Probing the Properties of Interstellar Dust Towards the Hot Star Zeta Ophiuchi

Microscopic dust grains permeate the interstellar medium, blocking and obscuring light from all sources. This effect is termed interstellar extinction. Varying amounts and sizes of dust cause different amounts of extinction at different wavelengths of light which can be probed through the total amount of extinction, Av, an indicator for the amount of dust, and Rv, an indicator for the size of the dust. In order to characterize the dust and construct the reddening curves in a known dusty region, we obtained Hubble Space Telescope Space Telescope Imaging Spectrograph ultraviolet spectra for five bright stars lying behind the highly irradiating hot star Zeta Ophiuchi. Combining these spectra with archival photometric data, the extinction curves for each star in the sample are constructed and the best fit parameters calculated. Best fit models show interstellar average Rv~3.0  for Zeta Ophiuchi and a significantly lower Rv~2.3 for the target stars, indicating non-standard small dust grains. Such small dust grains are likely due to high levels of irradiation, systematically lowering the average dust grain size.