MAJORS II: HCO⁺and HCN abundances in W40

We present observations of HCN and HCO J = in the central region of the W40 massive star-forming region. The observations were taken as part of a pilot project for the MAJORS large program at the JCMT telescope. By incorporating prior knowledge of N(H) and, assuming a constant density, and using the radex radiative transfer code we found that the HCN and HCO abundances range from X(HCN) = and X(HCO) =. Additional modelling using the nautilus chemical evolution code, which takes H density variations into account, however, suggests that the HCN and HCO abundances may be fairly constant. Careful modelling of three different positions finds X(HCN) = and X(HCO) =. Cross-comparison of the two models also provides a crude estimate of the gas density producing the HCN and HCO emission, with H densities in the range - cm, suggesting that the HCN and HCO emission does indeed arise from dense gas. High UV intensity (e.g. $]]> a few thousand) has no effect on the abundances in regions where the visual extinction is large enough to effectively shield the gas from the UV field. In regions where, however, the abundance of both species is lowered due to destructive reactions with species that are directly affected by the radiation field.