NED Abstract 
Copyright by American Astronomical Society.
Reproduced by permission

2002ApJ...565..959L

 Determination of the Distance to M33 Based on Single-Epoch I-Band Hubble
                Space Telescope Observations of Cepheids

                     Myung Gyoon Lee and Minsun Kim
 Astronomy Program, SEES, Seoul National University, Seoul 151-742, Korea;
             mglee@astrog.snu.ac.kr, mskim@astro.snu.ac.kr

                            Ata Sarajedini
     Department of Astronomy, University of Florida, P.O. Box 112055,
                Gainesville, FL 32611; ata@astro.ufl.edu

                                 and
                    Doug Geisler and Wolfgang Gieren
  Departamento de Fisica, Grupo de Astronomia, Universidad de Concepcion,
        Casilla 160-C, Concepcion, Chile; doug@kukita.cfm.udec.cl,
                        wgieren@coma.cfm.udec.cl
             Received 2001 July 2; accepted 2001 October 4

                              ABSTRACT
   We have determined the distance to M33 using single-epoch I-band
observations of Cepheids based on Hubble Space Telescope (HST)/Wide Field
Planetary Camera 2 (WFPC2) images of five fields in M33. Combining the 
HST I-band photometry and the periods determined from the ground-based
observations (DIRECT) for 21 Cepheids with log P > 0.8 in the sample of 32
Cepheids, we derive a distance modulus of (m - M)_0_ = 
24.52 +/- 0.14(random)+/-0.13(systematic) for an adopted total reddening of 
M33, E(B - V) = 0.20 +/- 0.04 [E(V - I) = 0.27 +/- 0.05] given by Freedman 
et al.; the reddening to the LMC, E(B - V) = 0.10; and the distance to the 
LMC, (m - M)_0_ = 18.50. If the total reddening to M33 of E(B - V) = 
0.10 +/- 0.09 given by Freedman, Wilson, and Madore is used, the Cepheid 
distance modulus based on the I-band photometry will be increased by 0.20. 
Metallicity effect on the Cepheid distance to M33 is estimated to be small, 
{delta}(m - M)_Z_ = 0.01-0.06, which leads to (m - M)_0_ = 24.53-24.58 
after this metallicity effect correction. Using the Wesenheit W_I_, an 
extinction-free parameter, we derive a similar value, (m - M)_0_ = 
24.52 +/- 0.15(random)+/-0.11(systematic). These results are in reasonable 
agreement with those based on the ground-based multiepoch BVRI observations 
of brighter Cepheids in M33 and are ~0.3 smaller than those based on the 
tip of the red giant branch and the red clump. It is needed to estimate 
better the reddening to Cepheids in M33.

Subject headings: Cepheids - galaxies: distances and redshifts - galaxies: 
individual (M33, NGC 598)