1 / 23

ASTEROSEISMOLOGY OF LATE STAGES OF STELLAR EVOLUTION

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

huslu
Télécharger la présentation

ASTEROSEISMOLOGY OF LATE STAGES OF STELLAR EVOLUTION

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. ASTEROSEISMOLOGY OF LATE STAGES OF STELLAR EVOLUTION Gérard Vauclair Observatoire Midi-Pyrénées, Toulouse 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?

  3. 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

  4. 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

  5. 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

  6. Charpinet et al.

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

  8. 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?

  9. 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

  10. Bergeron, Fontaine, Brassard ZZ Ceti instability strip

  11. sdB and COROT • Two long period sdBV for short runs • KPD 0716+0258 • KPD 0629-0016

  12. 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

  13. 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

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

  15. 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

More Related