The Chemical Evolution of Galaxies by Successive Starbursts
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We propose an evolutionary scenario by successive bursts of star formation to reproduce the chemical properties of massive nearby Starburst Nucleus Galaxies (SBNGs). The N/O abundance ratios in SBNGs are 0.2 dex higher than in normal HII regions observed in the disks of late-type spirals. The variation of the N/O ratio as a function of metallicity follows a "primary + secondary" relation, but the increase of nitrogen does not appear as a continuous process. Assuming that nitrogen is produced by intermediate-mass stars, we show that our observations are consistent with a model where the bulk of nitrogen in SBNGs was formed during past sequences of bursts of star formation which probably started 2 or 3 Gyrs in the past.
Contributed talk to the 34th Rencontres de Moriond, 13-20 March 1999, ``Building Galaxies: from the Primordial Universe to the Present'', ed F. Hammer, T. X. Thuan, V. Cayatte, B. Guiderdoni & J. Tran Thanh Van (Ed. Frontieres). 4 pages including 2 figures
Contributed talk to the 34th Rencontres de Moriond, 13-20 March 1999, ``Building Galaxies: from the Primordial Universe to the Present'', ed F. Hammer, T. X. Thuan, V. Cayatte, B. Guiderdoni & J. Tran Thanh Van (Ed. Frontieres). 4 pages including 2 figures