EDP Sciences
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Volume 396, Number 2, December III 2002
Page(s) 581 - 587
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20021272

A&A 396, 581-587 (2002)
DOI: 10.1051/0004-6361:20021272

Imaging the circumstellar envelope of OH 26.5+0.6

D. Fong1, K. Justtanont2, M. Meixner1 and M. T. Campbell1

1  Department of Astronomy, University of Illinois, 1002 W. Green Street Urbana, IL 61801, USA
2  SCFAB, Stockholm Observatory, Department of Astronomy, 106 91 Stockholm, Sweden

(Received 10 July 2002 / Accepted 28 August 2002)

Using the Berkeley-Illinois-Maryland-Association (BIMA) Millimeter Array, we were able to map the extreme OH/IR star, OH 26.5+0.6, in the 12CO J=1-0 line transition. The CO emission is partially resolved with a deconvolved source size of $8.5\arcsec \times 5.5\arcsec$. The spectrum shows that the blue-shifted emission is missing, most likely due to interstellar absorption. By modelling the infrared spectral energy distribution, we derive a dust mass loss rate of $1.9\times10^{-6}~ M_{\odot}$ yr -1. From this we are able to place an upper limit on the extent of the dusty envelope of 10 16 cm while our BIMA map shows that the CO photodissociation radius extends out to about $7\times10^{16}$ cm. To best fit the BIMA observations and the higher CO rotational transitions using our full radiative transfer code, we needed to include a second, more tenuous AGB wind, outside the high density superwind to account for the observed flux. From our model, we conclude that up to 80% of the CO flux comes from the unresolved superwind.

Key words: stars: AGB and post-AGB -- stars: circumstellar matter -- stars: individual : OH 26.5+0.6 -- stars: late-type -- stars: mass loss

Offprint request: K. Justtanont, kay@astro.su.se

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