MERLIN OBSERVATIONS OF BIPOLAR OUTFLOW FROM HM SAGITTAE

MERLIN maps of HM Sagittae at 6-cm and 18-cm wavelengths are presented . At 6 cm, the inner nebula has been mapped at a resolution of 60 mill i-arcsec (mas), revealing two parallel ridge structures to the north a nd south of a deep central minimum. In addition, these central feature s are surrounded by a complex, weak structure. The ridges and many of the weak features are correlated with ultraviolet (UV) structure obser ved with the Hubble Space Telescope (HST). The 18-cm map reveals elong ated structure to the east and west of the star's position. There is s trong evidence that the eastern and western edges of this extension ar e non-thermal. The E-W and N-S features are associated with components detected with optical spectroscopy. The radial velocities of these co mponents suggest that the E-W features are a high-velocity bipolar out flow. We argue that the brightness temperature of similar to 45 000 K for the N-S features results from shock heating by the outflow. The re sulting expansion velocity, when compared with the observed proper mot ion, implies a distance of 3.2 kpc.