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 BVJHK[subscript s](3.4 [right arrow] 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 ([left angle bracket]E(J - 3.5 [micrometre])/E(J-K[subscript s])[right angle bracket] = 1.28 [plus or minus] 0:03). The results derived imply that classical Cepheids and O stars display separate optical trends (R[subscript V,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 [left angle bracket]A[subscript J]/E(J - K[subscript s])[right angle bracket] = [left angle bracket]R[subscript J,JK[subscript s]][right angle bracket] = 1.49 [plus or minus] 0:05 ([left angle bracket]A[subscript K[subscript s]]/A[subscript J][right angle bracket] = 0.33 [plus or minus] 0.02), whereas the O stars are expectedly impacted by emission beyond 3.6 [micrometre]. The mean optical ratios characterizing classical Cepheids and O stars are approximately R[subscript V,BV] ~ 3.1 and R[subscript V,BV] ~ 3.3, respectively.