1 / 17

Hydrodynamical Simulation of Detonations in Superbursts

This thesis explores the observational properties of X-ray bursts and superbursts, with a focus on the hydrodynamical simulation of detonations in superbursts. The study includes the development of a multi-D algorithm to model astrophysical detonations, and the investigation of the propagation phase of the combustion.

delam
Download Presentation

Hydrodynamical Simulation of Detonations in Superbursts

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. UNIVERSITE LIBRE DE BRUXELLES Hydrodynamical simulation of detonations in superbursts. Noël Claire(I.A.A., U.L.B.) Thesis advisors : M. Arnould (I.A.A., U.L.B.) Y. Busegnies (I.A.A., U.L.B.) In collaboration with : M. Papalexandris (U.C.L.) V. Deledicque (U.C.L.) A. El messoudi (I.A.A., U.L.B.) P. Vidal (L.C.D., Poitiers) S. Goriely (I.A.A., U.L.B.) 5th JETSET School on High Performance Computing in Astrophysics, January 8th - 13th 2008

  2. Observational properties of X-ray bursts and superbursts 2.7 h X-ray burst Superburst 40 s Lewin & al., Space Sci. Rev., 62, 223, 1993 Kuulkers, NuPhS, 132, 466, 2004 Lmax 1038 ergs s-1 Etot 1039 ergs tburst 10s – several min trec 5min - days Lmax 1038 ergs s-1 Etot 1042 ergs tburst several min – several hours trec years 2/12

  3. Thermonuclear model of X-ray burst Accretion He H/He rp-process stable unstable C (X < 0.1) + heavy ashes above Fe C Fe Strohmayer, Brown, ApJ, 566, 1045, 2002 Schatz & al., Nuclear physics A, 718, 247, 2003 3/12

  4. He He / H C/Fe C / Ru or N.S. N.S. Accretion stream Atmosphere ~ 105 g cm-3 H/He burning 10 m C/Fe/Ru 100 m ~ 109 g cm-3 N.S. Crust Thermonuclear model of superburst Thermally unstable ignition of 12C at densities of about 108 – 109 g cm-3 4/12

  5. All previous studies of superbursts are 1D, they correctly reproduce the total energy, peak luminosity, recurrence time, and duration of the superburst. But superbursts are multi-D phenomena !!! • Accretion is not uniform on the surface • Ignition conditions not reached at the same time everywhere Importance of the study of the propagation of the combustion Spitkovsky & al., ApJ, 566, 1018, 2002 Moreover the propagation phase has never been studied, even in 1D Weinberg & al. (ApJ Letters, 650, 119, 2006) suggest that the way of propagation of the combustion in superburst phenomena is a detonation. 5/12

  6. A new finite volume method, parallelised algorithm for modeling astrophysical detonations.(Noël & al., A&A, 470, 653, 2007) • - Finite volume method algorithm (MUSCL type) • Unsplit dimentionally • Time-splittingis included to be able to solve the very stiff nuclear network equations • (Strang J., SIAM J. Num. Anal. 5, 506, 1968). • - Parallel code (mpi) The equations:2 dimentional euler equations with a general astrophysical equation of state and a 13 species nuclear reaction network. 6/12

  7. - Astrophysical equation of state (tabulated): ions + radiation + electrons partially degenerate and partially relativistic+ electrons/positrons pairs The E.O.S. is not a gamma law We had to write an adapted Riemann solver based on Colella, Glaz, JCP,59,264,1985. L R - Nuclear reaction network: 13 species (4He, 12C, 16O,…, 56Ni) nuclear reaction network : 11 (a,g) reactions from 12C(a,g)16O to 52Fe(a,g)56Ni, the corresponding 11 photodesintegration reactions, 3 heavy-ions reactions : 12C(12C,a)20Ne, 12C(16O,a)24Mg and 16O(16O,a)28Si , and the triple alpha-reaction and its inverse. - Test case : Reactive shock tube P (g s-2 cm-1) 7/12 Comparaison with (Fryxell, Muller, Arnett, MPA 449,1989)

  8. Detonation in pure 12C at T = 108K and r = 108 g cm-3 • 1D steady-state calculations (ZND model) are made by A. El Messoudi • -characteristic time-scales of the detonation • - characteristic length-scales of the detonation • - reaction-zone structure • set the initial parameters and boundary conditions in the time-dependent calculations • allow to compare 1D time-dependent results with the steady-state solution Mass fractions 8/12

  9. Temperature Energy generation Velocity Density Pressure Temperature (in K), velocity (in cm s-1), density (in g cm-3) and pressure (in erg cm-3) profiles of a detonation front in pure 12C at T =108 K and r = 108 g cm-3 at time = 5 10-6 s. X is in cm. Nuclear energy generation (erg g-1 s-1) profile + same simulation in a mixture C/Fe:XC=0.3 XFe=0.7 9/12

  10. Detonation in a mixture 12C/96Ru (XC=0.1; XRu=0.9) at T = 108K and r = 108 g cm-3 Energy generation Temperature Density Nuclear reaction network extension: 9 species (64Ni, 68Zn,…, 96Ru) and 16 nuclear reactions are added : 8 (a,g) and the corresponding 8 (g,a) reactions. Effective rates are introduced in order to reproduce the energy production of a reference network of 14758 reactions on 1381nuclides. (a,g) and (g,a) rates: Energy production (erg g-1 ) Nuclear energy generation (erg g-1 s-1) , temperature (K), density (g cm-3) and mass fractions profiles. Z is the distance to the shock in cm. 10/12

  11. Effective (a,g) and (g,a) rates: Energy generation Temperature Density Nuclear energy generation (erg g-1 s-1) , temperature (K), density (g cm-3) and mass fractions profiles. Z is the distance to the shock in cm. Full network calculation + same simulation in a mixture :XC=0.2 XRu=0.8 11/12

  12. Conclusions • We have developed a multi-D algorithm able to study • astrophysical detonations with a nuclear reaction network • and an astrophysical equation of state. • Our algorithm is robust to test cases. • We have been able to simulate a detonation in conditions • representative of superbursts in pure He accretors and in • mixed H/He accretors. • - We have constructed a new reduced nuclear reaction network. • - Multi-D simulations are in progress. 12/12

  13. 1D simulation of the propagation of the detonation in inhomogeneous medium • Multi-D simulations He C Si Fe Ni He C S Fe Ni X X Perspectives Pure He detonation which goes through an Fe buffer Collision of two C detonations 12/13 Temperature

  14. Detonation on the neutron star surface Weinberg & al. (ApJ Letters, 650, 119, 2006) suggest that the way of propagation of the combustion in superburst phenomena is a detonation.Detonations are intrinsically multi-D phenomena. burned gas Small perturbationsdisturb the detonation front. The planar front is replaced by incidentshocks, transverse waves, and triple points. These high-pressure points trajectories give rise to the cellular pattern. shock Reaction zone Desbordes LCD-CNRS P. Vidal (LCD, Poitiers) 6/14

  15. Detonation in a mixture 12C/96Ru at T = 108K and r = 108 g cm-3 full network : 14758 reactions, 1381 nuclides net0 : l0 net1 : l0+ l1+l6 rmax(64Ni-96Ru) : l0+ l1+l6 +l0+ l1+l6 rmax(16O-96Ru) : l0+ l1+l6 +l0+ l1+l6 Nuclear reaction network extension: Reverse rates are estimated making use of the reciprocity theorem.

  16. Hydra : the new Scientific Computer Configuration at the VUB/ULB Computing Centre HP XC Cluster Platform 4000, composed of 32 nodes Nodes HP Proliant DL585, each composed of - 4 CPUs AMD Opteron dual-core @ 2.4 GHz - 32 GB RAM - 73 GB hard drive

  17. Same simulation in a mixture C/Fe:XC=0.3 XFe=0.7 Pure C : D = 1.3 109 cm s-1, produces mainly He C/Fe : D = 1.21 109 cm s-1, produces mainly Ni

More Related