HM Sagittae - A most remarkable star.

HM Sagittae is one of the most unusual objects in the Galaxy for it displays activity in every spectral band from X-ray to radio. HM Sge is probably best described by a binary system consisting of a late M giant and a hot compact object which is similar to central stars of planetary nebulae. The presence of a wind from the M giant implies that Roche-lobe overflow is not a necessary condition for mass transfer. The complex structure of the circumstellar nebula is possibly the result of wind interactions. The ongoing spectral evolution of HM Sge after its recent outburst makes it an ideal candidate to test models of the symbiotic phenomena.