CaltechAUTHORS
Published September 10, 2007 | Version Published
Journal Article Open

The Relationship between the Optical Depth of the 9.7 μm Silicate Absorption Feature and Infrared Differential Extinction in Dense Clouds

Creators

  • 1. ROR icon Search for Extraterrestrial Intelligence
  • 2. ROR icon Ames Research Center
  • 3. ROR icon Infrared Processing and Analysis Center
  • 4. ROR icon The University of Texas at Austin
  • 5. ROR icon Smithsonian Astrophysical Observatory
  • 6. ROR icon Jet Propulsion Lab
  • 7. ROR icon Rensselaer Polytechnic Institute

Abstract

We have examined the relationship between the optical depth of the 9.7 μm silicate absorption feature (τ_(9.7)) and the near-infrared color excess, E(J - K_s), in the Serpens, Taurus, IC 5146, Chameleon I, Barnard 59, and Barnard 68 dense clouds/cores. Our data set, based largely on Spitzer IRS spectra, spans E(J - K_s) = 0.3-10 mag (corresponding to visual extinction between about 2 and 60 mag). All lines of sight show the 9.7 μm silicate feature. Unlike in the diffuse ISM where a tight linear correlation between the 9.7 μm silicate feature optical depth and the extinction (A_V) is observed, we find that the silicate feature in dense clouds does not show a monotonic increase with extinction. Thus, in dense clouds, τ_(9.7) is not a good measure of total dust column density. With few exceptions, the measured τ_(9.7) values fall well below the diffuse ISM correlation line for E(J - K_s) > 2 mag (A_V > 12 mag). Grain growth via coagulation is a likely cause of this effect.

Additional Information

© 2007 The American Astronomical Society. Received 2007 May 23; accepted 2007 July 23; published 2007 August 20. This work is based (in part) on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. Support for this work was provided by NASA. The authors thank the referee, Viktor Zubko, for his helpful suggestions. Facilities: Spitzer(IRS).

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Identifiers

Eprint ID
16508
Resolver ID
CaltechAUTHORS:20091028-110429977

Funding

NASA

Dates

Created
2009-11-02
Created from EPrint's datestamp field
Updated
2021-11-08
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