UNIVERSALITY OF THE NEAR-INFRARED EXTINCTION LAW BASED ON THE APOGEE SURVEY

Abstract

Whether the near-infrared (NIR) extinction law is universal has long been a debated topic. Based on the APOGEE H-band spectroscopic survey, 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 advantage of this and using a sample of 5942 K-type giants, the NIR extinction law is carefully revisited. 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.