influence of h2 formation on pdr model results
DESCRIPTION
Influence of H2 formation on PDR model results. M. Röllig V. Ossenkopf, C. Glück Universität zu Köln, Germany . Outline. H 2 formation on grain surfaces chemisorption vs. physisorption H 2 formation efficiencies on different dust sorts chemical H 2 heating & cooling - PowerPoint PPT PresentationTRANSCRIPT
CO Ladder Workshop - Leiden 2012
Influence of H2 formation on PDR model results
M. Röllig V. Ossenkopf, C. Glück
Universität zu Köln, Germany
CO Ladder Workshop - Leiden 2012
Outline
• H2 formation on grain surfaces– chemisorption vs. physisorption– H2 formation efficiencies on different dust sorts– chemical H2 heating & cooling– effects on clump structure
CO Ladder Workshop - Leiden 2012
IntroductionNumerical PDR models of proved to be a valuable tools in analyzing and understanding the local conditions in massive star forming regions.
Ossenkopf et al, 2010, A&A 518, L79v
Hollenbach & Tielens, 1999, R.o.m.P., 71
CO Ladder Workshop - Leiden 2012
Introduction
Yet, here be dragons...• complex physics /
chemistry
• complex/unknown local conditions
Röllig et al. 2007, A&A, 467
θ1Ori C (O6)
CO Ladder Workshop - Leiden 2012
Introduction
and unfortunately, deficient input data
• missing experimental data
• inter/extrapolation
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H2 formation on grain surfaces
CO Ladder Workshop - Leiden 2012
H2 formation on grain surfaces
• H atoms hitting grain surfaces can stick weakly (physisorption) or strongly (chemisorption) bound.
• Td>100 K desorption overcomes binding and H2 formation efficiency →0
• Chemisorbed H atoms can effectively form H2 up to Td>500K
• we implemented the formalism presented by Cazaux & Tielens (2002,2004) in the KOSMA- chemistry.
CO Ladder Workshop - Leiden 2012
H2 formation efficiency
Cazaux & Tielens 2004, ApJ 604
CO Ladder Workshop - Leiden 2012
H2 formation efficiency
Cazaux & Tielens 2004, ApJ 604
CO Ladder Workshop - Leiden 2012
H2 formation efficiency
Cazaux & Tielens 2004, ApJ 604
CO Ladder Workshop - Leiden 2012
H2 formation efficiency
Cazaux & Tielens 2004, ApJ 604
CO Ladder Workshop - Leiden 2012
H2 formation ratetotal formation ratedepends on total dustsurface
CO Ladder Workshop - Leiden 2012
H2 formation rate
Weingartner and Draine, 2001, ApJ 548
CO Ladder Workshop - Leiden 2012
H2 formation rate
100 101 102 103
10 18
10 17
10 16
T d K
R ds1 W D 0107
W D 0121
W D 0125
w ith P A H s
no P A H s
T g 50 K
CO Ladder Workshop - Leiden 2012
H2 heating/cooling
• H2 binding energy 4.5 eV → H2 formation heating
• kinetic H2 dissociation cooling (Lepp & Shull, 1983, ApJ 270, 578)
H2 + H → H + H + H - 4.5eVH2 + H2 → H2 + H + H - 4.5eV
Alternatively: sticking coeff.
CO Ladder Workshop - Leiden 2012
H2 heating/cooling
Le Bourlot et al. 2012
CO Ladder Workshop - Leiden 2012
H2 heating/cooling
Le Bourlot et al. 2012
CO Ladder Workshop - Leiden 2012
H2 heating/cooling
Le Bourlot et al. 2012A: R=const, B: only LH, C=LH+ER
CO Ladder Workshop - Leiden 2012
H2 heating/cooling
Le Bourlot et al. 2012A: R=const, B: only LH, C=LH+ER
CO Ladder Workshop - Leiden 2012
Dust influence
CO Ladder Workshop - Leiden 2012
Dust influence
radiative transfer effect H2 chemistry effect
CO Ladder Workshop - Leiden 2012
Dust influence
• H2 binding energy 4.5 eV → H2 formation heating
• kinetic H2 dissociation cooling (Lepp & Shull, 1983, ApJ 270, 578)
H2 + H → H + H + H - 4.5eVH2 + H2 → H2 + H + H - 4.5eV
• large effect on H-H2 transition region chemistry
CO Ladder Workshop - Leiden 2012
Dust influence• H2 binding energy 4.5 eV
→ H2 formation heating
• kinetic H2 dissociation cooling (Lepp & Shull, 1983, ApJ 270, 578)
H2 + H → H + H + HH2 + H2 → H2 + H + H
• large effect on H-H2 transition region chemistry
• chemistry physics
CO Ladder Workshop - Leiden 2012
Summary
• Great need for reliable (astrochemistry) data• Lab results need to be robust against different
modeling applications• Growing understanding of dust properties and
H2 formation process dramatically influences model results
• chemistry and physics strongly connected to each other