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 $BVJH{K}_s(3.4\to 22)\mu m$ data for classical Cepheids and O-stars occupying the broader Galaxy. The apparent optical color-excess ratios vary significantly with Galactic longitude ($\ell$), whereas the near-infrared results are comparatively constant with $\ell$ and Galactocentric distance ($⟨E(J-\overline{3.5\mu m})/E(J-K_s)⟩=1.28\pm 0.03$). The results derived imply that classical Cepheids and O-stars display separate optical trends ($R_{V,BV}$) with $\ell$, 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 $⟨A_J/E(J-K_s)⟩=⟨R_{J,J{K}_s}⟩=1.49\pm 0.05$ ($⟨A_{K_s}/A_J⟩=0.33\pm 0.02$), 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 $⟨R_{V,BV}⟩\sim 3.1$ and $⟨R_{V,BV}⟩\sim 3.3$, respectively.

To appear in Astronomy and Astrophysics

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