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ASTEROSEISMOLOGY OF LATE STAGES OF STELLAR EVOLUTION. Gérard Vauclair Observatoire Midi-Pyrénées, Toulouse. Second COROT-BRASIL Workshop, November 5, 2005. Overview. 1- Pulsators in late stages of stellar evolution: their location in the HR diagram
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ASTEROSEISMOLOGY OF LATE STAGES OF STELLAR EVOLUTION Gérard Vauclair Observatoire Midi-Pyrénées, Toulouse 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
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 • KPD 0629-0016
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