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 = 21.94 mag and the three brightest red supergiant (RSG) stars with mean V magnitude of = 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.Comment: 18 pages, 8 figures, Accepted by PASJ (2012 Apr issue

Impacts of Detailed Land-Use Types and Urban Heat in an Urban Canopy Model on Local Meteorology and Ozone Levels for Air Quality Modeling in a Coastal City, Korea

An urban canopy model (UCM), with detailed urban land-use and anthropogenic heat information, is required to reproduce and understand the urbanization process and its impact on regional climate and urban air quality. This study investigates the UCM impact on simulated meteorology and surface ozone in the coastal city of Busan using the WRF-SMOKE-CMAQ model coupled with (UCM case), and without the UCM (NOUCM case). The UCM and NOUCM case results suggest that UCM case generally produces warmer temperatures and deeper planetary boundary layer (PBL) heights, especially in the early morning and night time, than the NOUCM case. Owing to urban heating and enhanced turbulent mixing incorporation in the center of the city, the sea breeze in the UCM case tends to penetrate faster and more strongly than in the NOUCM case. After sea breeze arrival at the urban center, the urban heat island effect prevents its penetration further inland. In the UCM case in the late afternoon, local meteorological changes induce remarkable increases in simulated O3 concentrations over the downwind (up to 17.1 ppb) and downtown (up to 10.6 ppb) areas. This is probably due to an increase in temperature in the urban areas and the wind convergence zone movement due to the sea breeze interaction and offshore flows. The increase in O3 concentration in the late afternoon results in the model bias reduction under previously underestimated O3 conditions due to high NOx emissions. The simulated O3 concentrations in the UCM case are more similar to the observed O3 concentrations compared to those of the NOUCM case