Results of a spectrophotometric survey in the magellanic barred galaxy NGC 2366 and in the small weakly barred spiral galaxy NGC 4395, employing imaging spectrophotometry with narrow-band interference filters in the lines of Hα, Hβ, [O III] λ5007 and [N II] λ6584, are presented. The use of [O III]/Hβ as an abundance indicator is assessed; it is shown that for the probable range of the physical properties of the H II regions in NGC 2366 and NGC 4395, [O III]/Hβ may not give reliable estimates of O/H abundances in the interstellar gas in these two low-mass galaxies. Instead we use [NII]/[O III], which is more dependable at relatively low abundances. The derived mean levels of O/H (+/-1 σ dispersion) in NGC 2366 and NGC 4395 are 12 + log O/H = 8.19 +/- 0.14 and 8.33 +/- 0.25, respectively; the global gradients of both galaxies are flat. Mechanisms which could explain the absence of abundance gradients in low-mass and irregular galaxies are explored.
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Roy et al. (1996) studied this question.