Structure of L 1521B: CO observations of a dense core in Taurus

L 1521B is a dense core near B216 in one of the long filaments of the Taurus molecular cloud complex. The core is not associated with any known IR sources and shows no apparent signs of star formation. We have mapped the cloud in 13CO(1–0) and C18O(1–0) using a grid of 1′. This area, altogether some 140 square arc minutes, contains the density maximum as well as some parts of the filament north-west of the cloud centre. At the centre position we derive a column density N(C18O)=4·1015cm−2 and an optical depth of about 1.3 for C18O.Using a value of r=140 pc for the distancewe estimate that the total mass contained within a radius of 3′ around the density maximum is about 20 solar masses. The visual extinction has been estimated from the C18O column density and through star counts of two fields observed at 2.2μm. The extinction in the central region is AV ≈ 20m. We have also mapped part of the B216 filament about one degree north-west of the centre of L 1521B in C18O(1–0). This area contains two IRAS point sources which are probably associated with class I protostars.