Ice, Dust and Extinction in Dense Clouds

Details Ice, Dust and Extinction in Dense Clouds Ice, Dust and Extinction in Dense Clouds

May 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011iaus..280p.126c&link_type=abstract

The Molecular Universe, Posters from the proceedings of the 280th Symposium of the International Astronomical Union held in Tole

Astronomy and Astrophysics

Astronomy

Scientific paper

We present the results of our ongoing study of ice evolution, dust properties and extinction in dense cores, dense clouds with varying levels of star formation activity, and young stellar objects (Chiar et al. 2007, 2011; Boogert et al. 2008, 2011). Our studies are based on 5 to 25 micron spectra from Spitzer's Infrared Spectrometer, 2 to 4 micron spectra from ground-based facilities (IRTF-SpeX, VLT-ISAAC, Keck-NIRSPEC), and 2 to 24 micron photometry from Spitzer and 2MASS. For the dense core and clouds, we use background field stars to probe the dense cloud environments. We used the K-band spectra, in conjunction with stellar photosphere models, to accurately classify the spectral type of the field stars, helping to better quantify the extinction curve across the full spectral range. For quiescent clouds as probed by field stars, we find that the extinction between 13 and 25 micron is 50% less than that at 2.2 micron. In addition to the continuum extinction that is well-fitted by our empirically derived extinction curve, we also analyzed the ice and dust features for each line of sight. The H2O-ice column is determined from the 3 micron band (where observed) and, where there is a high enough dust column, absorption features centered at 6.0 and 6.85 micron are observed. The 6.0 and 6.85 micron features likely have several carriers in addition to H2O-ice: CH3OH, NH4+, HCOOH, H2CO and NH3. These ice features show no signs of thermal or energetic processing of the ice species, unlike many YSO environments. The 3.53 and 9.7 micron stretching modes of CH3OH-ice are also detected in a few lines of sight. These are the first detections of CH3OH-ice in dense clouds unassociated with YSO environments. For our large sample, we have also substantiated the result by Chiar et al. (2007) that the ratio of the 9.7 micron silicate absorption to the near-IR color excess is smaller in dense clouds compared to the diffuse interstellar medium.

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