The Optical to Infrared Extinction Law of Magellanic Clouds Based on Red Supergiants and Classical Cepheids

Abstract

Precise interstellar dust extinction laws are important to infer the intrinsic properties of reddened objects and correctly interpret observations. In this work, we attempt to measure the optical–infrared extinction laws of the Large and Small Magellanic Clouds (LMC and SMC) by using red supergiant (RSG) stars and classical Cepheids as extinction tracers. The spectroscopic RSG samples are constructed based on the APOGEE spectral parameters, Gaia astrometric data, and multiband photometry. We establish the effective temperature–intrinsic color relations for RSG stars and determine the color excess ratio (CER) E(λ − G RP)/E(G BP − G RP) for the LMC and SMC. We use classical Cepheids to derive base relative extinction . The results are 1.589 ± 0.014 and 1.412 ± 0.041 for the LMC and SMC. By combining CERs with , the optical–infrared extinction coefficients are determined for 16 bands. We adjust the parameters of R V -dependent extinction laws and obtain average extinction laws for the LMC and SMC of R V = 3.40 ± 0.07 and R V = 2.53 ± 0.10, respectively, which are consistent with Gordon et al. In the optical bands, the adjusted R V extinction curves agree with the observations with deviations less than 3%.