Presentation on theme: "Barbara G. Castanheira S. O. Kepler, D. Winget, J.J. Hermes, K. Bell, … University of Texas at Austin McDonald Observatory."— Presentation transcript:
Barbara G. Castanheira S. O. Kepler, D. Winget, J.J. Hermes, K. Bell, … University of Texas at Austin McDonald Observatory
White Dwarfs in the SDSS Apache Point Obs. 2.5 m telescope 640 fibers per plates – Å Resolution: S/N ~ 4 (g=20.2) Photometry: 5 bands Spectroscopy: candidates
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 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… 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) …magnetic fields
Models for magnetic field (Wickramasinghe & Ferrario 2000)
Double-degenerate scenario (Kawka, Vennes & Vaccaro 2010) Splitting of the H lines could be indicative of double- degenerate pair, instead of magnetic field.
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 (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 Lower mass: 0.8 M DA instability strip: blue triangles are the new massive pulsators.
GD 518: the most massive pulsating WD
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
Seismology vs. Spectroscopy WDEC model grid: 10,600 < T eff < 12, < M < < M H < < M he <10 -2 Method: grid search
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
Amplitude vs. Main Period Larger scatter for longer periods indicate they have higher amplitudes, as we do not know the inclination angle of the pulsation axis. Low amplitude for longest period is consistent with the theory that cooler stars have a deeper convection zone.
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!