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

Edward M. Sion, Patrick Godon, Janine MyszkaEdward M. Sion, Patrick Godon, Janine MyszkaDepartment of Astronomy and Astrophysics Department of Astronomy and Astrophysics

Villanova UniversityVillanova University

Outline of Talk

1. CV White Dwarf Overview

2. The White Dwarf in the SS Cygni

3. Comments on Accretion Heating of CV White Dwarfs

4. The Big Picture of CV White Dwarf Surface Temperatures

5. Conclusion

White Dwarfs undergoing extreme accretion

Debris Disk accretion: ~ 10^8 g/s

Cataclysmic Disk accretion: ~ 10^18 g/s

CATACLYSMIC VARIABLE WHITE DWARFS: Extreme Accretion Laboratories

Figure 6

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

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

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

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

Far Ultraviolet SpectraFar Ultraviolet Spectra

IUE ArchivalIUE Archival

HST FOS, GHRS, STIS, COSHST FOS, GHRS, STIS, COS

FUSEFUSE

EUVEEUVE

Synthetic Spectra Synthetic Spectra

High Gravity LTE and NLTE Model High Gravity LTE and NLTE Model Atmospheres (TLUSTY200, SYNSPEC98)Atmospheres (TLUSTY200, SYNSPEC98)

Optically Thick, Steady State, Accretion Optically Thick, Steady State, Accretion Disk Models (TLUSDISK200)Disk Models (TLUSDISK200)

Accretion Belt ModelsAccretion Belt Models

Accretion RingsAccretion Rings

Accretion Curtain ModelsAccretion Curtain Models

Evolutionary Model SimulationsEvolutionary Model Simulationsof Accretionof Accretion

1D Quasi-Static Evolutionary Code, 1D Quasi-Static Evolutionary Code,

2D Hydrodynamic Code2D Hydrodynamic Code

OPAL OpacitiesOPAL Opacities

Time-variable accretion with compressional Time-variable accretion with compressional heating and boundary layer irradiation with heating and boundary layer irradiation with stellar rotation (Sion, E.1995, ApJ,438,876)stellar rotation (Sion, E.1995, ApJ,438,876)

Equations of State (ideal gas to relativistic Equations of State (ideal gas to relativistic degeneracy) degeneracy)

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

Best optically thick accretion disk modelE(B-V) = 0.04

Best optically thick accretion disk model

E(B-V) = 0.07

Best white dwarf photosphere model

Teff = 47000K, Log g =8.3, Vsini =200 km/s

Best WD + Disk Combination Fit

• -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)

Cooling Curve WZ Sge

Cooling Curve WZ SgeWD mass from Steeghs et al.2007,ApJ, 667, 442

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

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

Summary

1. 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.

3. 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.

4. 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.