Thermal emission from low-field neutron stars

We present a new grid of LTE model atmospheres for weakly magnetic ($B\la10^{10}$G) neutron stars, using opacity and equation of state data from the OPAL project and employing a fully frequency- and angle-dependent radiation transfer. We discuss the differences from earlier models, including a comparison with a detailed NLTE calculation. We suggest heating of the outer layers of the neutron star atmosphere as an explanation for the featureless X-ray spectra of RX J1856.5–3754 and RX J0720.4–3125 recently observed with Chandraand XMM.