A Tale of Three Dust Populations: Variable \(R_{\rm{V}}\) and Extreme Polarization Along Sightlines Toward \(\zeta\) Ophiuchi

Dust permeates the interstellar medium, reddening and polarizing background starlight, but dust properties vary with local environment. In order to characterize dust in a highly irradiated diffuse cloud, we measure the reddening and optical polarization towards 27 stars surrounding the mid-latitude \(b\)=\(+\)24\(^{\circ}\) O9.2IV star \(\zeta\) Ophiuchi, using new optical spectroscopy and polarimetry. We incrementally deredden and depolarize with distance, allowing us to distinguish dust components along these sightlines. The data indicate three distinct dust populations: a foreground component characteristic of average Milky Way dust ($R_{\rm{V}}$$\approx\(3.1, \)d$$\lesssim\(180 pc), a highly polarizing mid-distance component in the vicinity of \)\zeta\( Oph (\)R_{\rm{V}}$$\approx\(2.4, 200 pc\)