EDP Sciences Journals List
Advanced Search
Subscriber Authentication Point
Home All issues Volume 441/1 Article
Free access article

Issue A&A
Volume 441, Number 1, October I 2005
Page(s) 249 - 260
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20041711



A&A 441, 249-260 (2005)
DOI: 10.1051/0004-6361:20041711

A 3-5 $\mathsf{\mu}$m VLT spectroscopic survey of embedded young low mass stars II

Solid OCN $\mathsf{^{-}}$
F. A. van Broekhuizen1, K. M. Pontoppidan2, H. J. Fraser1 and E. F. van Dishoeck1, 2

1  Raymond and Beverly Sackler Laboratory for Astrophysics, Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands
    e-mail: fvb$@$strw.leidenuniv.nl
2  Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands

(Received 22 July 2004 / Accepted 31 May 2005 )

Abstract
The 4.62 $\mu$m (2164.5 cm-1) "XCN" band has been detected in the M-band spectra of 34 deeply embedded young stellar objects (YSO's), observed with high signal-to-noise and high spectral resolution with the VLT-ISAAC spectrometer, providing the first opportunity to study the solid OCN- abundance toward a large number of low-mass YSO's. It is shown unequivocally that at least two components, centred at 2165.7 cm-1 (FWHM = 26 cm-1) and 2175.4 cm-1 (FWHM = 15 cm-1), underlie the XCN band. Only the 2165.7-component can be ascribed to OCN-, embedded in a strongly hydrogen-bonding, and possibly thermally annealed, ice environment based on laboratory OCN- spectra. In order to correct for the contribution of the 2175.4-component to the XCN band, a phenomenological decomposition into the 2165.7- and the 2175.4-components is used to fit the full band profile and derive the OCN- abundance for each line-of-sight. The same analysis is performed for 5 high-mass YSO's taken from the ISO-SWS data archive. Inferred OCN- abundances are $\leq$0.85% toward low-mass YSO's and $\leq$1% toward high-mass YSO's, except for W33 A. Abundances are found to vary by at least a factor of 10-20 and large source-to-source abundance variations are observed within the same star-forming cloud complex on scales down to 400 AU, indicating that the OCN- formation mechanism is sensitive to local conditions. The inferred abundances allow quantitatively for photochemical formation of OCN-, but the large abundance variations are not easily explained in this scenario unless local radiation sources or special geometries are invoked. Surface chemistry should therefore be considered as an alternative formation mechanism.


Key words: astrochemistry -- line: identification -- line: profiles -- molecular data -- ISM: abundances -- ISM: lines and bands

SIMBAD Objects



© ESO 2005


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.