EDP Sciences Journals List
Advanced Search
Subscriber Authentication Point
Home All issues Volume 386/3 Article
Free access article

Issue A&A
Volume 386, Number 3, May II 2002
Page(s) 1074 - 1102
Section Diffuse matter in space
DOI http://dx.doi.org/10.1051/0004-6361:20020362



A&A 386, 1074-1102 (2002)
DOI: 10.1051/0004-6361:20020362

CO and H $\mathsf{_2}$O vibrational emission toward Orion Peak 1 and Peak 2

E. González-Alfonso1, 2, C. M. Wright3, 4, J. Cernicharo1, D. Rosenthal5, A. M. S. Boonman3 and E. F. van Dishoeck3

1  CSIC, IEM, Dpto. Física Molecular, Serrano 123, 28006 Madrid, Spain
2  Universidad de Alcalá de Henares, Departamento de Física, Campus Universitario, 28871 Alcalá de Henares, Madrid, Spain
3  Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands
4  School of Physics, University College, Australian Defence Force Academy, University of New South Wales, Canberra ACT 2600, Australia
5  Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, 85741 Garching, Germany

(Received 4 December 2001 / Accepted 4 March 2002)

Abstract
ISO/SWS observations of Orion Peak 1 and Peak 2 show strong emission in the ro-vibrational lines of CO v=1-0 at 4.45-4.95  $\mu$m and of H 2O $\nu_2=1{-}0$ at 6.3-7.0  $\mu$m. Toward Peak 1 the total flux in both bands is, assuming isotropic emission, $\approx$2.4 and $\approx$0.53 , respectively. This corresponds to $\approx$14 and $\approx$3% of the total luminosity in the same beam. Two temperature components are found to contribute to the CO emission from Peak 1/2: a warm component, with $T_{\rm k}=200$-400 K, and a hot component with $T_{\rm k}\sim3\times10^3$ K. At Peak 2 the CO flux from the warm component is similar to that observed at Peak 1, but the hot component is a factor of $\approx$2 weaker. The band is $\approx$25% stronger toward Peak 2, and seems to arise only in the warm component. The P-branch emission of both bands from the warm component is significantly stronger than the R-branch, indicating that the line emission is optically thick. Neither thermal collisions with nor with H I seem capable of explaining the strong emission from the warm component. Although the emission arises in the postshock gas, radiation from the most prominent mid-infrared sources in Orion BN/KL is most likely pumping the excited vibrational states of CO and . CO column densities along the line of sight of $N{\rm (CO)}=5$- $10\times10^{18}~cm^2$ are required to explain the band shape, the flux, and the , and beam-filling is invoked to reconcile this high N(CO) with the upper limit inferred from the emission. CO is more abundant than by a factor of at least 2. The density of the warm component is estimated from the  emission to be ~ $2\times 10^7~cm^3$. The CO emission from the hot component is neither satisfactorily explained in terms of non-thermal (streaming) collisions, nor by resonant scattering. Vibrational excitation through collisions with for densities of ~ $3\times 10^8~cm^3$ or, alternatively, with atomic hydrogen, with a density of at least 107 cm3, are invoked to explain simultaneously the emission from the hot component and that from the high excitation lines in the same beam. A jump shock is most probably responsible for this emission. The emission from the warm component could in principle be explained in terms of a C-shock. The underabundance of relative to CO could be the consequence of  photodissociation, but may also indicate some contribution from a jump shock to the CO warm emission.


Key words: shock waves -- ISM: abundances -- ISM: individual objects: Orion

Offprint request: E. González-Alfonso, gonzalez@isis.iem.csic.es

SIMBAD Objects



© ESO 2002


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.