observations, revealing a flattened, infalling structure that resembles a prestellar core rather than a disk.

Contribution

It provides detailed observational evidence and a simple model of the protostellar envelope, highlighting its morphology, kinematics, and early evolutionary stage.

Findings

Detected a large, flattened N2H+ envelope aligned perpendicular to the outflow.

Observed infall signatures and slow rotation in the envelope.

Identified the structure as a prestellar core-like envelope, not a disk.

Abstract

We present observations of the Class 0 protostar L1157-mm using the Combined Array for Research in Millimeter-wave Astronomy (CARMA) in 3 mm dust continuum and N2H+ line emission. In the N2H+ line, we detect a large-scale envelope extended over a linear size of ~20,000AU flattened in the direction perpendicular to the outflow. This N2H+ feature coincides with the outer envelope seen in the 8 micron extinction by Looney et al. Meanwhile, the dust continuum traces the compact, nearly spherical structure of the inner envelope, where N2H+ becomes depleted. This highly flattened N2H+ envelope also shows dynamical signatures consistent with gravitational infall in the inner region, but a slow, solid-body rotation at large scales. This flattened structure is not a rotationally supported circumstellar disk; instead, it resembles a prestellar core both morphologically and kinematically, representing the early phase of a Class 0 system. In this paper, we construct a simple model to interpret both the dust continuum and N2H+ emission and suggest a possible dynamical scenario for the overall properties of the envelope.