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)

(l =1, m=0) (l =2, m=0) (l =3, m=0)

http://asteroseismology.org/

Montgomery & Winget (1999)

Beyond Local Fitting

• Moore’s Law: Computing performance per unit cost doubles approximately every 18 months

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)

• 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

Sullivan et al. (in prep)

Metcalfe et al. (2005)

Winget et al. (1994)

EC 20058 (28400 K)

CBS 114 (26200 K)

GD 358 (24900 K)

More Stars

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

More Models

• 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 theoryMetcalfe (2005)

More Parameters

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/

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)

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

Althaus et al. (2005)

Grossman & Taam (1996)

More Dimensions

“3D models are wrong in three dimensions.” – Ed Nather

http://www.lcse.umn.edu/

The Future• We can use computers to generate millions of

simple models for comparison with observations.

• With similar resources, we can calculate a few complete evolutionary 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