Imaging the circumstellar envelope of OH 26.5+0.6

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

Corresponding author: K. Justtanont, kay@astro.su.se

Received: 10 July 2002
Accepted: 28 August 2002

Abstract

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 –0 line transition. The CO emission is partially resolved with a deconvolved source size of . 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  yr^-1. From this we are able to place an upper limit on the extent of the dusty envelope of 10¹⁶ cm while our BIMA map shows that the CO photodissociation radius extends out to about  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.