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Astron. Astrophys. 360, L9-L12 (2000)

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1. Introduction

Frosty Leo (IRAS 09371+1212) is a well-known bipolar nebula around a star believed to be in the short transition phase between the AGB and planetary nebula evolutionary phases - i.e. it is a protoplanetary nebula (PPN). Forveille et al. (1987)first identified it as an evolved object with substantial CO line emission showing the presence of a dense expanding molecular envelope, and suggested the presence of water ice in its dust grains, confirmed later by e.g. Rouan et al. (1988). Optical and near-IR imaging of Frosty Leo revealed a remarkable extended point-symmetric bipolar reflection nebula with a pair of peripheral ansae and bisected by a dense disk seen edge-on (Morris & Reipurth 1990 , Langill et al. 1994). Roddier et al. (1995) found a binary star at the center of the nebula from adaptive optics imaging at 1.65 µm. We report here optical imaging with the Hubble Space Telescope (HST) of Frosty Leo, revealing complex new nebular structures which have important implications for the shaping of planetary nebulae (PNe). New, sensitive millimeter-wave observations indicate a complex kinematic structure of the molecular gas. In our analysis of these data, we assume that the central star has [FORMULA]=3750K, luminosity L=250(D/kpc)2[FORMULA], and is located at a distance D=3 kpc (Robinson et al. 1992 , Mauron et al. 1989).

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© European Southern Observatory (ESO) 2000

Online publication: August 17, 2000