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Date and Time of the Query: 2019-08-17 T16:20:29 PDT
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For refcode 2003A&A...397..487P:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
2003A&A...397..487P On the origin of nitrogen L. S. Pilyugin, T. X. Thuan, J. M. Vilchez 1 - Main Astronomical Observatory of National Academy of Sciences of Ukraine, 27 Zabolotnogo str., 03680 Kiev, Ukraine 2 - Astronomy Department, University of Virginia, Charlottesville, VA 22903, USA 3 - Instituto de Astrofisica de Andalucia, Apdo, 3004, 18080 Granada, Spain Received 30 May 2002 / Accepted 30 September 2002 Abstract. The problem of the origin of nitrogen is considered within the framework of an empirical approach. The oxygen abundances and nitrogen to oxygen abundances ratios are derived in H II regions of a number of spiral galaxies through the recently suggested P-method using more than six hundred published spectra. The N/O-O/H diagram for H II regions in irregular and spiral galaxies is constructed. It is found that the N/O values in H II regions of spiral galaxies of early morphological types are higher than those in H II regions with the same metallicity in spiral galaxies of late morphological types. This suggests a long-time-delayed contribution to the nitrogen production. The N/O ratio of a galaxy can then be used as an indicator of the time that has elapsed since the bulk of star formation occurred, or in other words of the nominal "age" of the galaxy as suggested by Edmunds & Pagel more than twenty years ago. The scatter in N/O values at a given O/H can be naturally explained by differences in star formation histories in galaxies. While low-metallicity dwarf galaxies with low N/O do not contain an appreciable amount of old stars, low-metallicity dwarf galaxies with an appreciable fraction of old stars have high N/O. Consideration of planetary nebulae in the Small Magellanic Cloud and in the Milky Way Galaxy suggests that the contribution of low-mass stars to the nitrogen production is significant, confirming the conclusion that there is a long-time-delayed contribution to the nitrogen production. Key words: galaxies: abundances - galaxies: ISM - galaxies: spiral - galaxies: irregular
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