AAS 207th Meeting, 8-12 January 2006
Session 198 Neutron Stars and Pulsars
Oral, Thursday, 10:00-11:30am, January 12, 2006, Balcony B

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[198.03] Magnetic Hydrogen Atmosphere Models and the Neutron Star RX~J1856.5-3754

W.C.G Ho, D.L. Kaplan (MIT Kavli Institute), P. Chang (UC Berkeley), M. van Adelsberg (Cornell), A.Y. Potekhin (Ioffe Physico-Technical Institute), G. Chabrier (Ecole Normale Supérieure de Lyon, CRAL)

RX~J1856.5-3754 is one of the brightest, nearby isolated neutron stars. Considerable resources have been devoted to its observation in an attempt to constrain realistic atmosphere models and measure spectral lines. While the multiwavelength spectrum is well-fit by a simple two-temperature blackbody model without any spectral features, this model can require an unphysically large radius (R\infty>20~km) and generally implies pulsations that have yet to be detected. Light element atmosphere models greatly overpredict the optical/UV flux, while heavy element atmosphere models predict a large number of unobserved spectral features in the X-ray regime. We show that our latest magnetic, partially ionized hydrogen atmosphere models can fit the entire spectrum, from X-rays to optical, of RX~J1856.5-3754. The model fit requires only a single temperature. We also calculate sample pulsations that are below the currently observed limits. The origin of the thin atmospheres required to fit the data is an important question, and we briefly discuss mechanisms for producing these atmospheres. Nevertheless, our model is the most self-consistent picture for explaining all the observations of RX~J1856.5-3754.

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