SIMBAD references

We present observations of the polarized water maser-flare source in Orion during the last years of its life, when we found low intensity but very high polarization. We also propose a geometrical model in which the maser source is formed in the central part of an edge-on protoplanetary ring. This model explains the linear variation of the maser velocity with position, detected in VLBI observations, as the projection of the Keplerian orbital velocity in the direction of the line of sight. It also explains the high brightness temperatures as the amplification of the radiation emitted by the back part of the ring by the front of it. Variability will be due to inhomogeneities in the ring, strong emission will occur when dense clumps of material are aligned in the observer's direction, the life-time of this strong emission will depend on the size of the clumps and on their relative velocities. Polarization properties are possibly due to both geometry and magnetic fields. From the observed velocity gradient and from saturation considerations we derive a lower limit of 15M_☉ for the central star, a diameter for the ring of 80AU and a width of 1.6AU.