N. Marcelino, J. Cernicharo
We present IRAM 30m mapping observations around the cyanopolyyne peak of TMC-1, showing the spatial distribution of HCN, HCO+$, and their ^13C, $^ 15 N, 18 O, and D isotopologues. The less abundant 13 C, ^15N, and ^ 18 O isotopologues are distributed in a southeast--northwest filament, with emission peaks located east and south of the cyanopolyyne peak's position. While the deuterated substitutions show the same filamentary structure as the other isopologues, the main emission peak is located at the north of the filament. On the other hand, the main HCN and HCO+ species show a hole of emission southeast of the cyanopolyyne peak. Furthermore, HCN hyperfine components show relative intensities far from their local-thermodynamic-equilibrium (LTE) values. These effects are consistent with absorption and scattering from a surrounding envelope, which is also supported by the double-peak line profiles observed for HCN and HCO+. We constructed non-LTE models to try to reproduce the observed line profiles and obtain column densities in several positions along and across the filament. The source structure used in the models is formed by several adjacent spheres, each consisting of a central dense core and a surrounding envelope, with the core density increasing along the filament southeast to northwest. Maps of the D/H intensity ratio were obtained for DCN and DCO+, showing a higher deuteration degree towards the north of the filament, where the n( H _2) density is also largest according to our models. Other isotopic abundance ratios were computed using several isotopologues of HCN, HNC, and HCO+ observed in the deep 3,mm survey observations towards the centre of the map. The 12 C/^13C abundance ratio of 30±5 indicates fractionation of 13 C in both HCN and HNC. However, very different ^14N/^ 15 N abundance ratios are obtained for both species, 1140±456 and 176±60 for HCN and HNC, respectively. Hence, depletion of 15 N seems to follow different chemical paths for both isomers.