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Session 92 - Pulsars.
Oral session, Wednesday, January 15
Harbour C,

[92.04] Magnetized Iron Atmospheres for Neutron Stars

M. Rajagopal, R. W. Romani (Stanford U.), M. C. Miller (U. Chicago)

Pulsar surface temperatures deduced from soft X-ray observations have important consequences for neutron star physics and the equation of state at supernuclear densities. It has been recognized, however, that inferred temperatures depend sensitively on the unknown composition of the neutron star surface. Motivated by recent low resolution spectra from ROSAT and by future missions such as XMM and AXAF, we have estimated the atomic properties of iron in magnetic fields B \sim 10^13G. and used these data to compute model atmospheres and emergent spectra. Magnetic Fe energy levels and photon cross sections are estimated using a Hartree-Fock formalism. Computing ionization equilibrium and normal mode opacities with these data, we construct our LTE atmospheres at 5.5 < Log(T_eff)< 6.5 and compute emergent spectra. We examine the dependence of the emergent spectra on T_eff and B. We also show the spectral variation with the angle between the magnetic field and the atmosphere normal and describe the significant limb darkening in the X-ray band. These results complement the authors' low field model atmospheres for light and heavy elements using detailed opacities. We also compare with other authors' recent detailed computations of neutron star H model atmospheres in high fields. The broad spectral differences for different surface compositions may be discernible with present X-ray data; we also note improvements needed to allow comparison of Fe models with future high quality spectra.

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