pulsations in white dwarfs g. fontaine université de montréal collaborators: p. brassard, p....
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Pulsations in White Dwarfs
G. Fontaine
Université de Montréal
Collaborators:
P. Brassard, P. Bergeron, P. Dufour, N. Giammichele (U. Montréal)
S. Charpinet (U. Toulouse)
S. Randall (ESO, Garching)
V. Van Grootel (U. Liège)
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ZZ Cet stars
H-atmosphere (DA) white dwarfs (direct descendants of ~80% of post-AGB objects)
Low-degree (1,2), low- to mid-order g-mode pulsators
Opacity-driven (convective driving) due to recombination of H in the envelope
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V777 Her stars
He-atmosphere (DB) white dwarfs (cool descendants of ~20% of post-AGB objects)
Low-degree (1,2), low- to mid-order g-mode pulsators
Opacity-driven (convective driving) due to recombination of He in the envelope
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GW Vir stars
Mixed-atmosphere (PG1159) white dwarfs (immediate, very hot descendants of ~20% of post-AGB objects; He-C-O in roughly comparable proportions)
Low-degree (1,2), low- to mid-order g-mode pulsators
Opacity-driven (classical kappa-mechanism) due to opaque high ions of C and O in the envelope
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Hot DQV stars
Extremely rare (14 / 25,000) carbon-atmosphere white dwarfs discovered in 2007 only. They bunch around Teff~20,000 K and have very high surface gravities. They are likely all highly magnetic (>1 MGauss) and half them pulsate.
Low-degree (1,2), low- to mid-order g-mode pulsators
Opacity-driven (convective driving) due to recombination of C in the envelope
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ELM DAV
Rare, extremely low mass DA white dwarfs produced by common envelope evolution (post-RGB remnants)
Presumably low-degree (1,2), low- to mid-order g-mode pulsators discovered in 2012
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ELM DAV
Rare, extremely low mass DA white dwarfs produced by common envelope evolution (post-RGB remnants)
Presumably low-degree (1,2), low- to mid-order g-mode pulsators discovered in 2012
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Hot DAV stars
DA white dwarfs with very thin H envelopes. “DB’s disguised as DA’s”
Presumably low-degree (1,2), low- to mid-order g-mode pulsators
Presumably opacity-driven (kappa-mechanism or convective driving) due to recombination of He in the envelope
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Hot DAV stars
DA white dwarfs with very thin H envelopes. “DB’s disguised as DA’s”
Presumably low-degree (1,2), low- to mid-order g-mode pulsators
Presumably opacity-driven (kappa-mechanism or convective driving) due to recombination of He in the envelope
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DAOV stars
Low-mass, post-EHB DA stars predicted to pulsate
Low-degree (1,2), very low-order g-mode pulsators
Epsilon-mechanism due to H-shell burning at base of the H envelope
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DAOV stars
Low-mass, post-EHB DA stars predicted to pulsate
Low-degree (1,2), very low-order g-mode pulsators
Epsilon-mechanism due to H-shell burning at base of the H envelope
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Recent highlights in white dwarf seismology
1) An enlightening review
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Recent highlights in white dwarf seismology
2) Internal rotation profile and total angular momentum
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Map of the internal rotation profile of PG 1159-035, the prototype of the GW Vir class of pulsating white dwarfs
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Recent highlights in white dwarf seismology
3) An updated view of the ZZ Ceti instability strip
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Recent highlights in white dwarf seismology
4) Discovery of the 2nd pulsating star massive enough to be partly solidified in its core (a ZZ Ceti star)
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Recent highlights in white dwarf seismology
5) Finally making sense of the GW Vir instability strip
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Evolution of the predicted spectrum of excited dipole modes in an evolving model with a fixed PG1159 envelope composition (red dots), and that of a model in which stellar winds and gravitational settling are taken into account (black dots). The latter suggests that a GW Vir star (PG1159 spectral type) should again pulsate in its lifetime but, this time, as a much cooler DB white dwarf of the V777 Her type.
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dipole mode period spectrum,
n=1,38, early phases n=1,30, later phases
excited modes
blue edge
degeneracy boundary
base of atmosphere tau=100
Range of depth of
interest for driving by κ-mechanism
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The ZZ Ceti instability strip
extended into the ELM regimePredicted spectrum of excited
dipole modes with TDC