Nucleosynthesis in white dwarf close encounters and collisions

Transcription

1 Nucleosynthesis in white dwarf close encounters and collisions Enrique García-Berro 1,2 Gabriela Aznar-Siguán 1,2 Pablo Lorén-Aguilar 1,2,3 Jordi José 1,2 Jordi Isern 2,4 1 Universitat Politècnica de Catalunya 2 Institut d Estudis Espacials de Catalunya 3 University of Exeter 2,4 Institut de Ciències de l Espai (CSIC)

2 Outline Introduction Motivation Smoothed Particle Hydrodynamics Results Conclusions

3 Outline Introduction Motivation Smoothed Particle Hydrodynamics Results Conclusions

4 Introduction Globular clusters are stellar systems of stars, have high core densities of around 10 3 pc -3 are old (have ages around Gyr), and contain many degenerate objects. Also, the central regions of galaxies have very high stellar densities. In such a dense environment stars can pass very close one to another. During the lifetime of the cluster every star will suffer one or more of these events. This leads to the formation of binaries through dynamical interactions and to the emission of gravitational waves.

5 Introduction It has been predicted that the white dwarf merger rate leading to super-chandrasekhar remnants will be increased by an order of magnitude through dynamical interactions (Shara & Hurley 2002).

6 Outline Introduction Motivation Smoothed Particle Hydrodynamics Results Conclusions

7 Motivation Most of the previous studies of this kind have been performed either with low resolution, incomplete physical prescriptions or with limited ranges of masses and chemical compositions. We have performed a series of high-resolution Smoothed Particle Hydrodynamics simulations of white dwarf interactions with three main objectives: 1. Compute their dynamical behavior. 2. Compute the associated nucleosynthesis. 3. Study the different kind of remnants as a function of the initial conditions.

8 Outline Introduction Motivation Smoothed Particle Hydrodynamics Results Conclusions

9 The SPH code Riemann Solver (Monaghan, 1995). Gravity: binary tree (Barnes & Hut, 1986). Polynomial kernel (Monaghan & Lattanzio, 1985). Predictor-corrector (Serna et al. 1996). We use particles. Energy and angular momentum conserved at 0.01% in 10 4 time steps. Helmholtz EOS, which includes: Electrons, Fermi-Dirac integrals. Ions: ideal plus Coulomb corrections. Photons.

10 The SPH code Full set of nuclear reactions: 12 C+ 12 C -chains from He to Zn He, CO and ONe secondaries. Neutrino losses (Itoh et al. 1996) MPI parallelization.

11 Outline Introduction Motivation Smoothed Particle Hydrodynamics Results Conclusions

12 Collisions: setup We have performed simulations of close encounters of two white dwarfs of different masses, screening a broad range of parameters. ω Star 1 y ini Star 2 x ini ω

13 Collisions: summary, 0.6 M M

14 Collisions: summary, full set

15 Collisions: summary, full set

16 Eccentric binary

17 Lateral collision: single remnant

18 Direct collision: disruption of both stars

19 Direct collision: disruption of one star

20 Outcomes: 0.6 M M

21 Outcomes: full set

22 No disruption

23 Disruption

24 Ejected mass

25 Debris mass

26 Accreted mass

27 Peak temperatures

28 Metallicity enhancement

29 Chemical abundances

30 Mass of 56 Ni synthesized

31 Outline Introduction Motivation Smoothed Particle Hydrodynamics Results Conclusions

32 Summary We have simulated the final state of a wide range of binary white dwarf close encounters. The result of such encounters can be either a merger or the formation of an eccentric double white dwarf. In the case of mergers can be a direct collision or a lateral one. In some cases we obtain detonations, which may lead to the disruption of one or both stars, to super-chandrasekhar Type Ia supernovae, or to sub-luminous supernovae. In all cases we have computed the associated nucleosynthesis.

33 Summary The masses of nickel synthesized have been quantified, as well as the nucleosynthetic pattern in those interactions in which no powerful explosion is obtained.

34 Nucleosynthesis in white dwarf close encounters and collisions Enrique García-Berro 1,2 Gabriela Aznar-Siguán 1,2 Pablo Lorén-Aguilar 1,2,3 Jordi José 1,2 Jordi Isern 2,4 1 Universitat Politècnica de Catalunya 2 Institut d Estudis Espacials de Catalunya 3 University of Exeter 2,4 Institut de Ciències de l Espai (CSIC)