Abstract
We present measurements of reddening due to dust using the colors of stars in the Sloan Digital Sky Survey (SDSS). We measure the color of main sequence turn-off stars by finding the "blue tip" of the stellar locus: the prominent blue edge in the distribution of stellar colors. The method is sensitive to color changes of order 18, 12, 7, and 8 mmag of reddening in the colors u-g, g-r, r-i, and i-z, respectively, in regions measuring 90' by 14'. We present maps of the blue tip colors in each of these bands over the entire SDSS footprint, including the new dusty southern Galactic cap data provided by the SDSS-III. The results disfavor the best fit O'Donnell (1994) and Cardelli et al. (1989) reddening laws, but are well described by a Fitzpatrick (1999) reddening law with R_V = 3.1. The SFD dust map is found to trace the dust well, but overestimates reddening by factors of 1.4, 1.0, 1.2, and 1.4 in u-g, g-r, r-i, and i-z, largely due to the adopted reddening law. In select dusty regions of the sky, we find evidence for problems in the SFD temperature correction. A dust map normalization difference of 15% between the Galactic north and south sky may be due to these dust temperature errors.
Highlights
Most astronomical observations are affected by Galactic interstellar dust, whether as a source of foreground light in the microwave, far-infrared (FIR), and gamma-ray wavelength regions or as a cause of extinction in the infrared through ultraviolet (Draine 2003)
Dust is formed as stars burn nuclear fuel to form heavy elements and emit these elements in stellar winds or in more violent eruptions, and these elements are reprocessed in the interstellar medium (ISM; Draine 2009)
The BH dust map was superseded by the Schlegel et al (1998, hereafter SFD) dust map, which took advantage of the full-sky FIR data provided by IRAS and DIRBE, which are dominated by thermal emission from the Galactic dust at wavelengths of 100 μm and longer
Summary
Most astronomical observations are affected by Galactic interstellar dust, whether as a source of foreground light in the microwave, far-infrared (FIR), and gamma-ray wavelength regions or as a cause of extinction in the infrared through ultraviolet (Draine 2003). We perform tests similar to these in regions of lower extinction than had been previously possible, taking advantage of the high quality and depth of the SDSS stellar photometry, and complementing the recent work of Peek & Graves (2010), who use SDSS galaxy spectra. In these regions, we do not find that SFD overpredicts reddening by a large factor; rather, we find that SFD overpredicts reddening by about 14% in B − V, though, because of the reddening law adopted by SFD, this varies from color to color. The blue tip maps and measurements can be found at the Web site http://www.skymaps.info/bluetip
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