Hydrodynamic Models of Type I X-Ray Bursts: Metallicity Effects

Abstract

Type I X-ray bursts are thermonuclear stellar explosions driven by chargedparticle reactions. In the regime for combined H/He-ignition, the main nuclear flow is dominated by the rp-process (rapid proton-captures and β + -decays), the 3α-reaction, and the αp-process (a suite of (α,p) and (p,γ) reactions). The main flow is expected to proceed away from the valley of stability, eventually reaching the proton drip-line beyond A = 38. Detailed analysis of the relevant reactions along the main path has only been scarcely addressed, mainly in the context of parameterized one-zone models. In this paper, we present a detailed study of the nucleosynthesis and nuclear processes powering type I X-ray bursts. The reported 11 bursts have been computed by means of a spherically symmetric (1D), Lagrangian, hydrodynamic code, linked to a nuclear reaction network that contains 325 isotopes (from 1 H to 107 Te), and 1392 nuclear processes. These evolutionary sequences, followed from the onset of accretion up to the explosion and expansion stages, have been performed for 2 different metallicities to explore the dependence between the extension of the main nuclear flow and the initial metal content. We carefully analyze the dominant reactions and the products of nucleosynthesis, together with the the physical parameters that determine the light curve (including recurrence times, ratios between persistent and burst luminosities, or the extent of the envelope expansion). Results are in qualitative agreement with the observed properties of some well-studied bursting sources. Leakage from the predicted SbSnTe-cycle cannot be discarded in some of our models. Production of 12 C (and implications for the mechanism that powers superbursts), light p-nuclei, and the amount of H left over after the bursting episodes will also be discussed.

Absolute determination of theNa22(p,γ)Sallaska1, Wrede2, Garcı́a3 et al. 2011Phys. Rev. C255340View full textAdd to dashboardCite

“…The network used for additional reaction rates is the relevant subset of that used in Ref. [52]. The estimated 22 Na yields (mass-averaged mass fractions in the overall ejected shells) are listed in Table VI, which clearly shows that the impact of the central value of new rate roughly translates into lower 22 Na abundances by a factor up to ∼ 2 with respect to previous estimates.…”

Constraints on Bygone Nucleosynthesis of Accreting Neutron Stars

“…Schatz et al (2014), absent even-A nuclides, excluded by Meisel et al (2015); Deibel et al (2016b). Type I X-ray burst ashes from the multi-zone calculations from Cyburt et al (2016), as well as the last burst from models 1 and 2 of José et al (2010) are included for comparison. on models described in Keek et al (2012).…”

New Reaction Rates Of 64Ge(p,γ)65As(p,γ)66Se And The Impact On Type I X-ray Bursts

“…In recent reviews of XRB models [5,6,17,18,19], including post-processing model [18], onezone model [15,17], and multizone 1D hydrodynamic model [20], the reactions of 64 Ge(p,γ) 65 As and 65 As(p,γ) 66 Se are identified to have a critical impact on nucleosynthesis during XRBs. The last two models are fully self-consistent that consider the mutual influence of changes between nuclear energy generation and astrophysical condition [20].…”