NEBULAR EMISSION-LINES IN IRAS 10215-5916

From low and high resolution spectroscopic observations of IRAS 10215 - 5916 we have discovered the presence of nebular emission lines in th is G-type supergiant star in the post-AGB stage. From its high resolut ion spectrum we derived an expansion velocity of 17 km s-1 for the she ll, similar to the values usually observed in planetary and proto-plan etary nebulae. The images taken in the near infrared show that IRAS 10 215-5916 is slightly extended and asymmetric. Although we cannot rule out a possible binary nature for the central star of this IRAS source, in which a hot component could be the responsible for the observed ne bular emission, no indications of binarity have been found so far. We suggest that the observed spectrum and morphology could be produced by the asymmetric mass loss of a single star in the post-AGB phase. Post -AGB mass loss can play a fundamental role on shortening the transitio n time towards the planetary nebula stage and favour the formation of the bipolar structures commonly observed in evolved planetary nebulae. In this sense, it is shown that this mass loss is more intense and fr equent for massive progenitors of PNe.