Transcript Pulsations in White Dwarfs

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 postAGB 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) carbonatmosphere 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 midorder 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 midorder 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.
blue edge
base of atmosphere
tau=100
dipole mode period
spectrum,
n=1,38, early phases
n=1,30, later phases
degeneracy boundary
excited modes
Range of
depth of
interest for
driving by κmechanism
The ZZ Ceti instability strip
extended into the ELM regime
Predicted spectrum of excited
dipole modes with TDC