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 \rightarrow 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 ( \langle E ( J - \overline { 3.5 \mu m } ) / E ( J - K _ { s } ) \rangle = 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 \langle A _ { J } / E ( J - K _ { s } ) \rangle = \langle R _ { J,JK _ { s } } \rangle = 1.49 \pm 0.05 ( \langle A _ { K _ { s } } / A _ { J } \rangle = 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 \langle R _ { V,BV } \rangle \sim 3.1 and \langle R _ { V,BV } \rangle \sim 3.3 , respectively .