The Optical to Infrared Extinction Law of Magellanic Clouds Based on Red Supergiant and Classical Cepheid

TL;DR

This study measures the optical-infrared extinction laws of the Magellanic Clouds using red supergiants and Cepheids, providing precise extinction coefficients and Rv values to improve understanding of interstellar dust properties.

Contribution

It introduces a new method combining RSGs and Cepheids to accurately determine the extinction laws in the Magellanic Clouds, refining previous models.

Findings

Derived extinction coefficients for 16 bands.

Established Rv values of 3.40 for LMC and 2.53 for SMC.

Achieved less than 3% deviation in optical extinction curves.

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 multi-band photometry. We establish the effective temperature--intrinsic color relations for RSG stars and determine the color excess ratio (CER) E(lambda-GRP)/E(GBP-GRP) for LMC and SMC. We use classical Cepheids to derive base relative extinction A_GRP/E(GBP-GRP). The results are 1.589+-0.014 and 1.412+-0.041 for LMC and SMC. By combining CERs with A_GRP /E(GBP-GRP), the optical--infrared extinction coefficients A_lambda/A_GRP are determined for 16 bands. We adjust the parameters of Rv-dependent extinction laws and obtain the average extinction law of LMC and SMC as Rv=3.40+-0.07 and Rv=2.53+-0.10, which are consistent with Gordon et al. (2003). In the optical bands, the adjusted Rv extinction curves agree with the observations with deviations less than 3%.