Physical structure of the envelopes of intermediate-mass protostars

¹ Laboratoire d'Astrophysique de l'Observatoire de Grenoble, BP 53, 38041 Grenoble Cedex 9, France e-mail: ncrimier@obs.ujf-grenoble.fr
² Observatorio Astronómico Nacional (OAN, IGN), Apdo 112, 28803 Alcalá de Henares, Spain
³ School of Physics & Astronomy, E.C. Stoner Building, The University of Leeds, Leeds LS2 9JT, UK
⁴ National Research Council of Canada, Herzberg Institute of Astrophysics, 5071, West Saanich Road, Victoria, BC, V9E 2E7, Canada
⁵ Department of Physics & Astronomy, University of Victoria, Victoria, BC, V8P 1A1, Canada
⁶ Department of Physics and Astronomy, University of Calgary, Calgary, T2N 1N4, AB, Canada
⁷ Centro de Astrobiología (CSIC/INTA), Laboratory of Molecular Astrophysics, Ctra. Ajalvir km. 4, 28850 Torrejón de Ardoz, Spain
⁸ Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands
⁹ Max-Planck-Institut fur Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

Received: 19 October 2009
Accepted: 27 March 2010

Abstract

Context. Intermediate mass protostars provide a bridge between low- and high-mass protostars. Furthermore, they are an important component of the UV interstellar radiation field. Despite their relevance, little is known about their formation process.

Aims. We present a systematic study of the physical structure of five intermediate mass, candidate Class 0 protostars. Our two goals are to shed light on the first phase of intermediate mass star formation and to compare these protostars with low- and high-mass sources.

Methods. We derived the dust and gas temperature and density profiles of the sample. We analysed all existing continuum data on each source and modelled the resulting SED with the 1D radiative transfer code DUSTY. The gas temperature was then predicted by means of a modified version of the code CHT96.

Results. We found that the density profiles of five out of six studied intermediate mass envelopes are consistent with the predictions of the “inside-out” collapse theory. We compared several physical parameters, like the power law index of the density profile, the size, the mass, the average density, the density at 1000 AU and the density at 10 K of the envelopes of low-, intermediate, and high-mass protostars. When considering these various physical parameters, the transition between the three groups appears smooth, suggesting that the formation processes and triggers do not substantially differ.