shaping the outbursts of dwarf novae with matthew s. b...
TRANSCRIPT
Generating Lightcurves
500 520 540 560 580 600
Time (days)
8
9
10
11
12
13
14
MV
DIMRItr-1.5e16, Mtr = 1.5×1016
OverviewDwarf Novae:• Accreting white
dwarfs in binaries• Outbursts typically
last a few days andhave recurrence timeseveral weeks
• Outbursts triggered byhydrogen ionizationinstability in theaccretion disk
Abridged ReferenceBalbus, S. A., & Hawley, J. F. 1991, ApJ, 376, 214Bodo, G., Cattaneo, F., Mignone, A., & Rossi, P. 2012, ApJ, 761, 116Kotko, I., & Lasota, J.P. 2012, A&A, 545, A115Kotko I., Lasota J.P., Dubus G., Hameury J.M., 2012, A&A, 544, A13Lasota J.P., 2001, NewAR, 45, 449Shakura, N. I., & Sunyaev, R. A. 1973, A&A, 24, 337Wheatley, P. J., Mauche, C. W., & Mattei, J. A. 2003, MNRAS, 345, 49
AcknowledgementsThis research was supported by the United States NSF grant AST1412417.We also acknowledge support from the UCSB Academic Senate, and theCenter for Scientific Computing from the CNSI, MRL: an NSF MRSEC(DMR1121053) and NSF CNS0960316. Numerical calculation was partlycarried out on the Cray XC30 at CfCA, National Astronomical Observatoryof Japan, and on SR16000 at YITP in Kyoto University.
Shaping the Outbursts of Dwarf Novae withConvection and Magnetorotational Turbulence
Matthew S. B. [email protected] of Physics
University of California, Santa Barbara
Convection Modifies MagnetorotationalTurbulence and Dynamos
SS Cygni Lightcurve
100 200 300 400 500 600 700 800 900
8
10
12
Date [JD‑2450000]
Vis
ual
Mag
nitu
de
Fig 2: Visual lightcurve of the dwarf nova SS Cygni from Wheatley et al., 2003.
Motivation:• Properties of steady state disks are insensitive to the stress
to pressure ratio/viscosity parameter α• The mechanisms which determine α are not well
understood• Time variations of dwarf nova outbursts probe α
The relative durations of quiescence and outburstimplies that α is larger in outburst
• Values of α measured from magnetohydrodynamic(MHD) simulations tend to be inconsistent with the valuesinferred from observations
Methods:• 3D radiationMHD local disk simulations using Zeus
Realistic opacities and equation of state• Modified disk instability model incorporating simulation
results
WhiteDwarf
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0.02
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Log effective temperature (K)
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Log effective temperature (K)
0.02
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3.0 3.2 3.4 3.6 3.8 4.0
Log effective temperature (K)
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Log effective temperature (K)
0.02
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A
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Log effective temperature (K)
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Log effective temperature (K)
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Surface density (g cm )−2
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Log effective temperature (K)
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Con
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100 1000Surface density (g cm−2)
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Log effective temperature (K)
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Con
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100 1000Surface density (g cm−2)
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Log effective temperature (K)
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Con
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0.5
0.6
0.7
0.8
Bz2 /Bx
2
vz2 /vx
2
C
100 1000Surface density (g cm−2)
10−1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz2 / Σ4/3
D
3.0 3.2 3.4 3.6 3.8 4.0
Log effective temperature (K)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Con
vect
ive
frac
tion
B
0.4
0.5
0.6
0.7
0.8
Bz2 /Bx
2
vz2 /vx
2
C
100 1000Surface density (g cm−2)
10−1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz2 / Σ4/3
D
3.0 3.2 3.4 3.6 3.8 4.0
Log effective temperature (K)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Con
vect
ive
frac
tion
B
0.4
0.5
0.6
0.7
0.8
Bz2 /Bx
2
vz2 /vx
2
C
100 1000Surface density (g cm−2)
10−1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz2 / Σ4/3
D
3.0 3.2 3.4 3.6 3.8 4.0
Log effective temperature (K)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Con
vect
ive
frac
tion
B
0.4
0.5
0.6
0.7
0.8
Bz2 /Bx
2
vz2 /vx
2
C
100 1000Surface density (g cm−2)
10−1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz2 / Σ4/3
D
3.0 3.2 3.4 3.6 3.8 4.0
Log effective temperature (K)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Con
vect
ive
frac
tion
B
0.4
0.5
0.6
0.7
0.8
Bz2 /Bx
2
vz2 /vx
2
C
100 1000Surface density (g cm−2)
10−1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz2 / Σ4/3
D
3.0 3.2 3.4 3.6 3.8 4.0
Log effective temperature (K)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Con
vect
ive
frac
tion
B
0.4
0.5
0.6
0.7
0.8
Bz2 /Bx
2
vz2 /vx
2
C
100 1000Surface density (g cm−2)
10−1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz2 / Σ4/3
D
3.0 3.2 3.4 3.6 3.8 4.0
Log effective temperature (K)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Con
vect
ive
frac
tion
B
0.4
0.5
0.6
0.7
0.8
Bz2 /Bx
2
vz2 /vx
2
C
100 1000Surface density (g cm−2)
10−1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz2 / Σ4/3
D
3.0 3.2 3.4 3.6 3.8 4.0
Log effective temperature (K)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Con
vect
ive
frac
tion
B
0.4
0.5
0.6
0.7
0.8
Bz2 /Bx
2
vz2 /vx
2
C
100 1000Surface density (g cm−2)
10−1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz2 / Σ4/3
D
3.0 3.2 3.4 3.6 3.8 4.0
Log effective temperature (K)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Con
vect
ive
frac
tion
B
0.4
0.5
0.6
0.7
0.8
Bz2 /Bx
2
vz2 /vx
2
C
100 1000Surface density (g cm−2)
10−1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz2 / Σ4/3
D
3.0 3.2 3.4 3.6 3.8 4.0
Log effective temperature (K)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Con
vect
ive
frac
tion
B
0.4
0.5
0.6
0.7
0.8
Bz2 /Bx
2
vz2 /vx
2
C
100 1000Surface density (g cm−2)
10−1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz2 / Σ4/3
D
3.0 3.2 3.4 3.6 3.8 4.0
Log effective temperature (K)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Con
vect
ive
frac
tion
B
0.4
0.5
0.6
0.7
0.8
Bz2 /Bx
2
vz2 /vx
2
C
100 1000Surface density (g cm−2)
10−1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz2 / Σ4/3
D
3.0 3.2 3.4 3.6 3.8 4.0
Log effective temperature (K)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Con
vect
ive
frac
tion
B
0.4
0.5
0.6
0.7
0.8
Bz2 /Bx
2
vz2 /vx
2
C
100 1000Surface density (g cm−2)
10−1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz2 / Σ4/3
D
3.0 3.2 3.4 3.6 3.8 4.0
Log effective temperature (K)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Con
vect
ive
frac
tion
B
0.4
0.5
0.6
0.7
0.8
Bz2 /Bx
2
vz2 /vx
2
C
100 1000Surface density (g cm−2)
10−1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz2 / Σ4/3
D
3.0 3.2 3.4 3.6 3.8 4.0
Log effective temperature (K)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Con
vect
ive
frac
tion
B
0.4
0.5
0.6
0.7
0.8
Bz2 /Bx
2
vz2 /vx
2
C
100 1000Surface density (g cm−2)
10−1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz2 / Σ4/3
D
3.0 3.2 3.4 3.6 3.8 4.0
Log effective temperature (K)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Con
vect
ive
frac
tion
B
0.4
0.5
0.6
0.7
0.8
Bz2 /Bx
2
vz2 /vx
2
C
100 1000Surface density (g cm−2)
10−1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz2 / Σ4/3
D
3.0 3.2 3.4 3.6 3.8 4.0
Log effective temperature (K)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Con
vect
ive
frac
tion
B
0.4
0.5
0.6
0.7
0.8
Bz2 /Bx
2
vz2 /vx
2
C
100 1000Surface density (g cm−2)
10−1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz2 / Σ4/3
D
3.0 3.2 3.4 3.6 3.8 4.0
Log effective temperature (K)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
α
A
0.0
0.2
0.4
0.6
Convective fraction
B
0.4
0.5
0.6
0.7
0.8
Bz 2 /B
x 2
vz 2 /v
x 2
C
1001000
Surface density (g cm
−2)
10−
1
100
101
102
103
pressure / Σ4/3
stress / Σ4/3
Bz 2 / Σ
4/3
D
3.03.2
3.43.6
3.84.0
Log effective temperature (K
)
100 1000
Surface density (g cm )−2
ws0446
ws0429
ws0446
ws0429
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Time (Orbits)
−2
−1
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2
Hei
ght
/1.
41×1
09cm
ws0429
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Time (Orbits)
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−1
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2
Hei
ght
/9.
51×1
08cm
ws0446
fconv
−2.0
−1.5
−1.0
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2.0
By
×103
−800
−600
−400
−200
0
200
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By
−0.3 −0.2 −0.1 0.0 0.1 0.2
δs/ 〈s〉
−0.5
0.0
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By
×103 Above Midplane
−0.3 −0.2 −0.1 0.0 0.1 0.2
δs/ 〈s〉
−0.5
0.0
0.5
1.0×103 Below Midplane
10−4
10−3
10−2
ws0446
Fig 1: Dwarf nova schematic. The jet emanatingfrom the white dwarf is only observable in radio.
102 103
Σ(g/cm2)
103
104
Teff
(K)
Σ+crit, T
+eff,crit
Σ−crit, T−eff,crit
DIM
DIMa
DIMRI
MRI Sims
5 10 15
100× α
Upper Branch
Lower Branch
Fig 3: We use the local shearing box approximation in our MHD simulations.
Convection Enhances α
By including realistic opacities and equation of state appropriate for the hydrogen ionization regime,we found that convection occurs in the low temperature region of the outburst state (the upper branchof the scurve). This convection enhances the magnetorotational turbulence and α, resulting in valuesof α which are consistent with those recovered from observations.
Fig 4: Timeaveraged stress to pressure ratio α (A) and convective fraction (B) as a function of surface mass density. Eachpoint represents the time averaged quantities from one shearing box simulation. Colors represent the timeaveragedeffective temperature of each simulation. The convective fraction is the pressure weighted fraction of energy transport doneby the advection of gas internal energy. The simulations ws0429 and ws0446 have been labeled as they are examined inmore detail below.
Fig 6: 2D histograms of azimuthal magnetic field (By, vertical axis) and deviations from the horizontal average of specificentropy (δs, horizontal axis). Each cell saved to file from ws0446 with 80≤t≤100 and 0≤z≤0.25 simulation units (left) and0.25≤z≤0 simulation units (right) are used to create the respective histograms. It is important to note that for both panelsthere is a low entropy, high |By| tail which corresponds to the sign of the respective wings of the butterfly diagram (seebottom panel of Fig. 5), indicating that convection is mixing regions of high magnetization from the wings into themidplane.
Fig 5: Horizontallyaveraged (averaged in x and y) azimuthal magnetic field (By) as a function of time and height for aradiative simulation (ws0429, left) and a simulation which exhibits convective epochs (ws0446, right). The dashed blacklines show the timedependent heights of the photospheres in the horizontally averaged structures. For simulation ws0446,which exhibits convection, the convective fraction fconv‑2 is plotted in magenta, and uses the same vertical scale as By, i.e.when the magenta line is near 1 then fconv ≈ 1.
Fig 7: Left: Loci of thermal equilibria in the effective temperature Teff vs. surface mass density Σ plane (the “Scurve”) atradius R=1.25×1010 cm for the standard DIM, DIMa and DIMRI. The MRI simulation results are gray crosses (one pointfor each stable simulation). Additionally, the ends of the upper (Σ+
crit, T+eff,crit) and lower (Σ
crit, Teff,crit) branches are
marked for DIM. Right: The MRIbased α(Teff) fit to simulation plotted sideways in solid black (DIMa and DIMRI bothuse this fit) with the results from the same MRI simulations from the left plotted as gray crosses. The variation of α used byDIM is plotted as the dotted black line.
Fig 8: Light curves calculated from DIMRI with inner disc radius truncated by the magnetic field with magnetic momentμ=8×1030 G cm3 and Mtr=1.5×1016 g s1.
.
My Related Publications:Convective Quenching of Field Reversals in Accretion Disc Dynamos
Coleman, M. S. B., Yerger, E., Blaes, O., Salvesen, G., & Hirose, S., 2017, MNRAS, SubmittedDwarf nova outbursts with magnetorotational turbulence
Coleman, M. S. B., Kotko, I., Blaes, O., Lasota, J.P., & Hirose, S., 2016, MNRAS, 462, 3710Convection Causes Enhanced Magnetic Turbulence in Accretion Disks in Outburst
Hirose, S., Blaes, O., Krolik, J. H., Coleman, M. S. B., & Sano, T., 2014, ApJ, 787, 1
My publicationsand posters
Convection Quenches Magnetic Field Reversals
We noticed that the dynamo behavior of our simulations is very different when convection is present(see Fig. 5). Typically, MHD shearing box simulations with low magnetization exhibit a socalledbutterfly diagram of quasiperiodic azimuthal magnetic field (By) reversals. For our simulations whichexhibit convection, the convection is intermittent and so are the disturbances of the dynamo. Duringconvective epochs the azimuthal field no longer reverses.0 50 100 150
Time (Orbits)
−2
−1
0
1
2
Hei
ght
/1.
41×1
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ws0429
0 20 40 60 80 100 120 140 160
Time (Orbits)
−2
−1
0
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2
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ght
/9.
51×1
08cm
ws0446
fconv
−2.0
−1.5
−1.0
−0.5
0.0
0.5
1.0
1.5
2.0
By
×103
−800
−600
−400
−200
0
200
400
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800
By
The primary role of convection in disrupting the butterfly diagram, is to mix magnetic field from highaltitude down into the midplane. This mixing was identified through correlations between entropy andBy (see Fig. 6). Due to the high opacity of the convective epochs, perturbed fluid parcels maintaintheir entropy for many dynamical times. Hence the observed lowentropy highlymagnetized fluidparcels found in the midplane must have been mixed in from the wings.
The Disk Instability Model (DIM) has been successful in reproducing the observed light curves ofdwarf nova outbursts by invoking an adhoc enhanced α parameter ~0.10.2 in outburst compared to alow value ~0.01 in quiescence. The convective enhancement of α in outburst we found only acts nearthe hydrogen ionization transition. To check if this enhancement is sufficient to reproduce observedlight curves, we incorporate this MRIbased variation in α into the DIM, as well as modifications tothe vertical structure, using simulationbased models of turbulent dissipation and convective transport.
The Equilibrium Scurve
The DIM uses a library of equilibrium vertical structures to determine how adjacent annuli in theaccretion disk communicate. The equilibrium structures for a single annulus are typically plotted in thesurface mass density, effective temperature plane, resulting in the standard Scurve. The mass transferrate from the secondary tries to drive the accretion disk to the middle unstable branch, however due toits unstable nature, the disk instead switches between quiescence (lower branch) and outburst (upperbranch). The edges of the branches of the scurve and the value of α, shape the outburst lightcurve.
Classic DIM
DIM with α(Teff)
DIM with α(Teff) andvertical structure
modifications