The Optical to Mid-Infrared Extinction Law--An Adjustment to the Classic Rv = 3.1 Extinction Law

The appropriate estimation and correction of extinction is critically important to interpret observations. With Gaia Data Release 2 (DR 2), we can determine the color excess ratios (reddening law) and the extinction ratios (extinction law) in high precision. We combine photometric, spectroscopic, and astrometric data to investigate the reddening and extinction law from optical to mid-infrared bands based on red clump stars. The Gaia bands are adopted as basis bands in determining color excess ratios and extinction ratios in a total of 21 bands. To better describe our observed extinction law, we adjust parameters of the classical R_V = 3.1 curve, together with the near-IR power-law index \(\alpha = {2.07 \pm 0.03}\). After analyzing the possible variations of color excess ratios, we concluded that based on the APOGEE sample, the extinction law is universal within 4 kpc and A_V < 6 mag.