The Optical to Mid-Infrared Extinction Law Based on the APOGEE, Gaia
  DR2, Pan-STARRS1, SDSS, APASS, 2MASS and WISE Surveys
  A precise interstellar dust extinction law is critically important to
interpret observations. There are two indicators of extinction: the color
excess ratio (CER) and the relative extinction. Compared to the CER, the
wavelength-dependent relative extinction is more challenging to be determined.
In this work, we combine spectroscopic, astrometric, and photometric data to
derive high-precision CERs and relative extinction from optical to mid-infrared
(IR) bands. A group of 61,111 red clump (RC) stars are selected as tracers by
stellar parameters from APOGEE survey. The multiband photometric data are
collected from Gaia, APASS, SDSS, Pan-STARRS1, 2MASS, and WISE surveys. For the
first time, we calibrate the curvature of CERs in determining CERs
E(lambda-GRP)/E(GBP-GRP) from color excess--color excess diagrams. Through
elaborate uncertainty analysis, we conclude that the precision of our CERs is
significantly improved (sigma < 0.015). With parallaxes from Gaia DR2, we
calculate the relative extinction A_GBP/A_GRP for 5051 RC stars. By combining
the CERs with the A_GBP/A_GRP, the optical--mid-IR extinction A_lambda/A_GRP
has been determined in a total of 21 bands. Given no bias toward any specific
environment, our extinction law represents the average extinction law with the
total-to-selective extinction ratio Rv=3.16+-0.15. Our observed extinction law
supports an adjustment in parameters of the CCM Rv=3.1 curve, together with the
near-IR power-law index alpha=2.07+-0.03. The relative extinction values of HST
and JWST near-IR bandpasses are predicted in 2.5% precision. As the observed
reddening/extinction tracks are curved, the curvature correction needs to be
considered when applying extinction correction.
