Studies of Extreme Carbon Stars

Rocket and satellite IR sky surveys have revealed vast populations of extreme AGB stars with substantial circumstellar dust shells. It is normally assumed that these shells permit essentially no light to escape. However, using the Lick 3 meter reflector we have been able to secure and analyze a large number of spectra of a well-defined sample of these extreme evolved stars. From this archive we have determined that these objects are all long period Mira variables and have estimated their periods, correlated these with IR photometric variations, and deduced distances to the stars. The data reveal a population of disk carbon-giants, typically of 1-2 yr periods, mostly within 2 kpc of the sun. We have also been able to quantify the thickness of their dust shells.