2016A&A...593A.124M

Near-infrared color-excess and extinction ratios are essential for establishing the cosmic distance scale and probing the Galaxy, particularly when analyzing targets attenuated by significant dust. A robust determination of those ratios followed from leveraging new infrared observations from the VVV survey, wherein numerous bulge RR Lyrae and Type II Cepheids were discovered, in addition to BVJHKs(3.4-22)µm data for classical Cepheids and O stars occupying the broader Galaxy. The apparent optical color-excess ratios vary significantly with Galactic longitude (l), whereas the near-infrared results are comparatively constant with and Galactocentric distance (<E(J-3.5um)/E(J-K_s)≥1.28±0.03). The results derived imply that classical Cepheids and O stars display separate optical trends (R_V,BV) with , which appear to disfavor theories advocating a strict and marked decrease in dust size with increasing Galactocentric distance. The classical Cepheid, Type II Cepheid, and RR Lyrae variables are characterized by <A_J/E(J-Ks)≥<R_J,JKs≥1.49±0.05 (<A_Ks/A_J≥0.33±0.02), whereas the O stars are expectedly impacted by emission beyond 3.6µm. The mean optical ratios characterizing classical Cepheids and O stars are approximately <R_V,BV≳3.1 and <R_V,BV≳3.3, respectively.