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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 (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:
FileName Lrecl Records Explanations
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
Note to table1a and table1b: Parameters adopted when computing the rate coefficients for reactions involving grains Byte-by-byte Description of file: table1a
Bytes Format Units Label Explanations
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
Note (1): Asterisks denote species in grain mantles
Byte-by-byte Description of file: table1b
Bytes Format Units Label Explanations
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)
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
Byte-by-byte Description of file: table2
Bytes Format Units Label Explanations
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)
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 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
References: Gredel R., 1990 in "Molecular astrophysics", Hartquist T.W. ed, Cambridge University Press, Cambridge, p.305
(End) Patricia Bauer [CDS] 30-Sep-1996
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