AAS 207th Meeting, 8-12 January 2006
Session 163 Star Formation Grab Bag I
Oral, Wednesday, 2:00-3:30pm, January 11, 2006, Wilson A/B

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[163.04] Spitzer Mid-infrared Spectroscopy of Ices toward Background Stars

C. Knez (University of Texas), A. C. A. Boogert, K. M. Pontoppidan (Caltech), J. E. Kessler-Silacci (University of Texas), E. F. van Dishoeck (Leiden Univesrity), N. J. Evans (University of Texas), J.-C. Augereau (Laboratoire d'Astrophysique, Grenoble), G. A. Blake (Caltech), F. Lahuis (SRON)

We present results from the c2d legacy project of ice absorption between 5-20 \mum toward the stars CK 2 behind the Serpens cloud and Elias 13 and 16 behind the Taurus cloud, probing extinctions in the range of 10-34 magnitudes. CK 2 and Elias 16 show prominent 6.0 and 6.85 \mum bands. In contrast to some young stellar objects (YSOs), most (~75%) of the 6.0 \mum band is explained by the bending mode of pure H2O ice. In realistic mixtures with CO2, this number increases to 85% because the peak strength of the H2O bending mode is very sensitive to the molecular environment. The 6.85 \mum band is a factor of 2 stronger toward Serpens compared to Taurus, when scaled to H2O ice. The variation between lines of sight as well as the absolute strength is comparable to observations toward YSOs. Thus, the production of the carrier of this band does not depend on energetic input of a nearby source. In both Serpens and Taurus, the sources show large abundances of CO2 (20-35% with respect to H2O ice). Compared to YSOs, the band profile of the 15 \mum CO2 bending mode lacks the signatures of crystallization, indeed confirming the cold, pristine nature of these lines of sight.

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Bulletin of the American Astronomical Society, 37 #4
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