Helium ignition on accreting neutron stars with a new triple-α reaction rate
We investigate the effect of a new triple-α reaction rate from Ogata et al. on helium ignition conditions on accreting neutron stars and on the properties of the subsequent type I X-ray burst. We find that the new rate leads to significantly lower ignition column density for accreting neutron stars at low accretion rates. We compare the results of our ignition models for a pure helium accretor to observations of bursts in ultracompact X-ray binaries (UCXBs), which are believed to have nearly pure helium donors. For ^._m > 0.001 ^._m_(Edd), the new triple-α reaction rate from Ogata et al. predicts a maximum helium ignition column of ~3 × 10^9 g cm^(−2), corresponding to a burst energy of ~4 × 10^(40) erg. For ^._m ~ 0.01 ^._m_(Edd) at which intermediate long bursts occur, the predicted burst energies are at least a factor of 10 too low to explain the observed energies of such bursts in UCXBs. This finding adds to the doubts cast on the triple-α reaction rate of Ogata et al. by the low-mass stellar evolution results of Dotter & Paxton.
Additional Information© 2010 American Astronomical Society. Received 2010 August 19; accepted 2010 October 1; published 2010 November 17. It is a pleasure to thank Edward Brown for helpful comments which improved the paper. We thank Evan O'Connor, Hendrik Schatz and James Truran for useful discussions and comments. We thank the anonymous referee for helpful suggestions. We also thank Kazuyuki Ogata for providing us with his triple- α reaction rates. This work is partially supported through NSF grants AST-0855535 and OCI-0905046.
Published - Peng2010p12236Astrophys_J.pdf