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Published September 2004 | Submitted + Published
Journal Article Open

Spitzer Space Telescope Spectroscopy of Ices toward Low-Mass Embedded Protostars


Sensitive 5-38 μm Spitzer Space Telescope and ground-based 3-5 μm spectra of the embedded low-mass protostars B5 IRS1 and HH 46 IRS show deep ice absorption bands superposed on steeply rising mid-infrared continua. The ices likely originate in the circumstellar envelopes. The CO_2 bending mode at 15 μm is a particularly powerful tracer of the ice composition and processing history. Toward these protostars, this band shows little evidence for thermal processing at temperatures above 50 K. Signatures of lower temperature processing are present in the CO and OCN^- bands, however. The observed CO2 profile indicates an intimate mixture with H_(2)O, but not necessarily with CH_(3)OH, in contrast to some high-mass protostars. This is consistent with the low CH_(3)OH abundance derived from the ground-based L-band spectra. The CO_2 : H_(2)O column density ratios are high in both B5 IRS1 and HH 46 IRS (~35%). Clearly, the Spitzer spectra are essential for studying ice evolution in low-mass protostellar environments and for eventually determining the relation between interstellar and solar system ices.

Additional Information

© 2004 American Astronomical Society. Received 2004 March 26; accepted 2004 May 13. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The VLT ISAAC spectra were obtained at the European Southern Observatory, Paranal, Chile, in the observing program 272.C-5008. Support for this work, part of the Spitzer Space Telescope Legacy Science Program, was provided by NASA through contracts 1224608 and 1230780 issued by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407. Astrochemistry in Leiden is supported by a NWO Spinoza grant and a NOVA grant.

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