Astron. Astrophys. 350, 659-671 (1999)

6. Conclusions

The intermediate-mass star forming site located in the globule CB3 has been investigated through a multiline survey at mm-wavelenghts, observing emission due to the CO, CS, H¹³CO⁺, SiO, CH₃OH, SO, SO₂, H₂S, OCS and H₂CO molecular species, and probing a wide range of physical conditions. The main results are the following:

1. In CB3, at least two YSOs are located, CB3-NIR and CB3-mm, which is probably a Class 0 object. The present CO observations have allowed to show that CB3-mm is the driving source of a bipolar outflow, which reveals different clumps along the main axis, suggesting that episodic increases of the mass loss process have occurred. Moreover, the CB3 outflow shows a remarkable emission due to several transitions of the observed molecular species, indicating that it belongs to the class of the chemically active ones.

2. The CO outflow has a typical excitation temperature of 15-20 K, and it is quite massive (4 ) and very powerful, since the momentum is 37.2 km s^-1, the kinetic energy is 5.5 10⁴⁵ ergs and the mechanical luminosity is 5.6 . The dynamical flow parameters and the analysis of the CO velocity profiles place the CB3 outflow close to others driven by 10²-10³ sources like, e.g., HH7-11 or NGC2071.

3. The outflow structure is clearly detectable already at low velocity ( 1-2 km s^-1) with respect to the ambient one, suggesting that the bulk of the CO emission comes from gas interacting with the mass loss process. Moreover, the outflow kinetic energy represents the 26% of the gravitational selfbinding energy of the clump hosting CB3-mm indicating that the outflow is able to affect the structure of CB3, clearing a significant amount of the high-density gas where the star forming process has occurred.

4. H¹³CO⁺ and CS observations reveal a molecular clump with size of 0.19 pc around CB3-mm. Moreover, the CS profiles show a self-absorption feature with always a brighter blue peak and a fainter red peak, consistent with the presence of infall motions. This makes of CB3-mm a good candidate for being a Class 0 source, in agreement with previous submillimetre observations.

5. The observations of tracers of the high-velocity outflow component such as CH₃OH and SiO allow to clearly detect the jet-like outflow structure, with a collimation factor 7. The two molecular species are present only along the main outflow axis, whose emission is represented by broad ( 8-10 km s^-1) profiles, confirming the enhancement of their abundances in young molecular outflows. In particular, the SiO data clearly demonstrate that CB3-mm is the outflow driving source, pointing out four clumps, whose size is less than 0.1 pc. At least two episodic mass losses have been detected: the more distant clumps are 10⁵ yr old, while the age of the clumps near CB3-mm is about 10⁴ yr. Thus, we found the indication that CB3 is in a relatively evolved evolutionary stage.

6. The three observed SO lines exhibit different profiles: while the 2₂-1₁ transition shows narrow linewidths (1-2 km s^-1) and trace the ambient clump, the 4₃-3₂ and 6₅-5₄ lines are broad ( 10 km s^-1) and are able to trace the outflow, revealing its clumps. Moreover, the emission of other S-bearing molecules such as SO₂, H₂S and OCS, as well as that due to H₂CO, is definitely enhanced in the outflow.

7. By means of statistical-equilibrium calculations, using a LVG code, physical parameters of the molecular gas traced by SiO and SO have been obtained. Moreover, for CH₃OH the rotation diagram method as well as line ratios have been used. We infer quite high densities, close to 10⁵-10⁶ cm^-3, and the indication that SO is tracing gas at lower density with respect to SiO and CH₃OH. The total column densities of the molecular species along the outflow axis have been derived: 5-8 10¹⁶ cm^-2 (CO), 10¹⁶ cm^-2 (CH₃OH), 3 10¹⁴ cm^-2 (H₂CO), 10¹⁴ cm^-2 (SO, SO₂, OCS), 5 10¹³-2 10¹⁴ cm^-2 (H₂S), 5-8 10¹³ cm^-2 (CS), 10¹³ cm^-2 (SiO) and 10¹² cm^-2 (H¹³CO⁺).

8. Different molecular species trace different high-density components of the system composed by the molecular clump connected with star formation and the high-velocity gas of the outflow. The SiO molecule traces the highest velocity jet-like mass loss process, pointing out the inner part of the outflow. On the other hand, SO and CH₃OH play an intermediate role between SiO and CO, since they seem to be associated with more extended regions produced by the interaction of the mass loss with the molecular clump.

9. We found SO/H₂S SO₂/H₂S 1, SO/SO₂ 1, OCS/H₂S 1 and SO/SiO 1. These column density ratios, applied at the time dependent model of Charnley (1997), indicate that the CB3 outflow in an evolved evolutionary stage, in agreement with the age estimations based on its dynamics.

© European Southern Observatory (ESO) 1999

Online publication: October 4, 1999
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