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Hydrogen Burning and Pulsations on Low Mass Helium Core White Dwarfs

Hydrogen Burning and Pulsations on Low Mass Helium Core White Dwarfs. Justin D. R. Steinfadt Lars Bildsten UCSB Wild Stars in the Wild West II 14th North American Workshop on Cataclysmic Variables and Related Objects March 16, 2009. Creating He-Core White Dwarfs. (Girardi et al. 2000).

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Hydrogen Burning and Pulsations on Low Mass Helium Core White Dwarfs

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  1. Hydrogen Burning and Pulsations on Low Mass Helium Core White Dwarfs Justin D. R. Steinfadt Lars Bildsten UCSB Wild Stars in the Wild West II 14th North American Workshop on Cataclysmic Variables and Related Objects March 16, 2009

  2. Creating He-Core White Dwarfs (Girardi et al. 2000) • C/O WDs • Truncation of the AGB • Helium WDs • Truncation of the RGB

  3. Two Possible Channels • Channel must prevent the core mass from growing beyond 0.45-0.48 M • Binary interaction via common envelope • Rapid mass loss via stellar winds induced by high metallicity

  4. Direct Evidence: ZZ Cetis • Thorough mode period analysis of pulsation spectrum is sensitive to: • Total Mass • Envelope Mass • Core Composition (courtesy Phil Arras)

  5. He-core ZZ Cetis (Steinfadt et al. 2008) • Low Mass WDs • PSR J0218+4232, PSR J1019+5307, PSR J1911-5958A • SDSS • J0022+00, J0022-10, J0822+27, J0849+04, J1053+52, J1056+65, J1234-02, J1426+01, J1436+50, J1630+42, J2252-00, J2345-01 • LP 400-22

  6. A Dichotomy in Evolution (Panei et al. 2007) (Panei et al. 2007) • 0.18 M represents a boundary between two very different classes of models • Highly dependent upon metallicity • Seen in the recent time-dependent evolution codes • Panei et al. 2001, 2007 • Serenelli et al. 2002 • Driebe et al. 1998

  7. A Dichotomy in Timescales

  8. Building a Hydrostatic Model • Envelope • Nuclear Energy Generation • PP - Chain • Pure Hydrogen composition • Radiative and convective heat transport Grey Atmosphere MENV Core Envelope Interface MWD • He Core • No energy generation • Isothermal • Pure Helium composition • Key Physics • MESA - Bill Paxton - http://mesa.sourceforge.net • EOS, Opacity, numerical algorithms, … • Diffusive equilibrium chemical profile • Two component plasma of Hydrogen, Helium and electrons

  9. pp Burning Slows Cooling 0 Gyr 0 Gyr 5 Gyr 5 Gyr 12 Gyr 12 Gyr

  10. pp Burning Slows Cooling 0 Gyr 0 Gyr 2 Gyr 2 Gyr 12 Gyr 12 Gyr

  11. Pulsation Probes H Shell • Non-adiabatic driving will determine where the ZZ Ceti Strip resides (ala Brickhill) • Epsilon mechanism may be possible with the pp burning shell • Period spacing would constrain the WD envelope mass. p-modes N2 c2kh2 g-modes (courtesy Phil Arras)

  12. Implications of a He-core WD Pulsator • New extension to the ZZ Ceti instability strip • New insights into the driving mechanisms • Constraints on He-core models through seismic modeling • Is there really a thick Hydrogen envelope? • Do low mass He-core WDs have nuclear burning envelopes?

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