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Astron. Astrophys. 353, L5-L8 (2000)

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1. Introduction

Neutral envelopes are widely detected around planetary nebulae (PNe) and provide important links with the precursor AGB and proto-PN phases (Huggins et al. 1996). The neutral gas plays a critical role in the morphology of the ionized nebulae, so the evolution of the envelopes is an important factor in PN shaping. One mechanism that shapes the neutral gas is interaction with collimated outflows or jets. Recent optical studies have shown that these are common, especially in young PNe (e.g., López 1997, Sahai & Trauger 1998), and observations of molecular gas in a number of cases directly reveal their shaping effects on the envelopes (e.g., Forveille et al. 1998; Cox et al. 1999a).

BD+30o3639 (PN 064+05.0) is one of the most intensively studied PNe. It has been observed from x-ray to radio wavelengths, including optical imaging with the HST (Harrington et al. 1997). The low temperature of the central star ([FORMULA] K) and the short expansion time of the nebula (900 yr, Kawamura & Masson 1996) confirm its recent emergence from the proto-PN phase. The ionized nebula shows a classic ring morphology, and it is one of the rare cases where x-rays have actually been detected and may signal the presence of a wind-shocked bubble inside the nebula, as expected in the interacting-winds model (Arnaud et al. 1996).

Surrounding BD+30o3639 is a massive envelope of neutral gas which has been observed in several species, including H I (Taylor et al. 1990), H2 (Cox et al. 1999b, Shupe et al. 1998, and references therein), and CO (Bachiller et al. 1991, 1992). The dominant mass of the envelope is in H I , but it is not currently possible to map this in any detail. Images of the envelope in H2 reveal a disturbed, expanding, molecular torus, and a most unusual feature is seen in CO. The CO spectrum shows gas only at high expansion velocities of [FORMULA] km s-1, roughly twice that of the bulk of the ionized nebula and the H I envelope. In order to investigate this we have observed the CO at high angular resolution, and we report the results in this letter. We find that the CO emitting gas forms a highly-collimated, bipolar structure which cannot be explained by the interacting-winds model, and demonstrates the importance of outflows or jets in shaping the nebula.

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© European Southern Observatory (ESO) 2000

Online publication: December 17, 1999
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