Baade's window with APOGEE: Metallicities, ages and chemical abundances
  Baade's window (BW) is one of the most observed Galactic bulge fields in
terms of chemical abundances. Due to its low and homogeneous interstellar
absorption it is considered as a calibration field for Galactic bulge studies.
In the era of large spectroscopic surveys, calibration fields such as BW are
necessary to cross calibrate the stellar parameters and individual abundances
of the APOGEE survey. We use the APOGEE BW stars to derive their metallicity
distribution function (MDF) and individual abundances, for $\alpha$- and
iron-peak elements of the APOGEE ASPCAP pipeline (DR13), as well as the age
distribution for stars in BW. We determine the MDF of APOGEE stars in BW and
find a remarkable agreement with that of the Gaia-ESO survey (GES). Both
exhibit a clear bimodal distribution. We also find that the Mg-metallicity
planes of both surveys agree well, except for the metal-rich part ([Fe/H]
>0.1), where APOGEE finds systematically higher Mg abundances with respect to
the GES. The ages based on the [C/N] ratio reveal a bimodal age distribution,
with a major old population at 10 Gyr, with a decreasing tail towards younger
stars. A comparison between APOGEE estimates and stellar parameters, and those
determined by other sources reveals detectable systematic offsets, in
particular for spectroscopic surface gravity estimates. In general, we find a
good agreement between individual abundances of O, Na, Mg, Al, Si, K, Ca, Cr,
Mn, Co, and Ni from APOGEE with that of literature values. We have shown that
in general APOGEE data show a good agreement in terms of MDF and individual
chemical abundances with respect to literature works. Using the [C/N] ration we
found a significant fraction of young stars in BW which is in agreement with
the model of Haywood et al. (2016).
