Constraining Dust Extinction Properties via the VVV Survey
  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 $BVJHK_{s}(3.4\rightarrow22)\mu m$ 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 ($\langle E(J-\overline{3.5\mu m})/E(J-K_s) \rangle =1.28\pm0.03$).
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 $\langle A_{J}/E(J-K_s) \rangle = \langle
R_{J,JK_s} \rangle =1.49\pm0.05$ ($\langle A_{K_s}/A_J \rangle =0.33\pm0.02$),
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 $\langle R_{V,BV} \rangle \sim3.1$ and $\langle R_{V,BV} \rangle
\sim3.3$, respectively.
