  Neutron stars in close binary star systems often accrete matter from their
companion stars. Thermonuclear ignition of the accreted material in the
atmosphere of the neutron star leads to a thermonuclear explosion which is
observed as an X-ray burst occurring periodically between hours and days
depending on the accretion rate. The ignition conditions are characterized by a
sensitive interplay between the accretion rate of the fuel supply and its
depletion rate by nuclear burning in the hot CNO cycle and the rp-process. For
accretion rates close to stable burning the burst ignition therefore depends
critically on the hot CNO breakout reaction, O15(alpha,gamma)Ne19, that
regulates the flow between the hot CNO cycle and the rapid proton capture
process. Until recently, the O15(alpha,gamma)Ne19-reaction rate was not known
experimentally and the theoretical estimates carried significant uncertainties.
In this paper we perform a parameter study of the uncertainty of this reaction
rate and determine the astrophysical consequences of the first measurement of
this reaction rate. Our results corroborate earlier predictions and show that
theoretically burning remains unstable up to accretion rates near the Eddington
limit, in contrast to astronomical observations.
