EDP Sciences Journals List
Advanced Search
Subscriber Authentication Point
Home All issues Volume 467/1 Article
Free access article

Issue A&A
Volume 467, Number 1, May III 2007
Page(s) 179 - 186
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20066670



A&A 467, 179-186 (2007)
DOI: 10.1051/0004-6361:20066670

Depletion and low gas temperature in the L183 (=L134N) prestellar core: the N2H+-N2D+ tool

L. Pagani1, A. Bacmann2, S. Cabrit1, and C. Vastel3

1  LERMA & UMR 8112 du CNRS, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France
    e-mail: laurent.pagani@obspm.fr
2  Universite Bordeaux 1, CNRS, OASU, UMR 5804, 33270 Floirac, France
3  Centre d'Étude Spatiale des Rayonnements, 9 avenue du Colonel Roche, BP 4346, 31029 Toulouse Cedex, France

(Received 31 October 2006 / Accepted 26 January 2007)

Abstract
Context.The study of pre-stellar cores (PSCs) suffers from a lack of undepleted species to trace the physical properties of the gas in their very dense inner parts.
Aims.We carry out detailed modelling of N2H+ and N2D+ cuts across the L183 main core to evaluate the depletion of these species and their usefulness as a probe of physical conditions in PSCs.
Methods.We have developed a non-LTE (NLTE) Monte-Carlo code treating the 1D radiative transfer of both N2H+ and N2D+, making use of recently published collisional coefficients with He between individual hyperfine levels. The code includes line overlap between hyperfine transitions. An extensive set of core models is calculated and compared with observations. Special attention is paid to the issue of source coupling to the antenna beam.
Results.The best-fitting models indicate that i) gas in the core center is very cold (7 $\pm$ 1 K) and thermalized with dust; ii) depletion of N2H+ does occur, starting at densities 5-7$\times$105 cm-3 and reaching a factor of $ 6^{\rm +13}_{\rm -3}$ in abundance; iii) deuterium fractionation reaches ~70% at the core center; and iv) the density profile is proportional to r-1 out to ~4000 AU, and to r-2 beyond.
Conclusions.Our NLTE code could be used to (re-)interpret recent and upcoming observations of N2H+ and N2D+ in many pre-stellar cores of interest, to obtain better temperature and abundance profiles.


Key words: ISM: abundances -- ISM: molecules -- radiative transfer -- ISM: structure -- ISM: individual objects: L183 -- line: formation



© ESO 2007


What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.