SIMBAD references

The well-observed spiral galaxy M 101 was considered. The radial distributions of oxygen abundances determined in three different ways (with the classic T_e-method, with the R₂₃-method, and with the P-method) were compared. It was found that the parameters (the central oxygen abundance and the gradient) of the radial (O/H)_P abundance distribution are close to those of the (O/H)_Te abundance distribution. The parameters of the (O/H)_R23 abundance distribution differ significantly from those of the (O/H)_Te abundance distribution: the central (O/H)_R23 oxygen abundance is higher by around 0.4dex and the gradient is steeper by a factor of around 1.5 as compared to those values in the (O/H)_Te abundance distribution. The dispersion in (O/H)_P abundance at fixed radius is rather small, ∼0.08dex, and is equal to that in (O/H)_Te abundance. The dispersion in (O/H)_R23 abundance at fixed radius is appreciably larger, ∼0.16dex, compared to that in (O/H)_Te abundance. It has been shown that the extra dispersion in (O/H)_R23 abundances is an artifact and reflects scatter in excitation parameter P at fixed radius.