AAS 205th Meeting, 9-13 January 2005
Session 83 Neutron Stars and Pulsars
Oral, Tuesday, January 11, 2005, 2:00-3:30pm, California

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[83.04] Ash Exposure and the Convective Extent in Radius Expansion X-ray Bursts

N. N. Weinberg (Caltech), L. Bildsten (KITP), A. Heger (LANL)

The convective region of the atmosphere during a Type I X-ray burst is well-mixed with the ashes of nuclear burning due to the short turbulent mixing time scale of the convection. We calculate the maximum vertical extent of the convective region during a radius expansion X-ray burst in order to determine whether some of the ashes of burning are ejected with the wind associated with the burst. We find that at its maximum extent as little as 0.2% of the total accreted mass lies above the convective region, depending on the burst ignition parameters such as the accretion rate, the composition of the accreted material, and the base column density. During a radius expansion burst as much as ~1% of the accreted mass is ejected in the wind associated with the super-Eddington flux. Some of the heavy elements produced during burning can therefore be expelled in the wind and may produce detectable rich emission line spectra. Our findings suggest that ashes as heavy as 28Si will be mixed in with the ejected material and possibly heavier elements if bursts ignite in the ashes of previous bursts as recent numerical simulations suggest (Woosley et al. 2004). The spectroscopic detection of ashes probes burst physics and might enable for gravitational redshift measurements.

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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.