  SRC variables are M supergiants, precursors to Type II supernovae, that vary
in brightness with moderately regular periods of order 100-1000 days. Although
identified as pulsating stars that obey their own period-luminosity relation,
few have been examined in enough detail to follow the temperature and spectral
changes that they undergo during their long cycles. The present study examines
such changes for several SRC variables revealed by CCD spectra obtained at the
Dominion Astrophysical Observatory (DAO) during 2005-2009, as well as by
archival spectra from the DAO (and elsewhere) for some stars from the 1960s to
1980s, and Cambridge radial velocity spectrometer measures for Betelgeuse.
Described here is our classification procedure and information on the spectral
type and radial velocity changes in three of the stars. The results provide
insights into the pulsation mechanism in M supergiants.
