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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.

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Presentation on theme: "Pulsations in White Dwarfs G. Fontaine Université de Montréal Collaborators: P. Brassard, P. Bergeron, P. Dufour, N. Giammichele (U. Montréal) S. Charpinet."— Presentation transcript:

1 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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4 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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6 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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8 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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10 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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12 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

13 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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15 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

16 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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18 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

19 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

20 Recent highlights in white dwarf seismology 1) An enlightening review

21 Recent highlights in white dwarf seismology 2) Internal rotation profile and total angular momentum

22 Map of the internal rotation profile of PG , the prototype of the GW Vir class of pulsating white dwarfs

23 Recent highlights in white dwarf seismology 3) An updated view of the ZZ Ceti instability strip

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25 Recent highlights in white dwarf seismology 4) Discovery of the 2 nd pulsating star massive enough to be partly solidified in its core (a ZZ Ceti star)

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27 Recent highlights in white dwarf seismology 5) Finally making sense of the GW Vir instability strip

28 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.

29 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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33 The ZZ Ceti instability strip extended into the ELM regime Predicted spectrum of excited dipole modes with TDC


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