An Analysis of the Shapes of Interstellar Extinction Curves. VII. Milky Way Spectrophotometric Optical-through-Ultraviolet Extinction and Its R-Dependence

TL;DR

This study constructs 72 detailed interstellar extinction curves from optical to ultraviolet wavelengths for the Milky Way, analyzing their dependence on R(V) and revealing significant variability beyond this parameter.

Contribution

It provides a comprehensive, high-resolution set of extinction curves covering optical to UV wavelengths, and examines their R(V) dependence and intrinsic variability.

Findings

Extinction curves show R(V) dependence but also significant R(V)-independent variation.

High-resolution optical-UV data reveal structure at intermediate wavelengths.

Results enable better understanding of extinction effects on broad band systems.

Abstract

We produce a set of 72 NIR through UV extinction curves by combining new HST/STIS optical spectrophotometry with existing IUE spectrophotometry (yielding gapless coverage from 1150 to 10000 Angstroms) and NIR photometry. These curves are used to determine a new, internally consistent, NIR through UV Milky Way Mean Curve and to characterize how the shapes of the extinction curves depend on R(V). We emphasize that while this dependence captures much of the curve variability, there remains considerable variation which is independent of R(V). We use the optical spectrophotometry to verify the presence of structure at intermediate wavelength scales in the curves. The fact that the optical through UV portions of the curves are sampled at relatively high resolution makes them very useful for determining how extinction affects different broad band systems, and we provide several examples. Finally, we compare our results to previous investigations.