A search for symbiotic behaviour amongst OH/IR colour mimics

Recent maser surveys have shown that many potential OH/IR stars have no OHmasers in their circumstellar envelopes, despite the modest requirements whichshould be implicitly met by IRAS colour-selected candidates. It has beensuggested that these OH/IR colour mimics must have a degenerate companion whichdissociates OH molecules and disrupts the masing action, ie. that they arerelated to symbiotic Miras. Coincidentally, there is a paucity of long-periodsymbiotic Miras and symbiotic OH/IR stars. Phenomonologically, those that areknown seem to cluster in the zone where field Miras transform into OH/IR stars.If it could be proven that OH/IR colour mimics contain a degenerate star, thatobservable evidence of this star is hidden from view by CS dust whilst itslowly accretes from the wind of its Mira companion, then we have an excellentexplanation for not only the existence of OH/IR colour mimics, but also for thelow observed frequency of symbiotic OH/IR stars and the common occurrence ofvery slow novae in long-period symbiotic Miras. Here, we employ radio continuumradiation (which should escape unhindered from within the dust shells) as asimple probe of the postulated hot degenerate companions which would inevitablyionize a region of their surrounding gas. We compare the radio and infraredproperties of the colour mimics with those of normal symbiotic Miras, using thestrong correlation between radio and mid-IR emission in symbiotic stars. Weshow that if a hot companion exists then, unlike their symbiotic counterparts,they must produce radiation-bounded nebulae. Our observations provide nosupport for the above scenario for the lack of observed masers, but neither dothey permit a rejection of this scenario.Comment: 6 pages; no figures attached; LaTeX (MN style); postscript figures via anonymous ftp in users/ers/mimic-figs on astro.caltech.edu; University of Toronto pre-print; ERSRJI