C/O abundance in white dwarf interior
description
Transcript of C/O abundance in white dwarf interior
C/O abundance in white dwarf
interior
• The asteroseismological data• Need higher 12C+a ?• Different convective schemes • The effect of 12C+a• So what?
White dwarf pulsationsTYPE TEMPERATURE
RANGESURFACE
COMPOSITION
DOV or GW Vir
80000-180000 K C,He,O
DBV 22400-27800 K He
DAV or ZZ Ceti
11000-13000 K H
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 fieldFrequency splitting
PG 2131 Kawaler et al.
1995
Nonuniformities Chemical stratification
dP/dt Cooling rate
The best case: GD 358
Metcalfe et al. 2001: XO = 0.84 ± 0.03
Metcalfe et al. 2002:S300 = 370 ± 40 KeV b
Metcalfe 2003: S300 = 195 ± 15 KeV b
11 low degree (l=1, m=0) modes of consecutiveradial overtone (k=8-18) with periods 400-800 s
A premature determination?Fontaine & Brassard 2002
Not enough information
in the 11 periods availablefor GD358
We don’t need higher 12C()
Straniero et al. 2003
Kunz + semiconvection
XO = 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
Straniero et al. 2003
Bare Schwarzschild Method
Semiconvective Model
High Overshoot Model
XO = 0.56
XO = 0.56
XO = 0.79
The effect of 12C()
A variation within Kunz error range yields a change of about XO= ± 0.15
Straniero et al. 2003
Conclusions
• Asteroseismology will determine with high accuracy XO
• Standard model with Kunz 12C() is in reasonable agreement with seismic value
• Uncertainty on 12C() imply uncertainty of about XO= ± 0.15
• Differences on convection treatment are at the level of 0.20
• Improvement on 12C() can provide significant information on convection.