Signatures of Magnetic Field Structure in Planetary Nebulae
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Signatures of Magnetic Field Structure in
Planetary Nebulae
Signatures of Magnetic Field Structure in
Planetary Nebulae
P. J. Huggins, New York University
PNe as MHD systemsPNe as MHD systems
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Can we see MHD in PNe ?
ample evidence for mag fields in PNe: jet origin – binary disks/single stars fields in AGB envelopes and proto/young-PNe surface fields CS PNe (Jordan et al. 05)
can we identify direct effects of MHD in PN images is the complex structure in PNe caused by MFs ? can structure be used to probe MF ?
we divide the question into 3 parts:
what to look for ? is there morphological evidence in PN images ? are the fields strong enough ?
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Morphology of magnetic fields
1.4 GHz Lang et al. 99
171 Angstrom TRACE strong field cases: longitudinal coherencestrong field cases: longitudinal coherence
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Molecular Clouds
gravity thermal pressureturbulencemagnetic field
right:filaments in Orion850 emission polarized Johnstone & Bally 99
left: elephant trunks in Rosette NebulaHCarlqvist et al. 03
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Looking for MHD in PNe morphological signature: connectedness – filaments
PNe are different from the molecular cloud case: turbulence weak, radial velocity helps preserve geometry source of magnetic fields: central star 10” at 500 pc ~ 1017 cm, B~rn, n= 1,2,3 – uncertain
strategy search for connected structures examine what fields are needed to provide coherence
we present 3 exampleswe present 3 examples
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NGC 3132
87” x 61”
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tangential, multi-stranded, looped width ~ 4 1015 cm, l/w >60 proposal: magnetic filaments n ~ 105 cm-3, P ~ 10-9 dyne cm-2
NGC 3132 [O III] [N II] 12” x 19”
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tangential, l/w>40, like spaghetti proposal: magnetic filaments n~4 104 cm-3, P~10-7 dyne cm-2
IC 418 H un-sharp mask 18” x 18”
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tangential, l/w>40, like spaghetti proposal: magnetic filaments n~4 104 cm-3, P~10-7 dyne cm-2
IC 418 [N II], H un-sharp mask 18” x 18”
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NGC 6537H, [N II]
field 9” x 8”
filaments part of torus n~104 cm-3, P~3 10-8 dynes
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If filaments are magnetic are the fields strong enough ?
rough field estimates: = 8 P/B2 ~ 1, pressure = B2/4v2 ~ 1, n vexp
compare with AGB fields our estimates are upper limits 1/10 still robust likely compression
AGB – PN transition
“magnetic filament” concept consistent with AGB fields
~ mG at 1017 cm
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Summary & Conclusions
Magnetic fields produce connected structures – filaments
PNe described here exhibit extreme filaments large length/width ratios & tangential, curved geometry field estimates consistent with fields in AGB envelopes
Proposal: filaments are signatures of magnetic field difficult to produce in any other way
Conclude: PN fields are localized and stringy Not convinced? Challenge: form similar filaments without fieldsNot convinced? Challenge: form similar filaments without fields