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Far-infrared dust opacity and visible extinction

Published online by Cambridge University Press:  25 September 2002

M. Giard ,
J.P. Bernard ,
A. Klotz ,
I. Ristorcelli ,
L. Cambrésy ,
F. Boulanger ,
G. Lagache  and
B. Stepnik
L. Cambrésy
Affiliation:
Infrared Processing and Analysis Center, Jet Propulsion Laboratory, California Institute of Technology, Mail Code 100-22, Pasadena, CA 91125, USA
F. Boulanger
Affiliation:
Institut d'Astrophysique Spatiale, Université Paris Sud, Bât. 121, 91405 Orsay Cedex, France
G. Lagache
Affiliation:
Institut d'Astrophysique Spatiale, Université Paris Sud, Bât. 121, 91405 Orsay Cedex, France
B. Stepnik
Affiliation:
Institut d'Astrophysique Spatiale, Université Paris Sud, Bât. 121, 91405 Orsay Cedex, France
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Abstract

We present an extinction map of the Polaris molecular cirrus cloud derivedfrom star counts and compare it with the Schlegel et al. [13]extinction map derived from the far-infrared dust opacity. We find that,within the Polaris cloud, the Schlegel et al. [13] AV values are,on average, a factor 2 higher than the star count values. We propose that thisdiscrepancy results from a difference in τFIR/AV between the diffuseatomic medium and the Polaris cloud. We use the difference in spectral energydistribution, warm for the diffuse atomic medium, cold for the Polaris cloud,to separate their respective contribution to the line of sight integratedinfrared emission and find that the τFIR/AV of cold dust in Polarisis on average 4 times higher than the Schlegel et al. [13] value fordust in atomic cirrus. This change in dust property could be interpreted bya growth of fluffy particles within low opacity molecular cirrus clouds suchas Polaris. Our work suggests that variations in dust emissivity must betaken into account to estimate AV from dust emission wherever coldinfrared emission is present (i.e. molecular clouds).

Type
Research Article
Information
European Astronomical Society Publications Series , Volume 4: Infrared and Submillimeter Space Astronomy: An International Colloquium to Honor the Memory of Guy Serra , 2002 , pp. 291
Copyright
© EAS, EDP Sciences, 2002

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