Issue |
A&A
Volume 376, Number 1, September II 2001
|
|
---|---|---|
Page(s) | 254 - 270 | |
Section | The Sun | |
DOI | https://doi.org/10.1051/0004-6361:20010936 | |
Published online | 15 September 2001 |
Ice absorption features in the 5-8 μm region toward embedded protostars *
1
Kapteyn Astronomical Institute, PO Box 800, 9700 AV Groningen, The Netherlands
2
SRON, PO Box 800, 9700 AV Groningen, The Netherlands
3
CalTech, Mail code 320-47, 1200 E. California Blvd., Pasadena, CA 91125, USA
4
Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands
5
Department of Physics, Applied Physics & Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180, USA
Corresponding author: J. V. Keane, jacquie@astro.rug.nl
Received:
23
December
1999
Accepted:
27
June
2001
We have obtained 5-8 spectra towards 10 embedded
protostars using the Short Wavelength Spectrometer on board
the Infrared Space Observatory (ISO-SWS) with the aim of studying the
composition of interstellar ices. The spectra are dominated
by absorption bands at 6.0
and 6.85 μm. The observed peak
positions, widths and relative intensities of these bands vary
dramatically along the different lines of sight. On the basis of
comparison with laboratory spectra, the bulk of the 6.0
absorption band is assigned to amorphous H2O ice. Additional
absorption, in this band, is seen toward 5 sources on the short
wavelength wing, near 5.8 μm, and the long wavelength side near
6.2 μm. We attribute the short wavelength absorption to
a combination of formic acid (HCOOH) and formaldehyde (H2CO),
while the long wavelength absorption has been assigned to the C-C
stretching mode of aromatic structures.
From an analysis of the 6.85
band, we conclude that this band is
composed of two components: a volatile component centered
near 6.75
and a more refractory component at 6.95 μm.
From a comparison with various temperature tracers of the thermal
history of interstellar ices, we conclude that the two 6.85
components are related through thermal processing.
We explore several possible carriers of the 6.85
absorption band, but no satisfactory identification can be made at present.
Finally, we discuss the possible implications for the
origin and evolution of interstellar ices that arise from these new results.
Key words: ISM: dust, extinction / ISM: molecules / ISM: abundances / infrared: ISM / stars: formation
© ESO, 2001
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