The metal contents of two groups of galaxies
  The hot gas in clusters and groups of galaxies is continuously being enriched
with metals from supernovae and stars. It is well established that the
enrichment of the gas with elements from oxygen to iron is mainly caused by
supernova explosions. The origins of nitrogen and carbon are still being
debated. Possible candidates include massive, metal-rich stars, early
generations of massive stars, intermediate or low mass stars and Asymptotic
Giant Branch (AGB) stars. In this paper we accurately determine the metal
abundances of the gas in the groups of galaxies NGC 5044 and NGC 5813, and
discuss the nature of the objects that create these metals.
  We mainly focus on carbon and nitrogen. We use spatially-resolved
high-resolution X-ray spectroscopy from XMM-Newton. For the spectral fitting,
multi-temperature hot gas models are used. The abundance ratios of carbon over
oxygen and nitrogen over oxygen that we find are high compared to the ratios in
the stars in the disk of our Galaxy. The oxygen and nitrogen abundances we
derive are similar to what was found in earlier work on other giant ellipticals
in comparable environments. We show that the iron abundances in both our
sources have a gradient along the cross-dispersion direction of the Reflection
Grating Spectrometer (RGS). We conclude that it is unlikely that the creation
of nitrogen and carbon takes place in massive stars, which end their lives as
core-collapse supernovae, enriching the medium with oxygen because oxygen
should then also be enhanced. Therefore we favour low-and intermediate mass
stars as sources of these elements. The abundances in the hot gas can best be
explained by a 30-40% contribution of type Ia supernovae based on the measured
oxygen and iron abundances and under the assumption of a Salpeter Initial Mass
Function (IMF).
