X-ray Spectroscopy of the 11 Minute LMXB 4U1820-30

The globular cluster LMXB 4U182030 consists of a neutron star and a Hedegenerate dwarf in an 11 minute binary. Based on existing Einstein OGS & SSSspectra, ASCA spectra, and an evolutionary model of 4U1820, we argue that theXray spectrum of this famous binary is the superposition of a strong continuumand the emission lines and recombination continua of a photoionized plasmawhich is strongly enhanced in light elements. XMM spectroscopy of 4U1820 willconstrain the relative abundances of this plasma and thereby strongly constrainthe evolutionary history the binary. The strengths and widths of the lines andrecombination continua will constrain the plasma emission measure distribution,electron temperature, optical depth, density, and radius of formation within truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]