Structured outflow from a Structured outflow from a dynamo-active accretion discdynamo-active accretion disc
B. von Rekowski, A. Brandenburg,
W. Dobler, A. Shukurov
A&A 398, 825-844
Bridging the gapsBridging the gaps
Dynamo theory
Disc theory
Jet theory(Ferreira)
(Küker)
(Hawley)
Model of disc dynamo,with feedback from disc,and allowing for outflows
Do jets require external fields?Do we get dipolar fields?Are they necessary?
Our inspirationOur inspiration
• Disc modeled as b.c.
• Adiabatic EOS– Virial temperature
• Need a cool disc
• Kepler rot. only for
Ouyed & Pudritz (1997)r
GMT
R
0T
Modeling a cool discModeling a cool disc
• vertical pressure eq.
• low T high density
• Entropy lower in disc– bi-polytropic model
Vertical cross-sectionthrough the disc
z
sTh
z
0
s
Thu2
Dynamo inputDynamo input
• Local disc simulations: cyclic fields– Quadrupolar for vacuum condition– Steady dipolar field for perfect conductor b.c.
• Dynamo alpha negative– Local mean-field models: similar results
• Global mean field models: always dipolar– Bardou et al. (2001), Campbell (2001)
Structured outflowStructured outflow
Disc temperature relative to halo is free parameter:Here about 3000K
Cooler disc: more vigorous evolution
Acceleration mechanismAcceleration mechanismDisc temperatureabout 3000 K
Ratio of magneto-centrifugal forceto pressure force
Unsteady Unsteady outflow is outflow is the rulethe rule
Momentum transport from the disc into the wind
Lagrangian Lagrangian invariantsinvariants
ii Buak /)(
/)(~ 1 Bua
kBual /)(
kBhae /~
)( 221 u
Comparison with Ouyed & Pudritz (1997)Comparison with Ouyed & Pudritz (1997)
Very similar:
Alfven Mach >1
Toroidal/poloidal field ratio increases
No asymptotic collimationNo asymptotic collimation
Conical outflows similar to BN/KLConical outflows similar to BN/KL
Greenhill et al (1998)
Application: magnetic Application: magnetic contamination of galaxy clustercontamination of galaxy cluster
10,000 galaxies for 1 Gyr, 1044 erg/s each
G182
tV
cMN
F
FB sw
kin
poyntrms
Similar figure also for outflows from protostellar disc
Further experiments: interaction with magnetosphereFurther experiments: interaction with magnetosphereAlternating fieldline uploading and downloadingAlternating fieldline uploading and downloading
Star connected with the disc Star disconnected from disc
Simil ar beh avior fo und b y G
oo dso n & W
ingl ee (19 99)
ConclusionsConclusions
• Conical outflow
• Collimation requires external field– cf talk by Menard (yesterday)
• Dipolar field comes automatically