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We present high-quality spectrophotometric observations of 15 supergiant H II regions in 14 new low-metallicity blue compact galaxies (BCGs) selected mainly from the First and Second Byurakan Surveys and with oxygen abundance 12 + log O/H between 7. 37 and 8. 04 (Zₛun₅/35 =10 Mₛun_) stars. The dispersion of the N/O ratio is found to be remarkably small, being only +/-0. 08 in the log. This can only be understood if primary N is produced in massive stars, not in intermediate-mass (4 Mₛun_ <= M <= 9 Mₛun_) stars as commonly thought. BCGs show the same O/Fe overabundance with respect to the Sun (~0. 34 in the log) as galactic halo stars, suggesting the same chemical enrichment history, and supporting the scenario of an early enrichment of the galactic halo by massive Population III stars. We have compared the observed heavy element abundance ratios with theoretical yields from current massive star nucleosynthesis models from Weaver & Woosley (1993). The small dispersion in the heavy element abundance ratios suggests that there is not a large IMF variation between BCGs with different metallicities.
Thuan et al. (Mon,) studied this question.