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The Future of White Dwarf Asteroseismology

The Future of White Dwarf Asteroseismology. Travis Metcalfe (NCAR). NGC 1514 – Crystal Ball Nebula. Kawaler & Dahlstrom (2000). Elsworth & Thompson (2004). http://asteroseismology.org/. ( l =1, m=0). ( l =2, m=0). ( l =3, m=0). Montgomery & Winget (1999). Beyond Local Fitting.

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The Future of White Dwarf Asteroseismology

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  1. The Future of White Dwarf Asteroseismology Travis Metcalfe (NCAR) NGC 1514 – Crystal Ball Nebula

  2. Kawaler & Dahlstrom (2000)

  3. Elsworth & Thompson (2004)

  4. http://asteroseismology.org/ (l=1, m=0) (l =2, m=0) (l =3, m=0)

  5. Montgomery & Winget (1999)

  6. Beyond Local Fitting • Moore’s Law: Computing performance per unit cost doubles approximately every 18 months

  7. Beyond Local Fitting • Moore’s Law: Computing performance per unit cost doubles approximately every 18 months • More is Better Law: If you spend more time writing the paper than running the models, you didn’t run enough models Metcalfe & Nather (1999)

  8. More Stars EC 20058 (28400 K) Sullivan et al. (in prep) • DBV stars are thought to evolve from H-deficient post-AGB stars (He/C/O) • He diffuses to the surface over time, growing thicker as the star gets cooler • From several DBVs with different temperatures we can calibrate the theory CBS 114 (26200 K) Metcalfe et al. (2005) GD 358 (24900 K) Winget et al. (1994)

  9. More Models Napiwotzki et al. (1999) Beauchamp et al. (1999) • Parallel genetic algorithm optimizes 4 parameters to model each DBV star • 0.45 < M* < 0.95 Msun 20000 < Teff < 30000 K 10-4 < Menv < 10-2 M* 10-7 < MHe < 10-5 M* • Pure C core out to 0.95 fractional mass point

  10. More Parameters • Results: reasonable fits for M* and Teff ; qualitative agreement with theory • Extension: add realistic adjustable C/O profile to model core structure • Application to CBS 114: agrees with the expected nuclear burning history and diffusion theory Metcalfe (2005)

  11. Beyond the Spherical Cow • Global exploration of relatively simple models has some limitations • How else might we use our continually expanding computational potential? • Another approach: build the best physical models, but limit the exploration http://www.moonjam.com/

  12. More Physics • Time-dependent diffusion calculations for evolution of H and He layers • Chemical profile of O/Ne models from repeated C-burning shell flashes • Self-consistent treatment of phase separation during C/O crystallization Corsico et al. (2004)

  13. More History • Complete evolution from ZAMS, through mass-loss on AGB, to WD regime • 5 chemical time steps for each evolutionary step; 70,000 models in total • Double-diffusive mixing- length theory for fluid with composition gradients Grossman & Taam (1996) Althaus et al. (2005)

  14. More Dimensions http://www.lcse.umn.edu/ “3D models are wrong in three dimensions.” – Ed Nather

  15. The Future • We can use computers to generate millions of simple models for comparison with observations. • With similar resources, we can calculate a few completeevolutionary tracks using relatively sophisticated physical models. • As computers get faster, they will allow us to generate millions of complete evolutionary models, opening the door to new tests of fundamental physics in white dwarf stars. IBM Bluegene/L system

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