Universality of the Near-Infrared Extinction Law Based on the APOGEE Survey

Abstract

Whether the near-infrared (NIR) extinction law is universal has been a long debated topic. Based on the APOGEE H-band spectroscopic survey as a key project of SDSS-III, the intrinsic colors of a large number of giant stars are accurately determined from the stellar effective temperature. Taking this advantage and using a sample of 5942 K-type giants, the NIR extinction law is carefully re-visited. The color excess ratio E(J-H)/E(J-Ks), representative of the NIR extinction law, shows no dependence on the color excess when E(J-Ks) changes from ~0.3 to ~4.0, which implies a universal NIR extinction law from diffuse to dense regions. The constant value of E(J-H)/E(J-Ks), 0.64, corresponds to a power law index of 1.95. The other two ratios, E(H-Ks)/E(J-Ks) and E(J-H)/E(H-Ks), are 0.36 and 1.78 respectively. The results are consistent with the MRN dust size distribution.