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

Abstract

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: 22Mg, 26Si, 30S, and 34Ar, 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 30S(α, p)33Cl and 34Ar(α, p) 37K might be directly visible in the observation of X-ray burst light curves.