Chemical Abundances of M giants in the Galactic Center: a Single
  Metal-Rich Population with Low [alpha/Fe]
  Context. The formation and evolution of the Milky Way bulge is still largely
an unanswered question. One of the most essential observables needed in its
modelling are the metallicity distribution and the trends of the alpha elements
as measured in stars. While Bulge regions beyond R > 50 pc of the centre has
been targeted in several surveys, the central part has escaped detailed study
due to the extreme extinction and crowding. The abundance gradients from the
center are, however, of large diagnostic value. Aims. We aim at investigating
the Galactic Centre environment by probing M giants in the field, avoiding
supergiants and cluster members. Methods. For 9 field M-giants in the Galactic
Centre region, we have obtained high- and low-resolution spectra observed
simultaneously with CRIRES and ISAAC on UT1 and UT3 of the VLT. The
low-resolution spectra provide a means of determining the effective
temperatures, and the high-resolution spectra provide detailed abundances of
Fe, Mg, Si, and Ca. Results. We find a metal-rich population at
[Fe/H]=+0.11+-0.15 and a lack of the metal-poor population, found further out
in the Bulge, corroborating earlier studies. Our [alpha/Fe] element trends,
however, show low values, following the outer Bulge trends. A possible
exception of the [Ca/Fe] trend is found and needs further investigation.
Conclusions. The results of the analysed field M-giants in the Galactic Centre
region, excludes a scenario with rapid formation, in which SNIIe played a
dominated role in the chemical enrichment of the gas. The metal-rich
metallicities together with low alpha-enhancement seems to indicate a bar-like
population perhaps related to the nuclear bar.
