OSO 20-m HCN 1–0 monitoring data towards 46P/Wirtanen in December 2018 and January 2019. The data points (blue marker with vertical lσ errors bars; horizontal bars indicate the range of observations), which are also listed in Table 4, represent the integrated intensity as a function of MJD or days from perihelion. The dashed lines represent the results from the radiative transfer modelling (see Sect. 4) using three different HCN production rates from 0.5 × 10²⁵mol s⁻¹ to 1.5 × 10²⁵ mol s⁻¹ as indicated for a temperature of 70 K and .