The mass loss history of high latitude supergiants

A sample of 25 high latitude supergiants with spectral types B-G were surveyed in the (C-12)O J = 1-0 and J = 2-1 lines using the Swedish ESO Submillimeter Telescope (SEST). Twenty percent of the sources were detected. For the analysis an additional six sources were added for which CO observations are reported in the literature. The majority of the detected sources have post-AGB mass loss rates and expansion velocities that confirm earlier suggestions that these stars, despite their supergiant-like spectra, are in fact low mass post-AGB stars (Trams et al. 1989). The nondetections and their systematic lower 60 micron fluxes can be explained assuming that they are low mass post-AGB stars, whose remnant AGB shells are significantly diluted and which are evolving rather slowly to higher temperatures.