Constraining dust extinction properties via the VVV survey

Abstract

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) mu m 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 l and Galactocentric distance (E(J-(3.5 mu m) over bar /E(J - K-s) = 1.28 +/- 0.03. The results derived imply that classical Cepheids and O stars display separate optical trends (R-V,R-BV) with l, 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-K-s) = (R-J,R-JKs) = 1.49 +/- 0.05 ((A(Ks)/A(J)) = 0.33 +/- 0.02), whereas the O stars are expectedly impacted by emission beyond 3.6 mu m. The mean optical ratios characterizing classical Cepheids and O stars are approximately (R-V,R-BV) similar to 3.1 and (R-V,R-BV) similar to 3.3, respectively.