CNO behaviour in planet-harbouring stars. I Nitrogen abundances in stars
  with planets
  Carbon, nitrogen, and oxygen (CNO) are key elements in stellar formation and
evolution, and their abundances should also have a significant impact on
planetary formation and evolution. We present a detailed spectroscopic analysis
of 74 solar-type stars, 42 of which are known to harbour planets. We determine
the nitrogen abundances of these stars and investigate a possible connection
between N and the presence of planetary companions. We used VLT/UVES to obtain
high-resolution near-UV spectra of our targets. Spectral synthesis of the NH
band at 3360A was performed with the spectral synthesis codes MOOG and FITTING.
We identify several spectral windows from which accurate N abundance can be
obtained. Nitrogen distributions for stars with and without planets show that
planet hosts are nitrogen-rich when compared to single stars. However, given
the linear trend between [N/Fe] vs [Fe/H], this fact can be explained as being
due to the metal-rich nature of planet hosts. We conclude that reliable N
abundances can be derived for metal-rich solar type stars from the near UV
molecular band at 3360A. We confirm a linear trend between [N/Fe] and
metallicity expected from standard models of Galactic chemical evolution.
