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
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 ?
Morphology of magnetic fields
1.4 GHz Lang et al. 99
171 Angstrom TRACE strong field cases: longitudinal coherencestrong field cases: longitudinal coherence
Molecular Clouds
gravity thermal pressureturbulencemagnetic field
right:filaments in Orion850 emission polarized Johnstone & Bally 99
left: elephant trunks in Rosette NebulaHCarlqvist et al. 03
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
NGC 3132
87” x 61”
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”
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”
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”
NGC 6537H, [N II]
field 9” x 8”
filaments part of torus n~104 cm-3, P~3 10-8 dynes
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
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