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 TYPETEMPERATURE RANGE SURFACE COMPOSITION DOV or GW Vir KC,He,O DBV KHe DAV or ZZ Ceti KH Pulsation in WDs are non-radial g modes The restoring force is gravity

Several pulsations with periods ranging between 100 and 3000 s

The power spectrum

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

The best case: GD 358 Metcalfe et al. 2001:X O = 0.84 ± 0.03 Metcalfe et al. 2002: S 300 = 370 ± 40 KeV b Metcalfe 2003: S 300 = 195 ± 15 KeV b 11 low degree (l=1, m=0) modes of consecutive radial overtone (k=8-18) with periods s

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

We don’t need higher 12 C(  ) Straniero et al Kunz + semiconvection X O = 0.79

Different convective schemes 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 Straniero et al. 2003

Bare Schwarzschild Method Semiconvective Model High Overshoot Model X O = 0.56 X O = 0.79

The effect of 12 C(  ) A variation within Kunz error range yields a change of about  X O = ± 0.15 Straniero et al. 2003

Conclusions Asteroseismology will determine with high accuracy X O Standard model with Kunz 12 C(  ) is in reasonable agreement with seismic value Uncertainty on 12 C(  ) imply uncertainty of about  X O = ± 0.15 Differences on convection treatment are at the level of 0.20 Improvement on 12 C(  ) can provide significant information on convection.