16759

Extinction and polarization by interstellar dust taints astrophysical signals comma frustrating precision measurement of cosmological standard candles comma electromagnetic components of multimessenger transients comma and CMB signals. Understanding the origins of dust variations on small angular scales and along the line of sight in true three-dimensional detail comma as informed by local physical influences comma is now both possible and pressing. We propose STIS 1600-3100 A spectroscopy of five background stars probing a diffuse cloud irradiated by the O9.2IV star Zeta Oph comma the nearest (182 pc) high-UV environment. Our optical polarization measurements along these mid-latitude low-confusion sightlines reveal a B field aligned with 8-micron bright filaments. The ratio of polarization to color excess comma P-E(B-V) comma exceeds the empirical (Serkowski) limit of 9 comma indicating very efficient polarization and a high degree of grain alignment comma plausibly from spin-up by radiative torques. The optical-infrared data indicate a reddening curve characteristic of R_V=A_V-E(B-V)<2.4 comma a signature of extreme dust and a size distribution favoring small grains. With measurement of the near-UV reddening slope comma the height and width of the 2175 A bump comma and potentially the far-UV rise comma we will be able to forge a compelling association between extinction curve morphology comma polarization efficiency comma grain magnetic field alignment comma and the dominant radiative influence of a well-characterized hot star. Characterizing the extinction of high-polarization low-Rv PAH-emitting grains in this local laboratory promotes understanding the conditions that produce anomalous dust in AGN comma SNe comma GRBs comma and starbursts further afield.