| Abstract | New data on the distance to M33 obtained by photometry of some of its Cepheids are reported. Blue light curves and periods between 37 and 3 days for 13 Cepheids in a clear, far outlying region of M33 give a well-defined period-luminosity (P-L) relation whose slope and scatter are the same as the corrected data for Hubble's original Cepheids and for Cepheids in the Large Magellanic Cloud. The apparent blue distance modulus of M33 is 25.35, determined by applying an adopted P-L relation to the data. A consequence of this distance, which is about 0.7 mag larger than heretofore adopted, is to make the use of red supergiants as distance indicators more complicated than previously believed. The new M33 data, combined with newly discovered, brighter red stars in M101, suggest a dependence of the red supergiant luminosity on the luminosity of the parent galaxy, if the MB of the galaxy is brighter than about -19. |
