The oxygen abundance distribution in M 101

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 R-23-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)(T e) abundance distribution. The parameters of the (O/H)(R 23) abundance distribution differ significantly from those of the (O/H)(T e) abundance distribution: the central (O/H)(R 23) oxygen abundance is higher by around 0.4 dex and the gradient is steeper by a factor of around 1.5 as compared to those values in the (O/H)(T e) abundance distribution. The dispersion in (O/H)(P) abundance at fixed radius is rather small, similar to0.08 dex, and is equal to that in (O/H)(T e) abundance. The dispersion in (O/H)(R 23) abundance at fixed radius is appreciably larger, similar to0.16 dex, compared to that in (O/H)(T e) abundance. It has been shown that the extra dispersion in (O/H)(R 23) abundances is an artifact and reflects scatter in excitation parameter P at fixed radius.