A multi-molecular line study of the star-forming globule CB88-230

Abstract

Context. This paper relates to low-mass star formation in globules, and the interaction of newly-formed stars with their environment. We follow up on the results of our earlier observations of this globule. <BR /> Aims: Our aim is to study the gas- and dust environment of the young stellar object (YSO) in globule CB88 230, the large-scale molecular outflow triggered by the jet driven by the YSO, and their interaction. <BR /> Methods: We carried out submillimetre continuum and multi-line molecular observations with several single-dish facilities, mapping the core of the globule and the large-scale outflow associated with the YSO. <BR /> Results: Dust continuum and molecular line maps (of 12CO, C18O, CS, CH3OH) show a flattened (axes ratio 1.5-1.7), asymmetric core with a full width at half maximum (FWHM)-diameter of 0.16-0.21 pc. Line profiles of 12CO, 13CO(2-1, 3-2), and CS(2-1) show self-absorption near the YSO; the absorption dip is at a slightly ( 0.3 km/s) redder velocity than that of the quiescent gas, possibly indicating infall of cooler envelope gas. The mass of the core, determined from C18O(1-0) observations, is about 8 M☉, while the virial mass is in the range 5-8M☉, depending on the assumed density distribution. We detect a slight velocity gradient ( 0.98 km/s/pc), though rotational energy is negligible with respect to gravitational and turbulent energy of the core. A fit to the spectral energy distribution of the core gives a dust temperature Td ≈ 18 K and a gas mass of ca. 2 M☉ (assuming a gas-to-dust ratio of 100). More careful modelling of the sub-mm emission (not dominated by the relatively hot central regions) yields M ≈ 8M☉. From the molecular line observations we derive gas temperatures of 10-20 K. A Bayesian analysis of the emission of selected molecules observed towards the YSO, yields Tkin ≈ 21.4 K (68% credibility interval 14.5-35.5 K) and volume density n(H2) ≈ 4.6 × 10^5 cm^-3 (8.3 × 10^4 - 9.1 × 10^5 cm^-3). We have mapped the well-collimated large-scale outflow in 12CO(3-2). The outflow has a dynamical age of a few 10^4 yr, and contains little mass (a few 10^-2 M☉). A misalignment between the axis of this large-scale outflow and that of the hot jet close to the YSO indicates that the outflow direction may be changing with time.