Kinematics of the Ammonia Disk around the Protostar NGC 1333 IRAS 4A2

TL;DR

This study observes the ammonia emission around the protostar IRAS 4A2, revealing a Keplerian disk structure and estimating its properties, supporting models of low-mass star formation.

Contribution

First detailed kinematic analysis of ammonia disk around IRAS 4A2, confirming Keplerian rotation and estimating protostellar mass and age.

Findings

Disk radius of 130 AU with Keplerian rotation

Protostar mass estimated at 0.08 solar masses

Collapse age approximately 50,000 years

Abstract

The NGC 1333 IRAS 4A protobinary was observed in the ammonia (2, 2) and (3, 3) lines with an angular resolution of 0.3 arcsec. The ammonia emission source of IRAS 4A2 is elongated in the direction perpendicular to the bipolar jet and has a size of 0.55 arcsec or 130 AU. This emission structure was interpreted as a circumstellar disk around the IRAS 4A2 protostar, and the rotation kinematics of the disk was investigated by making a position-velocity diagram along the major axis. Assuming a Keplerian rotation, the disk has a rotation velocity of 1.8 km/s at a radius of 20 AU, which implies a central object of about 0.08 solar masses. The collapse age of the protostar is about 50,000 yr. The mass, accretion rate, and age are consistent with what are expected from the standard theory of low-mass star formation. If IRAS 4A2 grows at this rate, it may become a star similar to the Sun.