A spectral line survey of the starless and proto-stellar cores detected by BLAST toward the Vela-D molecular cloud^⋆,⋆⋆

¹ UJF-Grenoble 1 / CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, 38041 Grenoble, France
e-mail: jorge.luis379@gmail.com
² Osservatorio Astrofisico di Arcetri – INAF, Largo E. Fermi 5, 50125 Firenze, Italy
³ University of Puerto Rico, Rio Piedras Campus, Physics Department, Box 23343, UPR station, San Juan, Puerto Rico, USA
⁴ School of Physics, University of New South Wales, Sydney NSW 2052, Australia
⁵ LERMA-LRA, UMR 8112 du CNRS, Observatoire de Paris, École Normale Supérieure, UPMC & UCP, 24 rue Lhomond, 75231 Paris Cedex 05, France
⁶ Istituto di Fisica dello Spazio Interplanetario – INAF, via Fosso del Cavaliere 100, 00133 Roma, Italy
⁷ Osservatorio Astronomico di Roma – INAF, via Frascati 33, 00040 Monteporzio Catone, Roma, Italy
⁸ Dipartimento di Fisica, Universitá del Salento, CP 193, 73100 Lecce, Italy

Received: 18 January 2012
Accepted: 23 April 2012

Abstract

Context. Starless cores represent a very early stage of the star formation process, before collapse results in the formation of a central protostar or a multiple system of protostars.

Aims. We use spectral line observations of a sample of cold dust cores, previously detected with the BLAST telescope in the Vela-D molecular cloud, to perform a more accurate physical and kinematical analysis of the sources.

Methods. We present a 3-mm and 1.3-cm survey conducted with the Mopra 22-m and Parkes 64-m radio telescopes of a sample of 40 cold dust cores, including both starless and proto-stellar sources. 20 objects were also mapped using molecular tracers of dense gas. To trace the dense gas we used the molecular species NH₃, N₂H⁺, HNC, HCO⁺, H¹³CO⁺, HCN and H¹³CN, where some of them trace the more quiescent gas, while others are sensitive to more dynamical processes.

Results. The selected cores have a wide variety of morphological types and also show physical and chemical variations, which may be associated to different evolutionary phases. We find evidence of systematic motions in both starless and proto-stellar cores and we detect line wings in many of the proto-stellar cores. Our observations probe linear distances in the sources  ≳ 0.1   pc, and are thus sensitive mainly to molecular gas in the envelope of the cores. In this region we do find that, for example, the radial profile of the N₂H⁺(1−0) emission falls off more quickly than that of C-bearing molecules such as HNC(1−0), HCO⁺(1−0) and HCN(1−0). We also analyze the correlation between several physical and chemical parameters and the dynamics of the cores.

Conclusions. Depending on the assumptions made to estimate the virial mass, we find that many starless cores have masses below the self-gravitating threshold, whereas most of the proto-stellar cores have masses which are near or above the self-gravitating critical value. An analysis of the median properties of the starless and proto-stellar cores suggests that the transition from the pre- to the proto-stellar phase is relatively fast, leaving the core envelopes with almost unchanged physical parameters.