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S. Lacour, P. Sonnentrucker (JHU), R. Ferlet, M. Andre, J-M. Desert (IAP), E. Roueff, F. Le Petit (OBSPM)
We present new detections of the HD molecule along 12 sightlines going through translucent clouds. The formation of HD in gas phase is initiated by cosmic rays and the molecule is destroyed by photodissociation. Being less abundant than H2, its self shielding is less efficient. Therefore HD is only present in the inner regions of PDR. The sensitivity of {\em FUSE} allows to observe denser media than previously done with FUV-instruments, making it less elusive for studies (Ferlet et al 2000). Moreover, the {\em FUSE} bandwith (905 Å to 1187 Å) covers up to five usuable J=0 HD lines. It has been shown also that the abundance of HD is directly proportionnal to both \eta (the cosmic ray rate) and D/H near the core of the cloud (Black & Dalgarno 1978, Wright and Morton 1979). Thus, by measuring the HD/H2 ratio, we access the chemistry of the deepest region of the translucent cloud as well as its structure.
The author(s) of this abstract have provided an email address for comments about the abstract: lacour@pha.jhu.edu