The Blue Tip of the Stellar Locus: Measuring Reddening with the SDSS

TL;DR

This paper uses SDSS stellar colors to measure dust reddening, map dust distribution, and evaluate reddening laws, finding that the Fitzpatrick law with R_V=3.1 fits best and that SFD maps overestimate reddening.

Contribution

Introduces a blue tip method to measure reddening across the SDSS footprint, providing detailed dust maps and testing reddening laws against observations.

Findings

Favors Fitzpatrick (1999) reddening law with R_V=3.1

SFD dust map overestimates reddening by factors of 1.2 to 1.4

Identifies issues with SFD temperature correction in dusty regions

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.