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

¹ INAF – Istituto di Radioastronomia & Italian ALMA Regional Centre, Via P. Gobetti 101, 40129 Bologna, Italy
e-mail: brand@ira.inaf.it
² East Asian Observatory, 660 N. A’ohoku Place, University Park, Hilo, HI 96720, USA
³ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
⁴ Université Grenoble Alpes, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), 38401 Grenoble, France

Received: 18 April 2019
Accepted: 13 June 2019

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.

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.

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.

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⁻¹) 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⁻¹ pc⁻¹), 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 T_d ≈ 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 T_kin ≈ 21.4 K (68% credibility interval 14.5−35.5 K) and volume density n(H₂) ≈ 4.6 × 10⁵ cm⁻³ (8.3 × 10⁴−9.1 × 10⁵ cm⁻³). We have mapped the well-collimated large-scale outflow in ¹²CO(3–2). The outflow has a dynamical age of a few 10⁴ 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.