We present the first spectropolarimetric observations of the symbiotic nova
HM Sge. We first note that marked spectral changes occurred: in the near I
R the spectrum of the Mira in the system has clearly appeared. The nebular
emission line spectrum remains largely unchanged but we detect for the firs
t time the Raman line at lambda 6825. These changes indicate that the dust
content in HM Sge is rapidly decreasing and chat the dust obscuration perio
d which began in 1985 has come to an end.
In terms of polarization we find that the red giant spectrum is intrinsical
ly polarized at the 0.5 % level and the polarization signal is structured a
cross the TiO absorption bands. The Raman scattered O VI line at lambda 682
5 shows a polarization of 3.4 % at an angle of 33 degrees. The behaviour of
the polarization angle across the Raman line strongly indicates that an ax
isymmetric O VI-H I scattering geometry prevails. The distribution of the n
eutral hydrogen in the inner binary system does not seem to be strongly per
turbed by binary motion. We conclude that the present binary axis is orient
ated at a position angle of similar to 123 degrees.
The deduced orientation of the binary axis of HM Sge is parallel or perpend
icular to distinct geometric features of the surrounding nebulosity. This i
ndicates that the orientation of the binary system is of prime importance f
or the understanding of the nebular structure.