The Importance of15O(α,γ)19Ne to X‐Ray Bursts and Superbursts

One of the two breakout reactions from the hot CNOcycle is 15O(a,g)19Ne,which at low temperatures depends strongly on the resonance strength of the4.033 MeV state in 19Ne. An experimental upper limit has been placed on itsstrength, but the lower limit on the resonance strength and thereby theastrophysical reaction rate is unconstrained experimentally. However, thisbreakout reaction is crucial to the thermonuclear runaway which causes type IX-ray bursts on accreting neutron stars. In this paper we exploit astronomicalobservations in an attempt to constrain the relevant nuclear physics and deducea lower limit on the reaction rate. Our sensitivity study implies that if therate were sufficiently small, accreting material would burn stably withoutbursts. The existence of type I X-ray bursts and superbursts consequentlysuggests a lower limit on the 15O(a,g)19Ne reaction rate at low temperatures.Comment: 10 pages, 4 figures, uses apj.sty, accepted for publ. in Astrophys.