TESTING THE BINARY HYPOTHESIS FOR OH/IR COLOUR MIMICS

maser surveys have shown that many potential oh/ir stars have no oh masers in their cs envelopes, despite modest requirements which should be implicitly met by iras colourselected candidates. it is probable that these oh/ir colour mimics. are related to symbiotic stars and have a degenerate companion (hidden in the optical and nearir by circumstellar dust) which disrupts the masing action. here we propose to compare farir line emission from colour mimics with that from symbiotic stars. the circumstellar dust shells will be much less opaque in the farir and, since a hot companion would inevitably stimulate line emission, our spectra will constitute a simple and effective test of whether hot stars are present. line intensities and ratios for symbiotics (and mimics, if lines are detected) will be used to analyse abundances and ionization conditions. the temperature of any colour mimic companions will help to tie down the mechanism (be it radiative or gravitational) by which masers are suppressed in symbiotic miras. our sample contains examples of colour mimics with a range of iras colours and lrs types, as well as symbiotics with agb giants and firstascent giants. these have been chosen to avoid duplication of the symbiotic and oh/ir stars in the core programme. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]