Distance and Reddening of the Isolated Dwarf Irregular Galaxy NGC 1156
  We present a photometric estimation of the distance and reddening values to
the dwarf irregular galaxy NGC 1156, which is one of the best targets to study
the isolated dwarf galaxies in the nearby universe. We have used the imaging
data sets of the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS)
High Resolution Channel (HRC) of the central region of NGC 1156 (26" X 29")
available in the HST archive for this study. From the (U-B, B-V) color-color
diagram, we first estimate the total (foreground + internal) reddening toward
NGC 1156 of E(B-V) =0.35 +/- 0.05 mag, whereas only the foreground reddening
was previously known to be E(B-V)=0.16 mag (Burstein & Heiles) or 0.24 mag
(Schlegel, Finkbeiner, & Davis). Based on the brightest stars method, selecting
the three brightest blue supergiant (BSG) stars with mean B magnitude of
<B(3B)> = 21.94 mag and the three brightest red supergiant (RSG) stars with
mean V magnitude of <V(3R)> = 22.76 mag, we derive the distance modulus to NGC
1156 to be (m-M)_{0,BSG} = 29.55 mag and (m-M)_{0,RSG} = 29.16 mag. By using
weights of 1 and 1.5 for the distance moduli from using the BSGs and the RSGs,
respectively, we finally obtain the weighted mean distance modulus to NGC 1156
(m-M)_0 = 29.39 +/- 0.20 mag (d = 7.6 +/- 0.7 Mpc), which is in very good
agreement with the previous estimates. Combining the photometry data of this
study with those of Karachentsev et al. gives smaller distance to NGC 1156,
which is discussed together with the limits of the data.
