Our observations have shown that the circumstellar H2O maser can amplify the stellar image and produce a strong stellar image, a phenomenon previously detected at the OH maser transitions. Although this effect is not necessarily strong in all H2O masers, it can be very valuable for astrometric purposes. Accurate astrometry of the stellar image can be used to determine the location of the various maser species in the CSE with respect to each other and the star. Simultaneous, high resolution observations significantly improve our understanding of the kinematics in the CSEs. Using the stellar image in H2O masers, it will also be possible to determine the stellar trajectory and distance with a higher accuracy than with OH masers. However, because of the high variability of H2O masers additional monitoring will have to be performed to show if the stellar image is persistent enough for a long term monitoring campaign.
Acknowledgements
This project is supported by NWO grant 614-21-007. MERLIN is a National Facility operated by the University of Manchester at Jodrell Bank Observatory on behalf of PPARC. We also thank the referee Mark Reid for valuable input.
Copyright ESO 2002