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The White Dwarf in SS Cygni: FUSE + HST Spectral Analysis

The White Dwarf in SS Cygni: FUSE + HST Spectral Analysis. Edward M. Sion, Patrick Godon, Janine Myszka Department of Astronomy and Astrophysics Villanova University. Outline of Talk CV White Dwarf Overview 2. The White Dwarf in the SS Cygni 3. Comments on Accretion Heating

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The White Dwarf in SS Cygni: FUSE + HST Spectral Analysis

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  1. The White Dwarf in SS Cygni: FUSE + HST Spectral Analysis Edward M. Sion, Patrick Godon, Janine Myszka Department of Astronomy and Astrophysics Villanova University

  2. Outline of Talk • CV White Dwarf Overview • 2. The White Dwarf in the SS Cygni • 3. Comments on Accretion Heating • of CV White Dwarfs • The Big Picture of CV White Dwarf • Surface Temperatures • 5. Conclusion

  3. CATACLYSMIC VARIABLE WHITE DWARFS: Extreme Accretion Laboratories White Dwarfs undergoing extreme accretion Debris Disk accretion: ~ 10^8 g/s Cataclysmic Disk accretion: ~ 10^18 g/s

  4. Sion, E. M. et al. (2008), ApJ, 681, 543 Figure 6

  5. Godon, P. et al. (2008), ApJ, in press SS Aur SS Aur

  6. Brief Summary of CV WD Properties • CV white dwarfs have temperatures 8000K < Teff < 70,000K • CV white dwarfs have rotation velocities 100 < Vsini < 1200 km/s • CV white dwarf metal abundances tend to be subsolar. Several have N/C ~ 5 to 10 suprasolar P, Al • <Teff> = 15,000K below gap, <Teff> = 35,000K above gap

  7. OPEN QUESTIONS • Do CVs really evolve across the period gap? • Do CV white dwarf masses increase, stay the same, or decrease with time? • Are AM CVn helium transfer binaries Type Ia SN progenitors? • What is the evolutionary status of the Nova-like Variables? • Do we really understand accretion • disk structure? • Critical need for masses and parallaxes

  8. Far Ultraviolet Spectra • IUE Archival • HST FOS, GHRS, STIS, COS • FUSE • EUVE

  9. Synthetic Spectra • High Gravity LTE and NLTE Model Atmospheres (TLUSTY200, SYNSPEC98) • Optically Thick, Steady State, Accretion Disk Models (TLUSDISK200) • Accretion Belt Models • Accretion Rings • Accretion Curtain Models

  10. Evolutionary Model Simulationsof Accretion • 1D Quasi-Static Evolutionary Code, • 2D Hydrodynamic Code • OPAL Opacities • Time-variable accretion with compressional heating and boundary layer irradiation with stellar rotation (Sion, E.1995, ApJ,438,876) • Equations of State (ideal gas to relativistic degeneracy)

  11. SS Cygni The Brightest Dwarf Nova One of the first CVs Shown to be a Binary White Dwarf + K4-5V Roche-lobe filling companion P_orb = 0.27513 days (6.6 hours) Distance = 166 pc +/- 12pc(Trig.parallax; Harrison et al.1999) (but see Schreiber&Lasota,2007,A\&A,473,897; Schreiber&Gaensicke,2002,A\&A,382,124) <t_rec> = 50 days <t_ob> = 10.76 days <t_quies> = 37.81 days

  12. Best optically thick accretion disk model E(B-V) = 0.04

  13. Best optically thick accretion disk model E(B-V) = 0.07

  14. Best white dwarf photosphere model Teff = 47000K, Log g =8.3, Vsini =200 km/s

  15. Best WD + Disk Combination Fit

  16. -8.0 & 41 & --- & 1.331 & 862 & --- & 100 & 0.04 -8.0 & 60 & --- & 1.227 & 629 & --- & 100 & 0.04 -9.0 & 41 & --- & 1.989 & 308 & --- & 100 & 0.04 -9.0 & 60 & --- & 2.690 & 216 & --- & 100 & 0.04 -9.5 & 41 & --- & 6.477 & 157 & --- & 100 & 0.04 -9.5 & 50 & --- & 8.036 & 142 & --- & 100 & 0.04 -9.5 & 60 & --- & 9.122 & 106 & --- & 100 & 0.04 -8.0 & 41 & --- & 1.615 & 741 & --- & 100 & 0.07 -8.0 & 60 & --- & 1.810 & 541 & --- & 100 & 0.07 -9.0 & 41 & --- & 3.562 & 265 & --- & 100 & 0.07 -9.0 & 60 & --- & 4.754 & 186 & --- & 100 & 0.07 --- & --- & 40000 & 1.637 & 138 & 100& --- & 0.04 --- & --- & 47000 & 1.990 & 167 & 100& --- & 0.04 --- & --- & 46000 & 1.451 & 139 & 100& --- & 0.07 --- & --- & 55000 & 1.600 & 164 & 100& --- & 0.07 -10.5 & 50 & 41000 & 1.490 & 143 & 98& 2 & 0.04 -10 & 50 & 46,000 & 1.258 & 173 & 88& 12 & 0.04 -9.5 & 50 & 55,000 & 1.255 & 233 & 66& 34 & 0.04 -10.5 & 50 & 49,000 & 1.429 & 149 & 98& 2 & 0.07 -10 & 50 & 55,000 & 1.385 & 172 & 91& 9 & 0.07 -9.5 & 50 & 70,000 & 1.630 & 222 & 72& 28 & 0.07 M i T_wd Chi^2 d %WD %disk E(B-V)

  17. Cooling Curve WZ Sge

  18. Cooling Curve WZ Sge WD mass from Steeghs et al. 2007,ApJ, 667, 442

  19. Temperatures from Long,K.et al. 2009, ApJ, 697, 1512

  20. Temperatures from Long, K. et al.2009, ApJ, 697, 1512

  21. Summary • The white dwarf in SS Cygni dominates the quiescent FUV • flux from the Lyman Limit to 2000A. • 2. With M_wd = 0.81 Msun(Bitner, Robinson & Behr 2007, • ApJ, 662, 564) the WD surface temperature is • in the range of 46000K < T_eff < 55000K • depending upon whether E(B-V) =0.04 or 0.07. • Compressional heating ALONE may not explain • the cooling of the superoutburst accretion-heated • white dwarfs in two of the best studied dwarf novae, • WZ Sge and VW Hydri. • The very broad distribution of CV white dwarf • temperatures, versus <Mdot>, above the period • gap poses a severe challenge to our understanding • of CV evolution.

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