| Abstract | We have determined the distance to M33 using the tip of the red giant branch (TRGB) and the red clump (RC), from the VI photometry of stars in 10 regions of M33 based on HST/WFPC2 images. The regions used in this study are located at R=2.6′-17.8′ from the center of M33. The distance modulus to M33 obtained in this study, for an adopted foreground reddening of E(B-V)=0.04, is (m-M)0,TRGB=24.81+/-0.04(random)+0.15- 0.11(systematic) from the TRGB, and (m-M)0,RC=24.80+/-0.04(random)+/-0.05(systematic) from the RC, showing an excellent agreement between the two [corresponding to a distance of 916+/-17(random) kpc and 912+/-17(random) kpc, respectively]. These results are ~0.3 mag larger than the Cepheid distances based on the same HST/WFPC2 data and ground-based data. This difference is considered partially due to the uncertainty in the estimates of the total reddening for Cepheids in M33. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. |
