Injection of Small Bodies into the ISM by

Planetary Nebulae.

Bob O’Dell

University of Chicago

18 April 2007

NGC 6720-The Ring Nebula

IC 4406-The Retina Nebula

NGC 2392The Eskimo Nebula

NGC 6853 WFPC2

Final.Dec16XV.tif

Helix-Both FOV

Helix Close-up

Helix-Very Closeup

Helix CharacteristicsDistance=213 pc. Angular Size~10’Age ~15,000 years

Well imaged in optical lines (HST-ACS & CTIO-MOSAIC),

infrared (HST-NIC3-H2), and Radio (21-cm of HI, CO)

Ionization Structure

GO 9489 Slit

Slitless.fourlines

NewProfiles

HenneyConstTemp

HenneyVariableT

Predicting the Surface Brightness of the Knot Cusps.

• The most simplistic model argues that the surface brightness should drop with r-2, which meant this should be the upper limit to an observed SH~-2 relation.

ObservedSurface Brightness

Predicting the Surface Brightness of the Knot Cusps.

• The most simplistic model argues that the surface brightness should drop with r-2, which meant this should be the upper limit to an observed SH~-2 relation.

• Due to advection of neutral material into the ionized cusp, not all photons reach the ionization front of the cusps (Lopez-Martin et al. 2001, ApJ, 548, 288) so that the upper limit should be lower.

Predicted Surface Brightness

Knot Characteristics

• Total Number about 3,500-20,000.

• Mass from extinction~3x10-5 Suns.

• Total mass about 0.1-0.6 Suns.

• The central star mass is about 0.6 Suns.

• The original mass is about 3 Suns.

• A significant and possibly majority fraction of the mass is concentrated in knots.

Evolution of Knots• Initiated at the ionization front via an

instability (R-T, Capriotti 1973).

• Shaped by the radiation field of the star, starting out as broad and becoming comet-like in appearance.

Final Evolution ofa Central Star.

Shadows behind the Knots.• The first order theory has been worked out

already (Canto et al. 1998, ApJ, 502, 695.

• Since the knots are optically thick to LyC, they cast an ionization shadow.

• Some ionization occurs because of LyC photons scattered by the ambient nebula.

The Bulk of the Mass is in theNeutral Region of the Knots.

• Densities inferred from the optical are about 106 cm-3.

• Only one study of a heavy molecule (CO).

• H2 is expected to be the dominant form of hydrogen in the outer parts of the knots.

The Bulk of the Gas is in the Neutral Region and H2 is the strongest emission from there.

The H2 Levels

The NIC3 FOV inGO 10628

Northern FOV inMultiple Lines.

Profiles of 378-801 in the Emission Lines.

Mechanisms Proposed to Power the H2 Emission.

• Shocks driven by a high velocity wind from the central star.

Mechanisms Proposed to Power the H2 Emission.

• Shocks driven by a high velocity wind from the central star.

• Pumping by the FUV continuum followed by decay (the Solomon process).

The H2 Levels

Mechanisms Proposed to Power the H2 Emission.

• Shocks driven by a high velocity wind from the central star.

• Pumping by the FUV continuum followed by decay (the Solomon process).

• Photodissociation by x-rays followed by collisional heating of the gas.

Mechanisms Proposed to Power the H2 Emission.

• Shocks driven by a high velocity wind from the central star.

• Pumping by the FUV continuum followed by decay (the Solomon process).

• Photodissociation by x-rays followed by collisional heating of the gas.

• Photodissociation by EUV (the LyC) followed by collisional heating.

The Energy Balance.

• IN: X-ray(<124 A) 4x10-11 ergs cm-2 s-1

• IN: FUV (912-1200 A) 7x10-9 ergs cm-2 s-1

• IN: EUV (124-912 A) 8x10-8 ergs cm-2 s-1

• Out: Ionized Gas Lines 5x10-9 ergs cm-2 s-1

• Out:H2 Emission Lines 4x10-9 ergs cm-2 s-1

The Population Distribution.

The EUV Driven Model.

• This must have a density >105 cm-3.• It must have a collisionally heated gas of about

990 K.• It must have a zone where H2 still exists and yet

there are LyC photons .• The key physics is in advection, which was

necessary for explaining the surface brightness in Ha and the electron temperature increase in the ionized gas zone.

Evolution of Knots-I• Will they survive the expulsion phase?• Almost certainly they will survive the high

LyC luminosity phase of the central star since the photoevaporation time is about 15,000 years and it must decrease as the star gets fainter.

Evolution of Knots-II• The question then is whether they will survive

destruction by the diffuse UV radiation field of the ISM before being incorporated into GMC’s.

• There is ample and growing evidence for small scale structures in the ISM. This process could be the source.

Helix Reading• 3-D Model-O’Dell et al. 2004,AJ,128,2339&

RMxAAC, 23, 5.• 3-D Model-Meaburn et al. 1998,MNRAS,294,201&

2005,MNRAS,360,963.• Knot Ubiquity-O’Dell et al. 2002,AJ,123,3329.• Knot Basics-O’Dell & Burkert, 1997,IAU180, 332.• Detailed Knot Modeling-O’Dell, Henney, & Ferland

2005,AJ,130,172.• H2 Observations-Meixner et al. 2005,AJ,130,1784.

• H2 Energetics-O’Dell, Henney, & Ferland 2007, AJ, 133, 2343.