Astron. Astrophys. 325, 725-744 (1997)

7. Conclusions

We have taken single dish and interferometer maps (at millimeter wavelengths) and NIR images (in the J, H, and K bands) of the molecular cloud surrounding the IRAS point source IRAS 20126+4104 and the associated H₂ O masers. This region was selected from a sample of H₂ O maser sources with IRAS counterpart but no associated continuum emission, with the aim of identifying massive (proto)stars in a phase prior to the formation of an HII region.

Many different molecular species have been observed with angular resolution from to and a few (in particular HCO (1-0) and CH₃ CN(5-4)) with higher angular resolution (). The main results are the followings:

1. IRAS 20126+4104 is embedded in a molecular clump seen in all tracers, which is centred on the H₂ O masers position and is  pc large; its temperature and mass are  K and .
2. A bipolar outflow seen in the HCO (1-0) and CS(3-2) lines arises from the centre of the clump and extends on a scale of  pc along the SE-NW direction. The mass loss rate, momentum, and mechanical luminosity of such outflow are large suggesting it to arise from a young active stellar object in an early and active stage of its formation.
3. The H₂ O masers, NIR continuum, and H₂ line emission look elongated in the same direction as the bipolar structure seen in HCO at high angular resolution, thus confirming the interpretation of this as a bipolar outflow ejected from a central source coincident with the nominal position of IRAS 20126+4104.
4. The high density tracers like CH₃ CN map a dense compact core of diameter  pc centred on the H₂ O masers, with temperature  K and mass . Although only barely resolved, we find evidence for such core being elongated in a direction perpendicular to the outflow axis and subject to a velocity field which we interpret as rotation around that axis.
5. The luminosity of the core, the IRAS colours of IRAS 20126+4104, the presence of H₂ O masers and the existence of a faint 3.6 cm continuum emission (Marti & Rodriguez in prep) coincident with the 3.3 mm continuum peak indicate that such core contains a very young B2.5-B0.5 (proto)star.

We conclude that IRAS 20126+4104 represents a rare beautiful example of a disk-outflow system originating from a young early type massive (proto)star still in an evolutionary phase prior to the development of an UC H II region.

© European Southern Observatory (ESO) 1997

Online publication: April 28, 1998

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