Evidence for transient clumps and gas chemical evolution in the CS core of L673

¹ Department of Physics, The Ohio State University, 174 West 18th Avenue, Columbus, OH 43210, USA e-mail: omorata@mps.ohio-state.edu
² Departament d'Astronomia i Meteorologia, Universitat de Barcelona, Av. Diagonal 647, 08028 Barcelona, Catalunya, Spain
³ Institut de Ciències de l'Espai (CSIC) / IEEC, Gran Capità 2, 08034 Barcelona, Catalunya, Spain

Received: 10 August 2004
Accepted: 10 December 2004

Abstract

We present FCRAO maps as well as combined BIMA and FCRAO maps of the high density molecular emission towards the CS core in the L673 region. With the FCRAO telescope we mapped the emission in the CS (), C³⁴S (), HCO⁺ (), and H¹³CO⁺ () lines. The high-density molecular emission, which arises from a filamentary structure oriented in the NW-SE direction, shows clear morphological differences for each molecule. We find that HCO⁺ has an extremely high optical depth, and that the H¹³CO⁺ emission is well correlated with submm sources. The BIMA and FCRAO combined maps recover emission from structure previously undetected or marginally detected, and show an overall aspect of a filamentary structure connecting several intense clumps. We found a total 15 clumps in our combined data cube, all of them resolved at our angular resolution, with diameters in the 0.03–0.09 pc range. Their estimated masses range between 0.02 and 0.2 , except for the largest clump, which has a mass of ~1.2 . We find a clear segregation between the northern and southern region of the map: the northern section shows the less chemically evolved gas and less massive but more numerous clumps, while the southern region is dominated by the largest and most massive clump, and contains the more evolved gas, as traced by emission of late-time molecules. We find that the derived clump masses are below the virial mass, and that the clump masses become closer to the virial mass when they get bigger and more massive. This supports the idea that these clumps must be transient, and that only the more massive ones are able to condense into stars. The clumps we detect are probably in an earlier evolutionary stage than the “starless cores” reported recently in the literature. Only the most massive one has properties similar to a “starless core”.