EDP Sciences
Free access
Volume 421, Number 2, July II 2004
Page(s) 649 - 658
Section Galactic structure, stellar clusters and populations
DOI http://dx.doi.org/10.1051/0004-6361:20047132

A&A 421, 649-658 (2004)
DOI: 10.1051/0004-6361:20047132

Galactic evolution of nitrogen

G. Israelian1, A. Ecuvillon1, R. Rebolo1, 2, R. García-López1, 3, P. Bonifacio4 and P. Molaro4

1  Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
2  Consejo Superior de Investigaciones Científcas, Spain
3  Departamento de Astrofísica, Universidad de La Laguna, Av. Astrofísico Francisco Sánchez s/n, 38206 La Laguna, Tenerife, Spain
4  Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34131 Trieste, Italy

(Received 23 January 2004 / Accepted 23 March 2004 )

We present detailed spectroscopic analysis of nitrogen abundances in 31 unevolved metal-poor stars analysed by spectral synthesis of the near-UV NH band at 3360 Å observed at high resolution with various telescopes. We found that [N/Fe] scales with that of iron in the metallicity range $-3.1 <\rm [Fe/H]<0$ with the slope $0.01\pm0.02$. Furthermore, we derive uniform and accurate (N/O) ratios using oxygen abundances from near-UV OH lines obtained in our previous studies. We find that a primary component of nitrogen is required to explain the observations. The NH lines are discovered in the VLT/UVES spectra of the very metal-poor subdwarfs G64-12 and LP815-43 indicating that these stars are N rich. The results are compared with theoretical models and observations of extragalactic H II regions and Damped Ly $\alpha$ systems. This is the first direct comparison of the (N/O) ratios in these objects with those in Galactic stars.

Key words: stars: abundances -- galaxies: abundances

Offprint request: G. Israelian, gil@ll.iac.es

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