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J.M. Torrelles (IEEC/CSIC), N.A. Patel (CfA), J. Gómez (LAEFF), P.T.P. Ho (CfA), L.F. Rodr\'{i}guez (UNAM), G. Anglada (CfA), G. Garay (UC), L. Greenhill (CfA), S. Curiel, J. Cantó (UNAM)
We report three epochs of VLBA water vapour maser observations toward the star forming region Cepheus A. The VLBA data show that some of the masers detected previously with the VLA unfold into unexpected and remarkable linear/arcuate continuous ``microstructures''. Both the morphology and the observed proper motions found in these water maser structures have allowed us to identify at least three different centers of star formation activity, unknown previously, in a region of 300 mas (200 AU) projected radius and that could constitute a triple star system. The flattened appearance of the small ``building-blocks'' constituting these water maser structures argues strongly for a shock nature. One of the water maser microstructures defines an expanding circle of ~q 62 AU radius at the precision of one part in a thousand. We have interpreted this structure as due to a spherical ejection of material 33 years earlier from a protostar. The physical processes involved to produce such highly spherically symmetric ejection are not known, introducing new constraints for theories on how stars evolve in their early stages.