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

Abstract

Aims. We aim to study the composition and energetics of the circumstellar material of DK Cha, an intermediate-mass star in transition from an embedded configuration to a star plus disk stage, during this pivotal stage of its evolution. Methods. Using the range scan mode of PACS on the Herschel Space Observatory, we obtained a spectrum of DK Cha from 55 to 210 μm as part of the DIGIT key program. Results. 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 J_(K−1 K+1) = 7_(07) (E_u/k = 843 K), and OH lines up to E_u/k = 290 K were detected. Conclusions. The continuum emission in our PACS SED scan matches the flux expected by a model consisting of a star, a surrounding disk of 0.03 M_⊙, 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 may be photon-heated, but some emission may be caused by C-shocks in the walls of the outflow cavity.

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