2001A&A...378.1024C


C.D.S. - SIMBAD4 rel 1.7 - 2021.05.06CEST21:03:36

2001A&A...378.1024C - Astronomy and Astrophysics, volume 378, 1024-1036 (2001/11-2)

Gas-grain chemical models of star-forming molecular clouds as constrained by ISO and SWAS observations.

CHARNLEY S.B., RODGERS S.D. and EHRENFREUND P.

Abstract (from CDS):

We have investigated the gaseous and solid state molecular composition of dense interstellar material that periodically experiences processing in the shock waves associated with ongoing star formation. Our motivation is to confront these models with the stringent abundance constraints on CO2, H2O and O2, in both gas and solid phases, that have been set by ISO and SWAS. We also compare our results with the chemical composition of dark molecular clouds as determined by ground-based telescopes. Beginning with the simplest possible model needed to study molecular cloud gas-grain chemistry, we only include additional processes where they are clearly required to satisfy one or more of the ISO-SWAS constraints. When CO, N2 and atoms of N, C and S are efficiently desorbed from grains, a chemical quasi-steady-state develops after about one million years. We find that accretion of CO2and H2O cannot explain the [CO2/H2O ] ice ISO observations; as with previous models, accretion and reaction of oxygen atoms are necessary although a high O atom abundance can still be derived from the CO that remains in the gas. The observational constraints on solid and gaseous molecular oxygen are both met in this model. However, we find that we cannot explain the lowest H2O abundances seen by SWAS or the highest atomic carbon abundances found in molecular clouds; additional chemical processes are required and possible candidates are given. One prediction of models of this type is that there should be some regions of molecular clouds which contain high gas phase abundances of H2O, O2 and NO. A further consequence, we find, is that interstellar grain mantles could be rich in NH2OH and NO2. The search for these regions, as well as NH2OH and NO2 in ices and in hot cores, is an important further test of this scenario. The model can give good agreement with observations of simple molecules in dark molecular clouds such as TMC-1 and L134N. Despite the fact that S atoms are assumed to be continously desorbed from grain surfaces, we find that the sulphur chemistry independently experiences an ``accretion catastrophe''. The S-bearing molecular abundances cease to lie within the observed range after about 3x106 years and this indicates that there may be at least two efficient surface desorption mechanisms operating in dark clouds - one quasi-continous and the other operating more sporadically on this time-scale. We suggest that mantle removal on short time-scales is mediated by clump dynamics, and by the effects of star formation on longer time-scales. The applicability of this type of dynamical-chemical model for molecular cloud evolution is discussed and comparison is made with other models of dark cloud chemistry.

Abstract Copyright:

Journal keyword(s): molecular abundances - astrochemistry - molecular processes

Simbad objects: 16

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Number of rows : 16

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2021
#notes
1 NAME Taurus Complex SFR 04 41.0 +25 52           ~ 3691 0
2 TMC-1 MoC 04 41 45.9 +25 41 27           ~ 1420 0
3 LDN 1544 DNe 05 04 16.6 +25 10 48           ~ 729 0
4 NAME [BM89] L1544 cor 05 04 22.5 +25 11 36           ~ 435 1
5 NAME OMC-1 MoC 05 35 14 -05 22.4           ~ 1055 2
6 [RLK73] IRc 2 IR 05 35 14.51548 -05 22 30.5943           ~ 592 1
7 NAME Orion Bright Bar reg 05 35 22.30 -05 24 33.0           ~ 754 0
8 NGC 2024 Cl* 05 41 43 -01 50.5           ~ 1087 1
9 LDN 183 MoC 15 54 12.2 -02 49 42           ~ 703 1
10 * rho Oph ** 16 25 35.11766 -23 26 49.8150 4.30 4.85 4.63 4.27 3.96 B2IV+B2V 617 0
11 NAME rho Oph A Cloud MoC 16 26 26.4 -24 22 33           ~ 251 1
12 Elia 2-29 Y*O 16 27 09.43032 -24 37 18.7716           ~ 269 1
13 [TS84] IRS 2 Y*O 19 01 41.569 -36 58 31.23           K2 78 0
14 NAME CrA Dark Cloud MoC 19 01 51 -36 58.9           ~ 412 0
15 LDN 663 DNe 19 36 55 +07 34.4           ~ 571 0
16 IRAS 23118+6110 Y*O 23 14 01.63 +61 27 20.2           ~ 350 0

    Equat.    Gal    SGal    Ecl

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2021.05.06-21:03:36

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