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
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
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
Sion, E. M. et al. (2008), ApJ, 681, 543
Figure 6
Godon, P. et al. (2008), ApJ, in press
SSSS
AurAur
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 Spectra
 IUE Archival
 HST FOS, GHRS, STIS, COS
 FUSE
 EUVE
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
Evolutionary Model Simulations
of 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)
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 model
E(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
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
M
-8.0
-8.0
-9.0
-9.0
-9.5
-9.5
-9.5
-8.0
-8.0
-9.0
-9.0
---------10.5
-10
-9.5
-10.5
-10
-9.5
i
& 41 &
& 60 &
& 41 &
& 60 &
& 41 &
& 50 &
& 60 &
& 41 &
& 60 &
& 41 &
& 60 &
& --- &
& --- &
& --- &
& --- &
& 50 &
& 50 &
& 50 &
& 50 &
& 50 &
& 50 &
T_wd
Chi^2
--- & 1.331 &
--- & 1.227 &
--- & 1.989 &
--- & 2.690 &
--- & 6.477 &
--- & 8.036 &
--- & 9.122 &
--- & 1.615 &
--- & 1.810 &
--- & 3.562 &
--& 4.754 &
40000 & 1.637 &
47000 & 1.990 &
46000 & 1.451 &
55000 & 1.600 &
41000 & 1.490 &
46,000 & 1.258 &
55,000 & 1.255 &
49,000 & 1.429 &
55,000 & 1.385 &
70,000 & 1.630 &
d
862
629
308
216
157
142
106
741
541
265
186
138
167
139
164
143
173
233
149
172
222
%WD %disk E(B-V)
&
&
&
&
&
&
&
&
&
&
&
&
&
&
&
&
&
&
&
&
&
--- &
--- &
--- &
--- &
--- &
--- &
--- &
--- &
--- &
--- &
--- &
100&
100&
100&
100&
98&
88&
66&
98&
91&
72&
100 & 0.04
100 & 0.04
100 & 0.04
100 & 0.04
100 & 0.04
100 & 0.04
100 & 0.04
100 & 0.07
100 & 0.07
100 & 0.07
100 & 0.07
--- & 0.04
--- & 0.04
--- & 0.07
--- & 0.07
2 & 0.04
12 & 0.04
34 & 0.04
2 & 0.07
9 & 0.07
28 & 0.07
Cooling Curve WZ Sge
WD mass from Steeghs et al.
2007,ApJ, 667, 442
Cooling Curve WZ Sge
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.