Ices and the Extinction Curve in the Quiescent Medium of Isolated Dense Cores

Details Ices and the Extinction Curve in the Quiescent Medium of Isolated Dense Cores Ices and the Extinction Curve in the Quiescent Medium of Isolated Dense Cores

Jan 2012

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21934921b&link_type=abstract

American Astronomical Society, AAS Meeting #219, #349.21

Astronomy and Astrophysics

Astronomy

Scientific paper

For a sample of 31 stars behind isolated dense cores, ground-based and Spitzer spectra and photometry in the 1-25 um wavelength range are combined. We use this unique dataset to (1) investigate the composition of the ices before Young Stellar Objects (YSOs) are formed and (2) determine the 'high resolution' extinction curve.
We find that the strengths of the 6.0 and 6.85 um ice absorption bands are in line with those of YSOs. Thus, their carriers, which, besides H2O and CH3OH, may include NH4+, HCOOH, H2CO, and NH3, are readily formed in the dense core phase. The 3.53 um C-H stretching mode of solid CH3OH was discovered. The CH3OH/H2O abundance ratios of 5%-12% are larger than upper limits in the Taurus molecular cloud. The initial ice composition therefore depends on the environment. Signs of thermal and energetic processing that were found toward some YSOs are absent in the ices toward background stars.
Furthermore, the extinction curve is derived empirically from the 1-25 um spectra. Its high resolution allows for the separation of continuum and feature extinction. The extinction between 13 and 25 um is 50% relative to that at 2.2 um. This probably indicates the presence of a population of large grains (RV>=5.5). However, the peak optical depth of the 9.7 um band of silicates relative to the continuum extinction at 2.2 um is significantly shallower than in the diffuse ISM. This extends the results of Chiar et al. to a larger sample and higher extinctions.

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