2005/11/15 by C. Knez, A. C. A. Boogert, K. M. Pontoppidan +9 · 4 citations
Chemistry · Physics and Astronomy · #Astrophysics and Star Formation Studies #Molecular Spectroscopy and Structure #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/499584
published as Astrophys.J.635:L145-L148,2005 · 4 pages, 5 figures; To appear in Astrophysical Journal Letters
arxiv created 2005/11/15 · openalex publication_date 2005/12/07 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
A powerful way to directly observe the solid-state inventory of dense molecular clouds is by infrared spectroscopy of background stars. We present Spitze r IRS 5-20 μm spectra of ices toward stars behind the Serpens and Taurus molecular clouds, probing visual extinctions of 10-34 mag. These data provide the first complete inventory of solid-state material in dense clouds before star formation begins. The spectra show prominent 6.0 and 6.85 μm bands. In contrast to some young stellar objects (YSOs), most (~75%) of the 6.0 μm band is explained by the bending mode of pure H 2 O ice. In realistic mixtures this number increases to 85%, because the peak strength of the H 2 O bending mode is very sensitive to the molecular environment. The strength of the 6.85 μm band is comparable to what is observed toward YSOs. Thus, the production of the carrier of this band does not depend on the energetic input of a nearby source. The spectra show large abundances of CO and CO 2 (20%-40% with respect to H 2 O ice). Compared with YSOs, the band profile of the 15 μm CO 2 bending mode lacks the signatures of crystallization, confirming the cold, pristine nature of these lines of sight. After the dominant species are removed, there are residuals that suggest the presence of minor species such as HCOOH and possibly NH 3 . Clearly, models of star formation should begin with dust models already coated with a fairly complex mixture of ices.