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C/O abundance in white dwarf interior

C/O abundance in white dwarf interior. The asteroseismological data Need higher 12 C+a ? Different convective schemes The effect of 12 C+a So what?. White dwarf pulsations. Pulsation in WDs are non-radial g modes. The restoring force is g ravity.

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C/O abundance in white dwarf interior

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  1. C/O abundance in white dwarf interior • The asteroseismological data • Need higher 12C+a ? • Different convective schemes • The effect of 12C+a • So what?

  2. White dwarf pulsations Pulsation in WDs are non-radialg modes The restoring force is gravity

  3. Several pulsations with periods ranging between 100 and 3000 s

  4. The power spectrum

  5. Period spacing Mass, surface temperature Frequency splitting Rotation, magnetic field Nonuniformities Chemical stratification dP/dt Cooling rate PG 2131 Kawaler et al. 1995 Variable WDs as a tool

  6. The best case: GD 358 11 low degree (l=1, m=0) modes of consecutive radial overtone (k=8-18) with periods 400-800 s Metcalfe et al. 2001: XO = 0.84 ± 0.03 S300 = 370 ± 40 KeV b Metcalfe et al. 2002: S300 = 195 ± 15 KeV b Metcalfe 2003:

  7. A premature determination? Fontaine & Brassard 2002 Not enough information in the 11 periods available for GD358

  8. We don’t need higher 12C(a,g) Straniero et al. 2003 Kunz + semiconvection XO = 0.79

  9. Different convective schemes Straniero et al. 2003 Same nuclear reaction rate(Kunz et al. 2000) CM: classical model (no overshooting, no semi-convection) SCM-NoBP:semiconvection without breathing pulses SCM: semi-convection MOM: mechanical overshooting

  10. Straniero et al. 2003 Bare Schwarzschild Method XO = 0.56 Semiconvective Model XO = 0.79 High Overshoot Model XO = 0.56

  11. The effect of 12C(a,g) Straniero et al. 2003 A variation within Kunz error range yields a change of about DXO= ± 0.15

  12. Conclusions • Asteroseismology will determine with high accuracy XO • Standard model with Kunz 12C(a,g) is in reasonable agreement with seismic value • Uncertainty on 12C(a,g) imply uncertainty of about DXO= ± 0.15 • Differences on convection treatment are at the level of0.20 • Improvement on 12C(a,g) can provide significant information on convection.

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