Observational investigation of mass loss of M supergiants

We present the analysis of infrared photometry and millimeter spectroscopy of a sample of 74 late-type supergiants. These observations are particularl y suitable to study the mass loss and the circumstellar envelopes of evolve d massive stars. In particular, we quantify the circumstellar infrared exce ss, the relation of mass loss with stellar properties, using the K-[12] col our index as mass-loss indicator. We do not find any clear correlation betw een mass loss rate and luminosity. We also show that the K-band magnitude i s a simple luminosity indicator, because of the relative constancy of the K -band bolometric correction.