  We present contemporaneous HST WFPC2 and VLA observations of the symbiotic
nova HM Sge. We identify a number of discreet features at spatial scales
smaller than approximately 0.1 arcsec embedded in the extended nebula, with
radio and optical emission well correlated in the inner 1 arcsec. For the first
time we measure the positions of the binary components of a symbiotic star
directly. We estimate the projected angular binary separation to be 40+/-9
milli-arcsec, with the binary axis at position angle 130+/-10 degrees. The
latter is consistent with previous estimates made by indirect methods. The
binary separation is consistent with a previous estimate of 50 au if the
distance is 1250+/-280 pc. Temperature and density diagnostics show two
distinct regions in the surrounding nebula, with a cool wedge to the
south-west. An extinction map indicates the true interstellar extinction to be
no more than E(B-V) = 0.35. This is consistent with a minimum distance of
approximatelly 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 suggest that a southern concentration
of dust and the south-west wedge are associated with the cool component wind.
Alternatively, the southern dust concentration is the cause of the cool wedge,
as it shields part of the nebula from the hot component radiation field.
