X-ray Column Density towards the Low Mass X-ray Binary 4U 1702-429

We propose to use the RGS onboard XMMNewton to measure the Hydrogen columndensity towards the Xray binary 4U 1702429. We will detect and model the Ne,Mg, Si, Fe and O absorption edges in the RGS spectra of the source to determineinterstellar elemental abundances along the line of sight. We will convert theseabundances to an equivalent hydrogen column density in order to (i) remove asource of large uncertainty in modeling the continuum source spectra, and (ii)measure the distance to the Xray binary by employing a technique that comparesthe reddening of a source to that of red clump stars along the line of sight.Our ultimate goal is to combine the distance measurement with existing TypeIXray burst data to determine the mass and radius of the neutron star. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]