THE BLUE TIP OF THE STELLAR LOCUS: MEASURING REDDENING WITH THE SLOAN DIGITAL SKY SURVEY

Abstract

We present measurements of reddening due to dust using the colors of stars in\nthe Sloan Digital Sky Survey (SDSS). We measure the color of main sequence\nturn-off stars by finding the "blue tip" of the stellar locus: the prominent\nblue edge in the distribution of stellar colors. The method is sensitive to\ncolor changes of order 18, 12, 7, and 8 mmag of reddening in the colors u-g,\ng-r, r-i, and i-z, respectively, in regions measuring 90' by 14'. We present\nmaps of the blue tip colors in each of these bands over the entire SDSS\nfootprint, including the new dusty southern Galactic cap data provided by the\nSDSS-III. The results disfavor the best fit O'Donnell (1994) and Cardelli et\nal. (1989) reddening laws, but are well described by a Fitzpatrick (1999)\nreddening law with R_V = 3.1. The SFD dust map is found to trace the dust well,\nbut overestimates reddening by factors of 1.4, 1.0, 1.2, and 1.4 in u-g, g-r,\nr-i, and i-z, largely due to the adopted reddening law. In select dusty regions\nof the sky, we find evidence for problems in the SFD temperature correction. A\ndust map normalization difference of 15% between the Galactic north and south\nsky may be due to these dust temperature errors.\n

Affiliated Institutions

• Harvard University US
• Center for Astrophysics Harvard & Smithsonian US
• New York University US
• Lawrence Berkeley National Laboratory US
• University of Washington US
• Princeton University US

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