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The c2d Spitzer Spectroscopic Survey of Ices Around Low-Mass Young Stellar Objects: I. H2O and the 5-8 um Bands | | A. Boogert
; K. Pontoppidan
; C. Knez
; F. Lahuis
; J. Kessler-Silacci
; E. van Dishoeck
; G. Blake
; J. Augereau
; S. Bisschop
; S. Bottinelli
; T. Brooke
; J. Brown
; A. Crapsi
; N. Evans II
; H. Fraser
; V. Geers
; T. Huard
; J. Jorgensen
; K. Oberg
; L. Allen
; P. Harvey
; D. Koerner
; L. Mundy
; D. Padgett
; A. Sargent
; K. Stapelfeldt
; | | Date: |
8 Jan 2008 | | Abstract: | With the goal to study the physical and chemical evolution of ices in
solar-mass systems, a spectral survey is conducted of a sample of 41 low
luminosity YSOs using 3-38 um Spitzer and ground-based spectra. The long-known
6.0 and 6.85 um bands are detected toward all sources, with the Class 0-type
YSOs showing the deepest bands ever observed. In almost all sources the 6.0 um
band is deeper than expected from the bending mode of pure solid H2O. The depth
and shape variations of the remaining 5-7 um absorption indicate that it
consists of 5 independent components, which, by comparison to laboratory
studies, must be from at least 8 different carriers. Simple species are
responsible for much of the absorption in the 5-7 um region, at abundances of
1-30% for CH3OH, 3-8% for NH3, 1-5% for HCOOH, ~6% for H2CO, and ~0.3% for
HCOO- with respect to solid H2O. The 6.85 um band likely consists of one or two
carriers, of which one is less volatile than H2O because its abundance relative
to H2O is enhanced at lower H2O/tau_9.7 ratios. It does not survive in the
diffuse interstellar medium (ISM), however. The similarity of the 6.85 um bands
for YSOs and background stars indicates that its carrier(s) must be formed
early in the molecular cloud evolution. If an NH4+ salt is the carrier its
abundance with respect to solid H2O is typically 7%, and low temperature
acid-base chemistry or cosmic ray induced reactions must have been involved in
its formation. Possible origins are discussed for the carrier of an enigmatic,
very broad absorption between 5 and 8 um. Finally, all the phenomena observed
for ices toward massive YSOs are also observed toward low mass YSOs, indicating
that processing of the ices by internal ultraviolet radiation fields is a minor
factor in the early chemical evolution of the ices. [abridged] | | Source: | arXiv, 0801.1167 | | Services: | Forum | Review | PDF | Favorites | |
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