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Title: Reaction rate and composition dependence of the stability of thermonuclear burning on accreting neutron stars

The stability of thermonuclear burning of hydrogen and helium accreted onto neutron stars is strongly dependent on the mass accretion rate. The burning behavior is observed to change from Type I X-ray bursts to stable burning, with oscillatory burning occurring at the transition. Simulations predict the transition at a 10 times higher mass accretion rate than observed. Using numerical models we investigate how the transition depends on the hydrogen, helium, and CNO mass fractions of the accreted material, as well as on the nuclear reaction rates of 3α and the hot-CNO breakout reactions {sup 15}O(α, γ){sup 19}Ne and {sup 18}Ne(α, p){sup 21}Na. For a lower hydrogen content the transition is at higher accretion rates. Furthermore, most experimentally allowed reaction rate variations change the transition accretion rate by at most 10%. A factor 10 decrease of the {sup 15}O(α, γ){sup 19}Ne rate, however, produces an increase of the transition accretion rate of 35%. None of our models reproduce the transition at the observed rate, and depending on the true {sup 15}O(α, γ){sup 19}Ne reaction rate, the actual discrepancy may be substantially larger. We find that the width of the interval of accretion rates with marginally stable burning depends strongly on bothmore » composition and reaction rates. Furthermore, close to the stability transition, our models predict that X-ray bursts have extended tails where freshly accreted fuel prolongs nuclear burning.« less
Authors:
 [1] ;  [2] ;  [3]
  1. National Superconducting Cyclotron Laboratory, Department of Physics and Astronomy, and Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, MI 48824 (United States)
  2. National Superconducting Cyclotron Laboratory and Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, MI 48824 (United States)
  3. Monash Center for Astrophysics, School of Mathematical Sciences, Monash University, Vic 3800 (Australia)
Publication Date:
OSTI Identifier:
22356800
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 787; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; ACCRETION DISKS; ALPHA REACTIONS; FUELS; HYDROGEN; MASS; NEUTRON STARS; NEUTRONS; NUCLEAR REACTIONS; NUCLEOSYNTHESIS; OXYGEN 15 TARGET; REACTION KINETICS; SIMULATION; STABILITY; VARIATIONS; X RADIATION