The Nuclear Reaction Waiting Points: 22 Mg, 26 Si, 30 S, and 34 Ar and Bolometrically Double-peaked Type I X-Ray Bursts

Type I X-ray bursts with a double peak in the bolometric luminosity have been observed from several sources. The separation between the two peaks is on the order of a few seconds. We propose a nuclear waiting point impedance in the thermonuclear reaction flow to explain these observations. Nuclear structure information suggests the potential waiting points: 22 Mg, 26 Si, 30 S, and 34 Ar, which arise in conditions, where a further reaction flow has to await a β + -decay, because the (α, p )-reaction is too weak to overcome the target Coulomb barrier and the ( p , γ)-reaction is quenched by photodisintegration at the burst temperature. The conclusion is that the effects of the experimentally unknown 30 S(α, p ) 33 Cl and 34 Ar(α, p ) 37 K might be directly visible in the observation of X-ray burst light curves.