The Circumstellar Structure and Excitation Effects around the Massive Protostar Cepheus A HW 2

TL;DR

This study uses high-resolution SMA and VLA observations to reveal a disk-like structure and complex gas features around the massive protostar Cepheus A HW 2, indicating a physically connected disk-protostar-jet system.

Contribution

It provides detailed high-resolution imaging of the circumstellar environment of Cepheus A HW 2, clarifying the structure and excitation effects around this massive protostar.

Findings

Detection of a 450 AU elongated disk structure around HW 2.

Identification of two ammonia cores with signs of heating.

Evidence supporting a disk-protostar-jet system rather than chance superposition.

Abstract

We report SMA 335 GHz continuum observations with angular resolution of ~0.''3, together with VLA ammonia observations with ~1'' resolution toward Cep A HW 2. We find that the flattened disk structure of the dust emission observed by Patel et al. is preserved at the 0.''3 scale, showing an elongated structure of ~$0.''6 size (450 AU) peaking on HW 2. In addition, two ammonia cores are observed, one associated with a hot-core previously reported, and an elongated core with a double peak separated by ~1.''3 and with signs of heating at the inner edges of the gas facing HW 2. The double-peaked ammonia structure, as well as the double-peaked CH3CN structure reported previously (and proposed to be two independent hot-cores), surround both the dust emission as well as the double-peaked SO2 disk structure found by Jimenez-Serra et al. All these results argue against the interpretation of the elongated dust-gas structure as due to a chance-superposition of different cores; instead, they imply that it is physically related to the central massive object within a disk-protostar-jet system.