Chemical modeling of L183 (L134N): an estimate of the ortho/para H{_2} ratio - CNRS - Centre national de la recherche scientifique Accéder directement au contenu
Article Dans Une Revue Astronomy and Astrophysics - A&A Année : 2009

Chemical modeling of L183 (L134N): an estimate of the ortho/para H{_2} ratio

L. Pagani
C. Vastel
  • Fonction : Auteur
E. Hugo
  • Fonction : Auteur
V. Kokoouline
  • Fonction : Auteur
C. H. Greene
  • Fonction : Auteur
Estelle Bayet
  • Fonction : Auteur
R. Peng
  • Fonction : Auteur
S. Schlemmer
  • Fonction : Auteur

Résumé

Context: The high degree of deuteration observed in some prestellar cores depends on the ortho-to-para H2 ratio through the H3+ fractionation. Aims: We want to constrain the ortho/para H2 ratio across the L183 prestellar core. This is required to correctly describe the deuteration amplification phenomenon in depleted cores such as L183 and to relate the total (ortho+para) H2D+ abundance to the sole ortho-H2D+ column density measurement. Methods: To constrain this ortho/para H2 ratio and derive its profile, we make use of the N2D^+/N2H+ ratio and of the ortho-H2D+ observations performed across the prestellar core. We use two simple chemical models limited to an almost totally depleted core description. New dissociative recombination and trihydrogen cation-dihydrogen reaction rates (including all isotopologues) are presented in this paper and included in our models. Results: We estimate the H2D+ ortho/para ratio in the L183 cloud, and constrain the H2 ortho/para ratio: we show that it varies across the prestellar core by at least an order of magnitude, being still very high (≈0.1) in most of the cloud. Our time-dependent model indicates that the prestellar core is presumably older than 1.5-2 × 105 years but that it may not be much older. We also show that it has reached its present density only recently and that its contraction from a uniform density cloud can be constrained. Conclusions: A proper understanding of deuteration chemistry cannot be attained without taking into account the whole ortho/para family of molecular hydrogen and trihydrogen cation isotopologues as their relations are of utmost importance in the global scheme. Tracing the ortho/para H2 ratio should also place useful constraints on the dynamical evolution of prestellar cores. Appendices A and B are only available in electronic form at http://www.aanda.org

Dates et versions

hal-00479878 , version 1 (03-05-2010)

Identifiants

Citer

L. Pagani, C. Vastel, E. Hugo, V. Kokoouline, C. H. Greene, et al.. Chemical modeling of L183 (L134N): an estimate of the ortho/para H{_2} ratio. Astronomy and Astrophysics - A&A, 2009, 494, pp.623. ⟨10.1051/0004-6361:200810587⟩. ⟨hal-00479878⟩
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