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

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?

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

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

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

Charpinet et al.

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

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?

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

Bergeron, Fontaine, Brassard ZZ Ceti instability strip

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

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

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

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

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