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)

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

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

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

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

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

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

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

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

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

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

Recent highlights in white dwarf seismology

1) An enlightening review

Recent highlights in white dwarf seismology

2) Internal rotation profile and total angular momentum

Map of the internal rotation profile of PG 1159-035, the prototype of the GW Vir class of pulsating white dwarfs

Recent highlights in white dwarf seismology

3) An updated view of the ZZ Ceti instability strip

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)

Recent highlights in white dwarf seismology

5) Finally making sense of the GW Vir instability strip

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.

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

The ZZ Ceti instability strip

extended into the ELM regimePredicted spectrum of excited

dipole modes with TDC