Modeling spectral features from isolated neutron stars

We study several effects that influence the strength of the proton cyclotron and atomic features in the thermal spectra of magnetic neutron stars. Magnetic field variations over the neutron star surface leads to broadening of features. Vacuum polarization can strongly suppress spectral lines when B greater than or similar to 10(14) G. The surface spectrum is unaffected by vacuum polarization when B less than or similar to 7 x 10(13) G; thus the proton cyclotron absorption line (and atomic lines) can have a large equivalent width, possibly explaining the features seen in some isolated neutron stars.