Abstract
Context. Studies of Class 0 objects allow to characterize the dynamical processes taking place at the onset of the star formation process and to determine the physical mechanisms responsible for the outcome of the collapse. Observations of dense gas tracers allow for the characterization of key kinematics of the gas that are directly involved in the star formation process, such as infall, outflow, and rotation. Aims. This work is aimed at investigating the molecular line velocity profiles of the Class 0 protostellar object B335 and attempts to place constraints on the infall motions happening in the circumstellar gas of the object. Methods. We present observations of C17O (1–0), C18O (1–0), and 12CO (2–1) transitions along with an analysis of spectral profiles at envelope radii between 100 and 860 au. Results. C17O emission presents a double-peaked line profile distributed in a complex velocity field. Both peaks present an offset of 0.2–1 km s−1 from the systemic velocity of the source in the probed area. The optical depth of the C17O emission has been estimated and found to be less than 1, suggesting that the two velocity peaks trace two distinct velocity components of the gas in the inner envelope. Conclusions. After discarding possible motions that could produce the complex velocity pattern, such as rotation and outflow, we conclude that infall motions are responsible for producing the velocity field. Because inside-out symmetric collapse cannot explain those observed profiles, it is suggested that these are produced by non-isotropic accretion from the envelope into the central source along the outflow cavity walls.
Highlights
Low-mass stars are known to form in dense molecular gas clouds
This work is aimed at investigating the molecular line velocity profiles of the Class 0 protostellar object B335 and attempts to place constraints on the infall motions happening in the circumstellar gas of the object
Summary In this work, we describe ALMA observations of the C17O emission tracing gas kinematics in the B335 envelope and we show that the line emission exhibits widespread doublepeaked profiles
Summary
Low-mass stars are known to form in dense molecular gas clouds. Class 0 objects represent the first stage of the star formation process, when most of the mass is still contained in the envelope surrounding the protostar (André et al 1993; André 1995). Models of protostellar collapse (Shu et al 1987) suggest that it is during this phase that the circumstellar gas is transported to the central object thanks to accretion processes During this stage, angular momentum needs to be removed from the envelope and stored in the central object or dissipated through viscous processes to allow for the formation of the star. The accretion mode, the rate at which it happens, and the duration of possible accretion episodes during this phase will determine the final stellar mass (André 1995; Basu & Jones 2004; Bate & Bonnell 2005; Myers 2012) Studying this phase is crucial, as it allows us to understand what the kinematics and dynamics of the gas are at the onset of collapse and to determine how those affect the outcome of the star formation process
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