Dust, Ice and Gas in Time (DIGIT) Herschel program first results: A full PACS-SED scan of the gas line emission in protostar DK Cha

TL;DR

This study uses Herschel PACS data to analyze the gas, dust, and molecular composition of the intermediate-mass protostar DK Cha, revealing detailed molecular line emissions and the influence of outflows on its circumstellar environment.

Contribution

First full PACS-SED scan of gas line emission in DK Cha, providing detailed molecular and atomic line data and modeling the circumstellar structure during star formation.

Findings

Detected over 50 molecular and atomic lines, including extensive CO, water, and OH lines.

The continuum matches a star-disk-envelope model, indicating the object is emerging from main accretion.

Evidence of outflow influence and possible shock heating in the circumstellar environment.

Abstract

DK Cha is an intermediate-mass star in transition from an embedded configuration to a star plus disk stage. We aim to study the composition and energetics of the circumstellar material during this pivotal stage. Using the Range Scan mode of PACS on the Herschel Space Observatory, we obtained a spectrum of DK Cha from 55 to 210 micron as part of the DIGIT Key Program. Almost 50 molecular and atomic lines were detected, many more than the 7 lines detected in ISO-LWS. Nearly the entire ladder of CO from J=14-13 to 38-37 (E_u/k = 4080 K), water from levels as excited as E_u/k = 843 K, and OH lines up to E_u/k = 290 K were detected. The continuum emission in our PACS SED scan matches the flux expected from a model consisting of a star, a surrounding disk of 0.03 Solar mass, and an envelope of a similar mass, supporting the suggestion that the object is emerging from its main accretion stage. Molecular, atomic, and ionic emission lines in the far-infrared reveal the outflow's influence on the envelope. The inferred hot gas can be photon-heated, but some emission could be due to C-shocks in the walls of the outflow cavity.