INFRARED OBSERVATIONS OF POSSIBLE HOT POSTASYMPTOTIC GIANT BRANCH STARS

Infrared photometry of seventeen high latitude early-type stars, that have either been identified as post-AGB objects or are post-AGB candidates, has been obtained at JHKL and nbM wavelengths. This has been combined with optical and IRAS observations, and compared with LTE model atmosphere fluxes; infrared excesses are found for five stars. Of the known post-AGB stars, only the highest mass objects reveal an infrared excess, suggesting a correlation between the presence of circumstellar material and mass. This may be explained in terms of the very different transition times for high and low mass post-AGB stars from the AGB to becoming a planetary nebula.