1. Massive Pulsating White Dwarf Stars Barbara G. Castanheira S. O. Kepler, D. Winget, J.J. Hermes, K. Bell, … University of Texas at Austin McDonald Observatory

2. DQV

3. SDSS: ~ 30,000 new white dwarf stars Comparison between spectra and model grid Extended model grid with log g up to 10 (Koester 2010) Spectra is flux calibrated Adjust low order polynomial Use 5 SDSS colors in the fit

4. Runaway effect for DA white dwarf stars Liebert, Holberg & Bergeron 2005 Kepler et al. 2008 There are too many massive stars in both independent samples, fitting independent model grids to the spectra.

5. DAs and DBs in SDSS Same increase in mass happens for the DBs. The temperature in both cases is close to the when H and He become neutral. Solutions: improve the physics of the models (Tremblay & Bergeron 2011, Koester) observations in Sandia Labs of macroscopic samples hydrogen plasma samples that have the same conditions as white dwarf atmospheres (Falcon, Winget, Gomez, ...)

6. Photometric data Fitting the photometric data alone, we do not see any increase of mass for low temperatures.

7. A closer look… …magnetic fields Eye inspection indicated more structures than simply H lines. High mass models are preferred to fit the observations. The models do not really fit. (Kulebi et al. 2009)

8. Low S/N spectra We only re-observe a few stars (less than 10) with Gemini. Note that Gemini efficiency is optical for lower wavelengths.

9. Yet massive DA white dwarf stars (Kepler et al. 2006)

10. BPM 37093: “super diamond” Low amplitude pulsations and modes close frequency confirm the high mass nature of BPM 37093. (Kanaan et al. 2005, Metcalfe et al. 2004)

11. Looking for massive pulsators 4.1m SOAR Telescope (SOI) 2.1m Otto Struve Telescope (Argos)

12. Newest DA instability strip Lower mass: 0.8 M DA instability strip: blue triangles are the new massive pulsators.

13. GD 518: the most massive pulsating WD

14. Seismology of individual WD stars • Detect pulsation modes • DAVs: few modes (1 - 8 modes) • Theory of information: few free parameters • Massive WDs: core composition and crystalized portion

15. Seismology vs. Spectroscopy WDEC model grid: 10,600 < Teff< 12,300 0.5 < M< 1.1 10-9.5 < MH < 10-4 10-3.5 < Mhe<10-2 Method: grid search

16. Main period vs. Temperature Ensemble indicates two separate families, based on the main observed period.

17. Main pulsation period Old idea of “mode selection” discussed in Winget, van Horn & Hansen 1981

18. To complete the puzzle… Higher S/N spectra of massive white dwarfs Measure magnetic fields (spectropolarimetry) Longer observing runs to study massive pulsators Improve the models Muitoobrigada!