REVISITING THE ABUNDANCE GRADIENT IN THE MASER HOST GALAXY NGC 4258

New spectroscopic observations of 36 H II regions in NGC 4258 obtained with the Gemini telescope are combined with existing data from the literature to measure the radial oxygen abundance gradient in this galaxy. The [OIII]lambda 4363 auroral line was detected in four of the outermost targets (17-22 kpc from the galaxy center), allowing a determination of the electron temperature T-e of the ionized gas. From the use of different calibrations of the R-23 abundance indicator, an oxygen abundance gradient of approximately -0.012 +/- 0.002 dex kpc (1) is derived. Such a shallow gradient, combined with the difference in the distance moduli measured from the Cepheid period-luminosity relation by Macri et al. between two distinct fields in NGC 4258, would yield an unrealistically strong effect of metallicity on the Cepheid distances. This strengthens the suggestion that systematic biases might affect the Cepheid distance of the outer field. Evidence for a similar effect in the differential study of M33 by Scowcroft et al. is presented. A revision of the transformation between strong-line and T-e-based abundances in Cepheid-host galaxies is discussed. In the T-e abundance scale, the oxygen abundance of the inner field of NGC 4258 is found to be comparable with the LMC value.