Determination of basic neutron star parameters from spectral modeling of X-ray bursters

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Measuring neutron star (NS) radii and masses is an essential tool to investigate the properties of matter at super-nuclear densities. Thermal emission during thermonuclear X-ray bursts from NSs in low-mass X-ray binaries provides a unique opportunity to determine NS parameters, because of the high fluxes, large luminosity variations and the related changes in the spectral properties. We introduced the cooling tail method that uses hot NS atmosphere models to convert the observed spectral evolution during cooling stages of X-ray bursts to the Eddington flux and the stellar angular size. These are then translated to constraints on mass and radius. In this project we will investigate and eliminate systematic uncertainties which can potentially affect the results, namely the effects of stellar rotation and atmosphere expansion during the burst. We will also explore a new approach to constrain NS parameters.