J/A+A/321/293 SiO production in interstellar shocks (Schilke+ 1997)
SiO production in interstellar shocks.
Schilke P., Walmsley C.M., Pineau des Forets G., Flower D.R.
<Astron. Astrophys. 321, 293 (1997)>
=1997A&A...321..293S 1997A&A...321..293S (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; Atomic physics
Keywords: molecular processes - shock waves -
ISM: abundances; jets and outflows; molecules
Abstract:
We study the production of SiO in the gas phase of molecular outflows,
through the sputtering of Si-bearing material in grains. The
sputtering is driven by neutral particle impact on charged grains in
C-type shocks, at the speed corresponding to ambipolar diffusion.
Shock speeds in the range 10<vs<40km/s and preshock densities
104<nH<107cm-3 have been investigated. Sputtering of
Si-bearing material in both the cores and the mantles of the grains is
considered. We find that, for vs of approximately 25km/s and nH of
the order 105cm-3, column densities of SiO similar to those
observed in molecular out flow regions can be generated by either
mechanism. Impact by particles heavier than helium dominates the
core-sputtering process for shock velocities of this order. The
profiles of rotational transitions of SiO are computed and compared
with observations of molecular outflows.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1a 72 30 *Mantle and dissociative sputtering parameters
table1b 72 12 *Dissociation on impact parameters
table2 80 100 Rate coefficient parameters, for gas-phase
reactions involving Si-bearing species
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Note to table1a and table1b: Parameters adopted when computing the rate
coefficients for reactions involving grains
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Byte-by-byte Description of file: table1a
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Bytes Format Units Label Explanations
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1 A1 --- Type [ab] a: mantle sputtering,
b: dissociative sputtering
3- 15 A13 --- R1 Beginning species of the reaction (1)
17- 37 A21 --- R2 Resulting species of the reaction
39- 45 E7.2 --- S Sputtering yield factor
48- 52 F5.2 eV Eth Sputtering threshold energy
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Note (1): Asterisks denote species in grain mantles
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Byte-by-byte Description of file: table1b
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Bytes Format Units Label Explanations
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1 A1 --- Type [c] c: dissociation on impact
3- 15 A13 --- R1 Beginning species of the reaction
17- 37 A21 --- R2 Resulting species of the reaction
39- 45 E7.2 --- Y0 Multiplicative constant (1)
48- 52 F5.2 --- Ediss Dissociation energy (1)
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Note (1): The dissociative probability has an Arrhenius form, Y0exp(-Ediss/E),
where E is the impact energy, Ediss the dissociation energy and
Y0 the multiplicative constant
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Byte-by-byte Description of file: table2
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Bytes Format Units Label Explanations
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1- 14 A14 --- R1 Beginning species of the reaction
16- 32 A17 --- R2 Resulting species of the reaction
34- 41 E8.2 --- gamma Gamma coefficient (1)
44- 48 F5.2 --- alpha ? Alpha coefficient (1)
50- 56 F7.1 K beta ? Beta coefficient (1)
58 I1 --- Note ? Note (2)
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Note (1): Rate coefficient : gamma.(T/300)alpha.exp(-beta/T) cm3/s
Note (2): 1: Langer & Glassgold, 1990, ApJ 352, 123
2: Supposed to be the same as CH (Gredel, 1990)
3: MacKay, 1995MNRAS.274..694M 1995MNRAS.274..694M
4: UMIST ratefile (Millar et al., 1996, A&AS, in press)
5: Herbst (1995, private communication)
6: Elkin & Armentrout, 1984, J. Phys. Chem. 88, 5454
7: See the discussion of Flower et al., 1996MNRAS.280..447F 1996MNRAS.280..447F
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References:
Gredel R., 1990 in "Molecular astrophysics", Hartquist T.W. ed,
Cambridge University Press, Cambridge, p.305
(End) Patricia Bauer [CDS] 30-Sep-1996