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Astron. Astrophys. 320, 575-579 (1997)

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CS chemistry in the bipolar nebula CRL 2688

T. Kasuga 1, 2, I. Yamamura 3, 4, 5 and S. Deguchi 2

1 Department of Instrument and Control Engineering, Hosei University, Kajino 3-7-2, Koganei, Tokyo 184, Japan
2 Nobeyama Radio Observatory, National Astronomical Observatory, Minamimaki, Minamisaku, Nagano 384-13, Japan
3 Department of Astronomy, School of Science, University of Tokyo, Bunkyo, Tokyo 113, Japan
4 Institute of Astronomy, Faculty of Science, University of Tokyo, Osawa 2-21-1 Mitaka, Tokyo 181, Japan
5 temporary address: SRON Laboratory for Space Research Groningen, P. O. Box 800, 9700 AV Groningen, The Netherlands

Received 21 May 1996 / Accepted 17 September 1996

Abstract

High spatial-resolution observations of the protoplanetary nebula CRL2688 were made by the CS [FORMULA] 1-0 and [FORMULA] 2-1 lines with the Nobeyama Millimeter Array with angular resolutions of [FORMULA] and [FORMULA], respectively. The mapping observations reveal that strong CS peaks in the [FORMULA] 2-1 line are located symmetrically at both sides of the optical dark lane at the center, though the CS [FORMULA] 1-0 distribution is rather round. These CS peaks seem to be slightly misaligned from the optical bipolar axis. A modeling of the CRL 2688 envelope results that the density distribution is nearly spherically symmetric but the abundance of CS is enhanced near the polar regions. The increase of the CS abundance near the poles can be explained by the chemistry of sulfur containing molecules in the postshocked region in the high-velocity flow.

Key words: stars: CRL 2688 – stars: AGB, post-AGB – stars: mass loss – circumstellar matter – radio lines: stars

Send offprint requests to: S. Deguchi2 ; deguchi@nro.nao.ac.jp

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998
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