The galactic abundance gradient from Cepheids -: IV.: New results for the outer disc

As a continuation of our previous work on the abundance gradient in the outer part of the galactic disc, this paper presents results on the metallicicty distribution over galactocentric distances up to 15 kpc. The outer disc is clearly separated from the middle part by the existence of a step in the metallicity distribution at about 10 kpc. Taking the region of galactocentric distances from 10 kpc to 15 kpc, one can derive an iron gradient - 0.03 +/- 0.01 dex kpc(-1) (25 stars). The existence of a discontinuity can be caused by the effective suppression of mixing processes near the corotation circle where the radial component of the gas velocity should be very small.