Barbara G. Castanheira S. O. Kepler, D. Winget, J.J. Hermes, K. Bell, … University of Texas at Austin McDonald Observatory DQV 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 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. 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: 1. improve the physics of the models (Tremblay & Bergeron 2011, Koester) 2. observations in Sandia Labs of macroscopic samples hydrogen plasma samples that have the same conditions as white dwarf atmospheres (Falcon,Winget, Gomez, ...) Photometric data Fitting the photometric data alone, we do not see any increase of mass for low temperatures. A closer look… inspection indicated …magnetic fields Eye 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) 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. Yet massive DA white dwarf stars (Kepler et al. 2006) 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) Looking for massive pulsators 4.1m SOAR Telescope (SOI) 2.1m Otto Struve Telescope (Argos) Newest DA instability strip 1.20 Lower mass: 0.8 M DA instability strip: blue triangles are the new massive pulsators. 1.00 0.80 0.60 0.40 0.20 13000 12000 11000 Effective temperature (K) 10000 9000 GD 518: the most massive pulsating WD Seismology of individual WD stars - Detect pulsation modes M=1.05M_sun M_H=-6 M_He=-2 36.0 - DAVs: few modes (1 - 8 modes) - Theory of information: few free parameters - Massive WDs: core composition 34.0 and crystalized portion 32.0 30.0 12000 11800 Temperature (K) 11600 11400 Seismology vs. Spectroscopy 12500 12000 WDEC model grid: 11500 10,600 < Teff < 12,300 0.5 < M < 1.1 11000 10-9.5 < MH < 10-4 10500 10500 11000 11500 12000 10-3.5 < Mhe<10-2 12500 Method: grid search 1 0.95 0.9 0.85 0.8 0.75 0.75 0.8 0.85 0.9 0.95 1 Main period vs. Temperature Ensemble indicates two separate families, based on the main observed period. Main pulsation period Old idea of “mode selection” discussed in Winget, van Horn & Hansen 1981 To complete the puzzle… 1. Higher S/N spectra of massive white dwarfs 2. Measure magnetic fields (spectropolarimetry) 3. Longer observing runs to study massive pulsators 4. Improve the models Muito obrigada!