L134N Revisited

L134N is a cold, starless cloud, very high above the galactic plane, close to us and well delineated in continuum dust emission maps. This cloud is considered to be representative of oxygen rich dark clouds (with the presence of SO, SO_2, NO, ...). It is thus a good reference together with TMC-1 to test astrochemical models. Thanks to ISO, SCUBA and near IR wide field cameras, the detailed study of the dust has become possible in such cold and dark clouds. In parallel, progress in radiotelescope receiver sensitivity now allows to map weak lines on large surfaces. We have thus started a project to study both dust and a few gaseous key species (CO, CS, SO and N_2H^+) to address several questions. We want to assess the quantity of dust and gas all over the cloud, study possible C^(18)O and/or C^(17)O depletion towards dense cores, evaluate the structure of the gas, the abundance of CS and SO to possibly estimate the chemical age of the cloud (time dependent models show that the CS/SO ratio diminishes with time) and evaluate the rare isotope abundances, especially ^(17)O and ^(34)S in a first step. To constrain the molecular abundances with the highest possible confidence, we have observed several transitions for each species and each isotopomer. Though we have observed far less species than Dickens et al. [1], we have done it on a larger area, including thus the strongest C^(18)O peak and two other peaks, with a better signal-to-noise ratio. Most of the data are already acquired. We present here preliminary results