5. Conclusions

 

We have presented near infrared observations at J, H and K broad bands of the regions surrounding 31 SFR galactic H₂O and OH masers. The main conclusions, taking into account also the results of Paper I, are as follows:

1. we identified a K-band source within from the H₂O\ maser components in 73% of the cases (91% within ) and in 88% in the case of OH masers (95% within );
2. the NIR sources close to the masers and which are believed to be physically associated with them, have colours which differs from those of the field stars, showing in most cases a remarkable near infrared excess at 2.2 m;
3. the separation between the maser components and the associated NIR sources is in most cases less than 10⁴ AU;
4. the NIR sources associated with the maser components appear to be young massive stars in their earliest evolutionary stages.

One of the major results of this work is that even in fields overcrowded by foreground/background stars it is possible to find the NIR source physically associated with the masers by examining the positional coincidence and the NIR colours. We argue that this is the general situation, namely that the masers are always associated with a NIR source with strong infrared excess and that this is the ultimate energy source for the maser action.

Acknowledgements

We thank R. Forster for providing unpublished VLA data. Support from C.N.R.-N.A.T.O. Advanced Fellowship program and from NASA's Origins of Solar Systems program (through grant NAGW-4030) is gratefully aknowledged.