Far-infrared properties of high latitude cirrus clouds

R. J. Laureijs 1 - L. Haikala 2

1 ISO Science Operations Centre, Astrophysics Division of ESA, Villafranca, Apdo. 50727, E-28080 Madrid, Spain -
2 Observatory, P.O. Box 14, FIN-00014 University of Helsinki, Finland, and ESO

Abstract:

Far-infrared scans in the 60, 90, 135 and 200 tex2html_wrap_inline231 filter bands of ISOPHOT were obtained for 4 quiescent high latitude clouds. The targets have been selected from IRAS images and have different central opacities spanning a range from less than one to several magnitudes of visual extinction. For each cloud we find that the ratio between the emission in the C_135 and C_200 bands ( tex2html_wrap_inline233 ) is independent of the strength of the C_200 emission. This suggests that the observed dust temperature is constant throughout each cloud. On the other hand we find that tex2html_wrap_inline233 varies from cloud to cloud indicating global temperature variations between clouds. The 60 tex2html_wrap_inline231 emission was marginally detected. At 90 tex2html_wrap_inline221 m we have measured a significant decline in emission towards the centre of the clouds. This indicates that a fraction of the emission in the 90 tex2html_wrap_inline221 m band is due to a dust component different from the one giving rise to the 135 and 200 tex2html_wrap_inline221 m emission.

Keywords:
interstellar medium: dust, clouds


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