The inner nebula and central binary of the symbiotic star HM Sagittae

We present contemporaneous Hubble Space Telescope Wide Field Planetary Came ra 2 and Very Large Array observations of the symbiotic nova HM Sge. We ide ntify a number of discreet features at spatial scales smaller than embedded in the extended nebula, with radio and optical emission well correlated in the inner 1 ". For the first time we measure the positions of the binary c omponents of a symbiotic star directly. We estimate the projected angular b inary separation to be 40 +/- 9 mas, with the binary axis at a position ang le of 130 degrees +/- 10 degrees. The latter is consistent with previous es timates made by indirect methods. The binary separation is consistent with a previous estimate of 50 AU if the distance is 1250 +/- 280 pc. Temperatur e and density diagnostics show two distinct regions in the surrounding nebu la, with a cool wedge to the southwest. An extinction map indicates the tru e interstellar extinction to be no more than E(B-V) = 0.35. This is consist ent with a minimum distance of similar to 700 pc, but this would be reduced if there is a circumstellar contribution to the minimum in the extinction map. The extinction map also suggests a patchy dust distribution. We sugges t that a southern concentration of dust and the southwest wedge are associa ted with the cool component wind. Alternatively, the southern dust concentr ation is the cause of the cool wedge, since it shields part of the nebula f rom the hot-component radiation field.