The Distance of the Local-Group Galaxy IC 1613 Obtained from Baade's Work on its Stellar Content

Fifty-nine variables were found by Baade over the face of IC 1613 from a series of plates taken with the 100-inch reflector from 1929 to 1937. Of these, thirty-seven are definite Cepheids ranging in period from 146 days to 2 days, four are probable Cepheids, thirteen are irregular, one is a probable SRc, one is an eclipsing binary, and three are of unknown type. Photometry depends on a photoelectric sequence of thirty-eight stars measured with the 200-inch reflector in the interval 11.6 < B < 21.7. Magmtndes of 279 secondary standards used for the variables have been determined relative to the basic sequence. The values are listed in the Appendix. Two interpretations of the period-luminosity relation are given for the Cepheids. The apparent blue modulus is (rn - M)AB = 24.55 as found from the most recent calibration of the P-L relation. A reddening of E(B - V) 0.03 gives the true modulus as (m - Al)0 = 24.43. The integrated absolute magnitude of IC 1613 is MB = -14.45. The brightest blue supergiant is star 22A with ` B = -7.55. The brightest red supergiant is the irregular red variable V42 with MB = -6.05, or Mv -8.0 if B = V is assumed to be 2.0. The largest Hii region has a linear size of 167 pc. These absolute magnitudes and linear dimensions are much smaller than corresponding values in intrinsically brighter late-type galaxies. The total extent of the Population II component of IC 1613 is by 20;3, or 5600 by 4500 pc. The Population I component covers a region only half these dimensions.