Determination of the Distance to M33 Based on the Tip of the Red Giant Branch and the Red C.pdf

a r X i v : a s t r o - p h / 0 1 1 0 0 0 6 v 1 2 9 S e p 2 0 0 1 Draft version February 1, 2008 Preprint typeset using LATEX style emulateapj v. 21/08/00 DETERMINATION OF THE DISTANCE TO M33 BASED ON THE TIP OF THE RED GIANT BRANCH AND THE RED CLUMP1 Minsun Kim, Eunhyeuk Kim, Myung Gyoon Lee Astronomy Program, SEES, Seoul National University, Seoul, 151-742, Korea Ata Sarajedini Department of Astronomy, University of Florida, P.O.Box 112055, Gainsville, FL 32611, USA Doug Geisler Departamento de F??sica, Grupo de Astronom??a, Universidad de Concepcio?n, Casilla 160-C, Concepcio?n, Chile Draft version February 1, 2008 ABSTRACT We have determined the distance to M33 using the tip of the red giant branch (TRGB) and the red clump (RC), from the V I photometry of stars in ten regions of M33 based onHST/WFPC2 images. The regions used in this study are located at R = 2.6 ? 17.8 arcmin 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. Subject headings: galaxies: distances and redshifts — galaxies: individual (M33 (NGC 598)) — stars: tip of the red giant branch (TRGB) — stars: red clump(RC) 1. introduction The accurate determination of the distances to Local Group galaxies is critical in the study of the extragalac- tic distance scale. In particular two spiral galaxies in the Local Group, M31 and M33, are primary calibrators for several secondary distance indicators inclu