Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006head....9.0183c&link_type=abstract
American Astronomical Society, HEAD meeting #9, #1.83; Bulletin of the American Astronomical Society, Vol. 38, p.342
Astronomy and Astrophysics
Astronomy
Scientific paper
Type I X-ray bursts are thermonuclear explosions that occur on the surfaces of accreting neutron stars. Nearly all theoretical models of type I X-ray bursts, including sophisticated time-dependent models with large reaction networks, predict that bursts should occur for all accretion rates up to approximately the Eddington limit, whereas observations indicate that bursts do not occur for accretion rates above roughly 30% of the Eddington limit. We show that hydrogen burning via the temperature-independent hot CNO cycle, augmented by the extra CNO nuclei produced from stable helium burning, significantly lowers the temperature sensitivity of the total nuclear energy generation rate to such an extent as to suppress a thermonuclear runaway and hence a type I X-ray burst for accretion rates above roughly 30% of the Eddington limit. This result is consistent with observations. Furthermore, we show that, for relatively high trial reaction rates in theoretical models of the hot CNO cycle breakout reaction 15O(α,γ)19Ne, our model switches to a new regime in which bursts occur for all accretion rates up to approximately the Eddington limit. Since the latter regime disagrees with observations, we suggest that the true 15O(α,γ)19Ne reaction rate is lower than the fiducial rate of Caughlan & Fowler (1988).
Cooper Randall L.
Fisker Jacob Lund
Narayan Ramesh
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