Query : 2018MNRAS.477.4454H

2018MNRAS.477.4454H - Mon. Not. R. Astron. Soc., 477, 4454-4472 (2018/July-2)

Modelling the molecular composition and nuclear-spin chemistryof collapsing pre-stellar sources.


Abstract (from CDS):

We study the gravitational collapse of pre-stellar sources and the associated evolution of their chemical composition. We use the University of Grenoble Alpes Astrochemical Network (UGAN), which includes reactions involving the different nuclear-spin states of H2, H_3+, and of the hydrides of carbon, nitrogen, oxygen, and sulphur, for reactions involving up to seven protons. In addition, species-to-species rate coefficients are provided for the ortho/para interconversion of the H_3^+ + H2 system and isotopic variants. The composition of the medium is followed from an initial steady state through the early phase of isothermal gravitational collapse. Both the freeze-out of the molecules on to grains and the coagulation of the grains were incorporated in the model. The predicted abundances and column densities of the spin isomers of ammonia and its deuterated forms are compared with those measured recently towards the pre-stellar cores H-MM1, L16293E, and Barnard B1. We find that gas-phase processes alone account satisfactorily for the observations, without recourse to grain-surface reactions. In particular, our model reproduces both the isotopologue abundance ratios and the ortho:para ratios of NH2D and NHD2 within observational uncertainties. More accurate observations are necessary to distinguish between full scrambling processes - as assumed in our gas-phase network - and direct nucleus- or atom-exchange reactions.

Abstract Copyright: © 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society

Journal keyword(s): Astrochemistry - Stars: formation - ISM: abundances, molecules - ISM: individual objects: H-MM1, L16293E, Barnard B1

Status at CDS : Large table(s) will be appraised for possible ingestion in VizieR.

Simbad objects: 4

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Number of rows : 4
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 Barnard 1 MoC 03 33 16.3 +31 07 51           ~ 313 0
2 [HKM99] B1-b cor 03 33 20.32 +31 07 21.5           ~ 197 0
3 JCMTSF J162758.6-243343 cor 16 27 58.3 -24 33 42           ~ 24 0
4 NAME IRAS 16293E cor 16 32 29.060 -24 29 10.27           ~ 56 1

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