1. ASTEROSEISMOLOGY OF LATE STAGES OF STELLAR EVOLUTION
Gérard Vauclair
Observatoire Midi-Pyrénées, Toulouse
Beijing Normal University, October 13th, 2005
Second COROT-BRASIL Workshop, November 5, 2005

2. Overview
1- Pulsators in late stages of stellar evolution: their location in the HR diagram
2- the precursors to the white dwarf cooling sequence:
a) the AGB-PN channel: PNNV and PG1159
b) the EBHB-sdB channel: sdBV
3- the white dwarf pulsators: DBV, DAV
4- What can be done with COROT?

4. PNNV and PG1159 (GW Vir) pulsators
PNNV: central stars PG1159 spectral type
He, C, O (+H in ‘hybrid-PG1159)
PN, ongoing mass-loss
PG1159 pulsators: no PN , ongoing mass-loss
Teff: [170 kK – 80 kK]; log g:[6 -8]
Periods: ~3000 s - ~400 s, g-modes
Instability: K-mechanism C,O
Pulsators and non-pulsators mixed
Structure: C/O core, He/C/O enveloppe
Gravitational settling : He vs C/O?
Evolution from PG1159 to DB

5. Seismic diagnostic in white dwarfs
g-modes : f< Braunt-Vaisala and < Lamb
In wd Braunt-Vaisala decreases towards interior:
homogeneous composition : uniform period spacing
total mass determination
stratification :deviation from uniform period spacing, mode trapping
reflexion of waves with nodes at transition zones
fractional mass above transition zones
rotational splitting = rotation period

7. Subdwarf B pulsators Two classes:
Short period variables (spv or EC14026)
periods [~80 s - ~600 s]; p-modes
Long period variables (lpv or ‘Betsy stars’)
periods: hours; g-modes
Instability: Fe accumulation by diffusion
opacity bump = K-mechanism
works for both spv and lpv
Pulsators and non-pulsators mixed

8. Charpinet et al.

9. Sample of sdB light curves from CFHT (Fontaine, Charpinet)

11. White dwarf pulsators: the DBVs
DBV: Helium white dwarfs; 8 pulsators
Teff: 25kK– 20 kK (depends on H:He)
Instability: K-mechanism of He
Diffusion equilibrium not reached
Layered composition: He/He-C-O in envelope
He-C-O/C-O envelope – core
C/O in the core
Signature of core chemical composition and profile
in the period distribution?

13. White dwarf pulsators: the DAVs (ZZ Ceti)
DAV: H envelope: ~100 pulsators (~60 from SLOAN)
Periods: 70 s – 1500 s
Diffusion equilibrium almost achieved:
C/O core, He layer, H envelope
Instability: K-mechanism H in hot DAV +
Convective driving in cool DAV
Instability strip: Teff [~12500 K - ~11000 K]; pure?
Core composition, M, H mass fraction, rotation
DA models, cosmochronology

14. Bergeron, Fontaine, Brassard
ZZ Ceti instability strip

15. sdB and COROT Two long period sdBV for short runs KPD 0716+0258

17. White dwarfs with COROT
WD catalogues: 3000, 80% DA, 4% DAV
Only 15 with V<16 in GC
“” 13 “” “” in GAC
None is a pulsator
WD (V<16) surface density (high b)
~2 x 10**-3/sq.deg (PG, SDSS)
WD density in Gal. plane? x 10, x 15?
A few ZZ Ceti (V<16) expected in COROT exo fields

19. White Dwarf Rotation Angular Momentum evolution: the end
rotation periods distribution: constraint on angular momentum evolution
from ground-based multisite astero:
rotation periods between ~0.5 and ~2 days
but: observational bias against slow rotators
COROT: potential slow rotators accessible

22. Amplitude variations Commun in all WD pulsators non linear effects?
characteristic time scales?
COROT: continuous 150 days photometry

23. Conclusions Asteroseismology constraints on:
Fundamental parameters of white dwarfs and their progenitors ; internal structure and stratification
p-modes and g-modes in sdBs: better understanding of the HB
g-modes in white dwarfs:constraints on physical processes
- in previous evolution (mass loss, angular momentum, convection, overshooting..)
- ongoing along the cooling sequence (convection, gravitational settling, crystallization…)
better models for cosmochronology