2006ApJ...648L.123C

We investigate the effect of the hot CNO cycle breakout reaction ¹⁵O(α,γ)¹⁹Ne on the occurrence of type I X-ray bursts on accreting neutron stars. For f_rp≲0.1, where f_rpis a dimensionless factor by which we multiply the ¹⁵O(α,γ)¹⁹Ne reaction rate of Caughlan & Fowler, our model predicts that bursts should occur only for accretion rates M{dot} below a critical value ~0.3M{dot}_Edd. This agrees with observations. For larger values of f_rp, including the standard choice f_rp=1, the model switches to a new regime in which bursts occur all the way up to M{dot}~M{dot}_Edd. Since the latter regime disagrees with observations, we suggest that the true ¹⁵O(α,γ)¹⁹Ne reaction rate is lower than usually assumed.