Issue |
A&A
Volume 449, Number 1, April I 2006
|
|
---|---|---|
Page(s) | 251 - 265 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20052931 | |
Published online | 16 March 2006 |
VLT-ISAAC 3–5 μm spectroscopy of embedded young low-mass stars
III. Intermediate-mass sources in Vela
1
Sterrenkundig Instituut Anton Pannekoek, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands e-mail: ewine@strw.leidenuniv.nl
2
Leiden Observatory, PO Box 9513, 2300, Leiden, The Netherlands
3
ESA Research Fellow, Research Support Science Department, ESTEC, Keplerlaan 1, PO 2201 AZ, Noordwijk, The Netherlands
4
Astrochimie Expérimentale, Institut d'Astrophysique Spatiale, Université Paris-Sud, Bât. 121, 91405 Orsay Cedex, France
5
Divisions of Geological and Planetary Sciences, California Institute of Technology, Passadena, CA 91125, USA
6
Department of Physics, University of Strathclyde, John Anderson Building, 107 Rottenrow, Glasgow G4 ONG, UK
Received:
24
February
2005
Accepted:
28
November
2005
Aims.We study in this paper the ice composition in the envelope around intermediate-mass class I Young Stellar Objects (YSOs).Methods.We performed a spectroscopic survey toward
five intermediate-mass class I YSOs located in the Southern Vela molecular cloud in the L
(2.85–4.0 μm) and M (4.55–4.8 μm) bands at resolving
powers –800 up to 10 000, using the
Infrared Spectrometer and Array Camera mounted on the Very
Large Telescope-ANTU. Lower mass companion objects were observed
simultaneously in both bands.Results.Solid
H
O at 3 μm is detected in all sources,
including the companion objects. CO ice at 4.67 μm is detected
in a few main targets and one companion object. One object
(LLN 19) shows little CO ice but strong
gas-phase CO ro-vibrational lines in absorption. The CO ice profiles are
different from source to source. The amount of water ice and CO
ice trapped in a water-rich mantle may correlate with the flux
ratio at 12 and 25 μm. The abundance of H2O-rich CO likely
correlates with that of water ice. A weak
feature at 3.54 μm attributed to solid CH
OH and a
broad feature near 4.62 μm are observed toward LLN 17, but not toward the other sources.
The derived abundances
of solid CH
OH and OCN- are ~
%
and ~
% of the H
O ice abundance
respectively.
The H
O optical depths do not show an increase with
envelope mass, nor do they show lower values for the companion objects compared
with the main protostar. The line-of-sight CO ice abundance does not
correlate with the source bolometric luminosity.Conclusions.Comparison of the solid CO profile toward
LLN 17, which shows an
extremely broad CO ice feature, and that of its lower mass
companion at a few thousand AU, which exhibits a narrow profile,
together with the detection of OCN- toward LLN 17
provide direct evidences for local thermal processing of the ice.
© ESO, 2006
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