L134N Revisited

Abstract

L134N is a cold, starless cloud, very high above the galactic plane,close to us and well delineated in continuum dust emission maps. Thiscloud is considered to be representative of oxygen rich dark clouds(with the presence of SO, SO₂, NO, ...). It is thus a goodreference together with TMC-1 to test astrochemical models. Thanks toISO, SCUBA and near IR wide field cameras, the detailed study of thedust has become possible in such cold and dark clouds. In parallel,progress in radiotelescope receiver sensitivity now allows to map weaklines on large surfaces. We have thus started a project to study bothdust and a few gaseous key species (CO, CS, SO and N₂H⁺) toaddress several questions. We want to assess the quantity of dust andgas all over the cloud, study possible C¹⁸O and/or C¹⁷Odepletion towards dense cores, evaluate the structure of the gas, theabundance of CS and SO to possibly estimate the chemical age of thecloud (time dependent models show that the CS/SO ratio diminishes withtime) and evaluate the rare isotope abundances, especially ¹⁷Oand ³⁴S in a first step. To constrain the molecular abundanceswith the highest possible confidence, we have observed severaltransitions for each species and each isotopomer. Though we haveobserved far less species than Dickens et al. [1], wehave done it on a larger area, including thus the strongest C¹⁸Opeak and two other peaks, with a better signal-to-noise ratio. Most ofthe data are already acquired. We present here preliminary results.