Signatures of Magnetic Field Structure in Planetary Nebulae

1
Signatures of Magnetic Field Structure in
Planetary Nebulae
PNe as MHD systems

• P. J. Huggins, New York University

2
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
171 Angstrom TRACE
1.4 GHz Lang et al. 99
strong field cases longitudinal coherence
4

• Molecular Clouds
• gravity thermal pressureturbulencemagnetic
  field
• rightfilaments in Orion850 m emission
  polarized Johnstone Bally 99
• left elephant trunks in Rosette
  NebulaHaCarlqvist 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, Brn, n 1,2,3
  uncertain
• strategy
• search for connected structures
• examine what fields are needed to provide
  coherence
• we present 3 examples

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NGC 3132
87 x 61
7

• tangential, multi-stranded, looped
• width 4 1015 cm, l/w gt60
• proposal magnetic filaments
• n 105 cm-3, P 10-9 dyne cm-2

NGC 3132 O III N II
12 x 19
8

• tangential, l/wgt40, like spaghetti
• proposal magnetic filaments
• n4 104 cm-3, P10-7 dyne cm-2

IC 418 Ha un-sharp mask
18 x 18
9

• tangential, l/wgt40, like spaghetti
• proposal magnetic filaments
• n4 104 cm-3, P10-7 dyne cm-2

IC 418 N II, Ha un-sharp mask
18 x 18
10
NGC 6537 Ha, N II field 9 x 8

• filaments part of torus
• n104 cm-3, P3 10-8 dynes

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If filaments are magnetic are the fields strong
enough ?

• rough field estimates
• b 8p P/B2 1, pressure
• s B2/4prv2 1, n vexp
• compare with AGB fields
• our estimates are upper limits
• s 1/10 still robust
• likely compressionAGB 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 fields