Publications of the Astronomical Society of the Pacific
111: 63-75, 1999


CORRECTING FOR THE EFFECTS OF INTERSTELLAR EXTINCTION

Edward L. Fitzpatrick

Department of Astronomy and Astrophysics, Villanova University, Mendel Hall, Villanova, PA 19085


ABSTRACT. This paper addresses the issue of how best to correct astronomical data for the wavelength-dependent effects of Galactic interstellar extinction. The main general features of extinction from the IR through the UV are reviewed, along with the nature of observed spatial variations. The enormous range of extinction properties found in the Galaxy, particularly in the UV spectral region, is illustrated. Fortunately, there are some tight constraints on the wavelength dependence of extinction and some general correlations between extinction curve shape and interstellar environment. These relationships provide some guidance for correcting data for the effects of extinction. Several strategies for dereddening are discussed along with estimates of the uncertainties inherent in each method. In the Appendix, a new derivation of the wavelength dependence of an average Galactic extinction curve from the IR through the UV is presented, along with a new estimate of how this extinction law varies with the parameter R ident A (V) / E (B - V). These curves represent the true monochromatic wavelength dependence of extinction and, as such, are suitable for dereddening IR-UV spectrophotometric data of any resolution, and can be used to derive extinction relations for any photometry system.


KEY WORDS: ISM: dust, extinction


Table of Contents

INTRODUCTION

SPATIAL VARIATIONS IN GALACTIC EXTINCTION
Variations Abound . . .
. . . But There is Some Order Amid the Chaos

CORRECTING FOR THE EFFECTS OF EXTINCTION
Using a Global Mean Curve
Using a R-Dependent Mean Curve
Using a Sightline-Specific Curve

FINAL COMMENTS

APPENDIX
Deriving a R-Dependent IR-through-UV Extinction Curve
The UV Region
The Optical/IR Region
The Full R-Dependent Curve

REFERENCES

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