  Recent observations by XMM-Newton detected rotational pulsations in the total
brightness and spectrum of several neutron stars. To properly interpret the
data, accurate modeling of neutron star emission is necessary. Detailed
analysis of the shape and strength of the rotational variations allows a
measurement of the surface composition and magnetic field, as well as
constrains the nuclear equation of state. We discuss our models of the spectra
and light curves of two of the most observed neutron stars, RX J1856.5-3754 and
1E 1207.4-5209, and discuss some implications of our results and the direction
of future work.
