The molecular condensations ahead of Herbig-Haro objects

I. Multi-transition observations of HH 2

¹ Departament d'Astronomia i Meteorologia, Universitat de Barcelona, Av. Diagonal 647, 08028 Barcelona, Catalunya, Spain
² Department of Physics and Astronomy, University College London, London, WC1E 6BT, England, UK
³ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

Corresponding author: J. M. Girart, jgirart@am.ub.es

Received: 27 December 2001
Accepted: 4 April 2002

Abstract

We present a CSO and BIMA molecular line survey of the dense, quiescent molecular environment ahead of HH 2. The molecular gas is cold, 13 K, and moderately dense, 3 cm^-3. A total of 14 species has been detected (including different isotopes and deuterated species). The relative abundances of the clump are compared with other dense molecular environments, including quiescent dark clouds, and active low and high mass star forming regions. This comparison confirms the peculiar chemical composition of the quiescent gas irradiated by the HH objects. Thus, from this comparison, we found that the HCO⁺, CH₃OH and H₂CO are strongly enhanced. SO and SO₂ are weakly enhanced, whereas HCN and CS are underabundant. The CN abundance is within the range of values found in starless dark clouds, but it is low with respect to high mass star forming regions. Finally, the chemical composition of HH 2 confirms the qualitative results of the Viti & Williams (1999) complex chemical model that follows the chemical behavior of a molecular clump irradiated by a HH object.