  Red supergiants (RSGs) are an evolved stage in the life of intermediate
massive stars (than than 25 solar masses). For many years, their location in
the H-R diagram was at variance with the evolutionary models. Using the MARCS
stellar atmospheres, we have determined new effective temperatures and
bolometric luminosities for RSGs in the Milky Way, LMC, and SMC, and our work
has resulted in much better agreement with the evolutionary models. We have
also found evidence of significant visual extinction due to circumstellar dust.
Although in the Milky Way the RSGs contribute only a small fraction (than than
1 percent) of the dust to the interstellar medium (ISM), in starburst galaxies
or galaxies at large look-back times, we expect that RSGs may be the main dust
source. We are in the process of extending this work now to RSGs of higher and
lower metallicities using the galaxies M31 and WLM.
