Variable Stars in Local Group Galaxies. I. M33

A search for variable stars in M33 has been made using a series of red plates taken over a 4 yr interval from 1982 through 1985. Limiting plate magnitudes correspond to r = 21.7 mag. The total sample of variables for which periods have been determined consists of 54 long-period variables, 90 Cepheids (69 new periods), and six probable W Virginis variables. An additional 244 variables have been identified, but no regular periods have been determined. At least one of these is a Hubble-Sandage variable, but most are probably Cepheids and long-period variables. Infrared JHK photometry of a small sample of the red supergiant variables, when compared to the period-luminosity law for red supergiant variables in the Large Magellanic Cloud, yields an apparent distance modulus to M33 in K of 24.64±0.10.