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Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD

Edward F. Schlafly, Douglas P. Finkbeiner

TL;DR

The paper develops a spectrum-based method to measure interstellar dust reddening by predicting intrinsic stellar colors from SSPP parameters and MARCS atmospheres, then comparing with observed SDSS colors. By calibrating against high-latitude stars, the authors derive reddening coefficients R_a-b and color-color ratios, finding strong support for the Fitzpatrick 1999 reddening law with R_V=3.1 and a 14% recalibration of the SFD map. The results yield a calibrated reddening map that reproduces known features while highlighting regional normalization variations, and demonstrate the method’s robustness across stellar types and sky regions. The work lays groundwork for three-dimensional dust mapping using distance estimates and motivates cross-survey validation with Pan-STARRS and LAMOST data.

Abstract

We present measurements of dust reddening using the colors of stars with spectra in the Sloan Digital Sky Survey. We measure reddening as the difference between the measured and predicted colors of a star, as derived from stellar parameters from the SEGUE Stellar Parameter Pipeline (Lee et al. 2008a). We achieve uncertainties of 56, 34, 25, and 29 mmag in the colors u-g, g-r, r-i, and i-z, per star, though the uncertainty varies depending on the stellar type and the magnitude of the star. The spectrum-based reddening measurements confirm our earlier "blue tip" reddening measurements (Schlafly et al. 2010, S10), finding reddening coefficients different by -3%, 1%, 1%, and 2% in u-g, g-r, r-i, and i-z from those found by the blue tip method, after removing a 4% normalization difference. These results prefer an R_V=3.1 Fitzpatrick (1999) reddening law to O'Donnell (1994) or Cardelli et al. (1989) reddening laws. We provide a table of conversion coefficients from the Schlegel et al. (1998) maps of E(B-V) to extinction in 88 bandpasses for 4 values of R_V, using this reddening law and the 14% recalibration of SFD first reported by S10 and confirmed in this work.

Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD

TL;DR

The paper develops a spectrum-based method to measure interstellar dust reddening by predicting intrinsic stellar colors from SSPP parameters and MARCS atmospheres, then comparing with observed SDSS colors. By calibrating against high-latitude stars, the authors derive reddening coefficients R_a-b and color-color ratios, finding strong support for the Fitzpatrick 1999 reddening law with R_V=3.1 and a 14% recalibration of the SFD map. The results yield a calibrated reddening map that reproduces known features while highlighting regional normalization variations, and demonstrate the method’s robustness across stellar types and sky regions. The work lays groundwork for three-dimensional dust mapping using distance estimates and motivates cross-survey validation with Pan-STARRS and LAMOST data.

Abstract

We present measurements of dust reddening using the colors of stars with spectra in the Sloan Digital Sky Survey. We measure reddening as the difference between the measured and predicted colors of a star, as derived from stellar parameters from the SEGUE Stellar Parameter Pipeline (Lee et al. 2008a). We achieve uncertainties of 56, 34, 25, and 29 mmag in the colors u-g, g-r, r-i, and i-z, per star, though the uncertainty varies depending on the stellar type and the magnitude of the star. The spectrum-based reddening measurements confirm our earlier "blue tip" reddening measurements (Schlafly et al. 2010, S10), finding reddening coefficients different by -3%, 1%, 1%, and 2% in u-g, g-r, r-i, and i-z from those found by the blue tip method, after removing a 4% normalization difference. These results prefer an R_V=3.1 Fitzpatrick (1999) reddening law to O'Donnell (1994) or Cardelli et al. (1989) reddening laws. We provide a table of conversion coefficients from the Schlegel et al. (1998) maps of E(B-V) to extinction in 88 bandpasses for 4 values of R_V, using this reddening law and the 14% recalibration of SFD first reported by S10 and confirmed in this work.

Paper Structure

This paper contains 21 sections, 6 equations, 8 figures, 6 tables.

Table of Contents

  1. Introduction
  2. Data
  3. The SDSS
  4. The SSPP
  5. MARCS Model Atmospheres
  6. Selection Cuts
  7. Methods
  8. Results
  9. Performance at High Galactic Latitudes
  10. Calibration
  11. Reddening Map
  12. Discussion
  13. Fitting the Reddening in the SDSS Colors
  14. Fitting Ratios of $R_{a-b}$ using $\Delta_{}$ Color-Color Diagrams
  15. Sources of Systematic Error
  16. ...and 6 more sections

Figures (8)

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  • ...and 3 more figures