Planck 2018 results. VI. Cosmological parameters (Corrigendum)

In the original version, the bounds given in Eqs. (87a) and (87b) on the contribution to the early-time optical depth, τ(15, 30), contained a numerical error in deriving the 95th percentile from the Monte Carlo samples. The corrected 95% upper bounds are: τ(15, 30) < 0.018 (lowE, flat τ(15, 30), FlexKnot); (1) τ(15, 30) < 0.023 (lowE, flat knot, FlexKnot). (2) These bounds are a factor of ∼3 larger than the originally reported results. Consequently, the new bounds do not significantly improve upon previous results from Planck data presented in Millea & Bouchet (2018) as was stated, but are instead comparable. Equations (1) and (2) give results that are now similar to those of Heinrich & Hu (2021), who used the same Planck 2018 data to derive a 95 % upper bound of 0.020 using the principal component analysis (PCA) model and uniform priors on the PCA mode amplitudes.