X Per: The Template Sightline for the Diffuse Interstellar Medium

Galactic interstellar dust is ubiquitous, but many aspects of the grains are notwell known. Current model constraints, based on IRUV data and assumed elementalabundances, are insufficient, as a plethora of viable models exist. Even theabundances are not well known; modelers must use proxies in the absence ofdirect measurements for the diffuse interstellar medium (ISM). Recent revisionsof these proxy values have only added to confusion over which is the bestrepresentative for the diffuse ISM, and highlighted the need for directmeasurements from the ISM itself. We will measure the O, Mg, Fe, and Siabundances along one sightline, to X Per, with the XMMNewton RGS, and use themwith our multiwavelength data for this sightline to construct a tightlyconstrained, realistic grain model. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]