Cécile Gry 1 & Emmanuel Caux 2
1 LAS, BP 8, F-13376 Marseille cedex 12
2 CESR, BP 4346, F-31028 Toulouse cedex 04
We present a study of a very diffuse phase of the interstellar
medium with LWS observations of three cirrus presenting contras-
ting characteristics. They were observed as part of the LWS
central program.
Five distinct positions were chosen in each cirrus to sample
parts of the cloud differing in terms of ratio of neutral to
molecular gas or distribution of dust particule size.
The data have been reprocessed with the latest LWS off-line
processing software and analysed with ISAP and LIA. The various
processing steps especially needed for faint and extended sources
will be presented in some detail, especially the continuum extrac-
tion after correction for the dark and the background emission.
We also include for comparison and complement a large sample of
diffuse medium observations : 15 galactic lines of sight and 36
off-positions for stellar observations.
Line intensities will be given for the detectable lines (in the
cirrus [CII] 158 
is always detected and
sometimes [OI] 145 ,
[OI] 63
and [NII] 122 .
The line intensities show good correlations with the total far-
IR emission. On the other hand, they do not show a proportionality
dependence on the mid-IR emission. These relationships and the
dependence of line emissions with other dust and gas properties
will be discussed in terms of the role of different factors in
the heating/cooling of the diffuse medium.