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

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 NH 3 , N 2 H + , HNC, HCO + , H 13 CO + , HCN and H 13 CN, 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 N 2 H + (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.

Star formation in Chamaeleon I and III: a molecular line study of the starless core population

“…Overall, the data show that Cha I is experiencing significantly lower star formation activity compared to other nearby clouds and our kinematical analysis so far suggests that only up to ∼28% of the Cha I starless cores might become prestellar in the future. Morales Ortiz et al (2012) also found that almost all the starless cores in the Vela-D molecular cloud are not virialized or gravitationally bound. Overall, they estimated that approximately 30% of the whole core population in Vela-D is gravitationally bound, which is comparable to the number of cores in Cha I that will likely become unstable in the future.…”

Revealing the dynamics of Class 0 protostellar discs with ALMA

“…For 13 CO and C 18 O we used relative abundances of 1.3 × 10 −6 and 1.8 × 10 −7 , respectively (Wilson & Rood 1994). For N2H + we have adopted a fiducial value of 3 × 10 −10 (Caselli et al 2002;Jørgensen et al 2004;Tafalla et al 2004;Beuther & Henning 2009;Johnstone et al 2010;Morales Ortiz et al 2012;Tsitali et al 2015) and for HCO + a value of 1 × 10 −9 (Jørgensen et al 2004;Sandell & Wright 2010;Morales Ortiz et al 2012;Zernickel et al 2012). For the relative abundance of H 13 CO + we have taken the abundance of HCO + scaled down by a factor of 77 typical for the ratio of 12 C to 13 C in the local interstellar medium (Wilson & Rood 1994).…”