Constraining dust extinction properties via the VVV survey

摘要

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 BVJH K _(s)(3.4 → 22) μ m data for classical Cepheids and O stars occupying the broader Galaxy. The apparent optical color-excess ratios vary significantly with Galactic longitude ( ? ), whereas the near-infrared results are comparatively constant with ? and Galactocentric distance ( hbox{$langle E(J-overline{3.5~mu {m m}})/E(J-K_{m s}) angle =1.28,pm,0.03$} ). 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 ? K _(s))? = ? R _( J,J K _(s))? = 1.49 ± 0.05 ( ? A _( K _(s))/ A _( J )? = 0.33 ± 0.02 ), whereas the O stars are expectedly impacted by emission beyond 3.6 μ m . The mean optical ratios characterizing classical Cepheids and O stars are approximately ? R _( V,BV )? ~ 3.1 and ? R _( V,BV )? ~ 3.3 , respectively.