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 \hbox { $ { } ^ { \prime \prime } $ } \times 29 \hbox { $ { } ^ { \prime \prime } $ } ) 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 \pm 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 \langle B ( 3 B ) \rangle = 21.94 mag and the three brightest red supergiant ( RSG ) stars with mean V magnitude of \langle V ( 3 R ) \rangle = 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 \pm 0.20 mag ( d = 7.6 \pm 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 .