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Astron. Astrophys. 334, L5-L8 (1998)

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Letter to the Editor

Variable sub-arcsecond structure
in the circumstellar envelope of IRC+10216 *

C.A. Haniff 1 and D.F. Buscher 2

1 Mullard Radio Astronomy Observatory, Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE, UK
(cah@mrao.cam.ac.uk)
2 Department of Physics, University of Durham, South Road, Durham DH1 3LE, UK (david.buscher@durham.ac.uk)

Received 6 March 1998 / Accepted 7 April 1998

Abstract

We present new diffraction-limited interferometric images of the carbon star IRC+10216 at wavelengths of 2.2µm and 3.4µm. These show that the distribution of the near-infrared emission from the star departs significantly from a spherical geometry on 0.1 arcsecond scales. At 3.4µm, i.e. close to the peak of the star/dust-shell spectral energy distribution, approximately 60% of the flux comes from regions asymmetrically disposed about the stellar photosphere at radii of 0.1-0.3 arcseconds. Images taken in 1989 and 1997 show large changes in the distribution of flux, but a consistent axis of symmetry at a PA of approximately [FORMULA]. Archival Hubble Space Telescope images at 0.79 and [FORMULA] m show filaments with the same symmetry axis and a dark lane perpendicular to this axis approximately 0.25 arcseconds to the north of the star. Taken together, these data suggest a model in which the asymmetries seen are a consequence of envelope clearing along a bipolar axis. These observations indicate that the asymmetries seen in planetary nebulae may already be established before the progenitor star has left the AGB.

Key words: stars, AGB – stars, individual: IRC+10216 – stars, mass-loss

* Based, in part, on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under the NASA contract NAS 5-26555.

Send offprint requests to: C.A. Haniff

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© European Southern Observatory (ESO) 1998

Online publication: May 12, 1998

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