Galactic evolution of nitrogen

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

Corresponding author: G. Israelian, gil@ll.iac.es

Received: 23 January 2004
Accepted: 23 March 2004

Abstract

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 with the slope . 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 Lyα systems. This is the first direct comparison of the (N/O) ratios in these objects with those in Galactic stars.