The $Gaia$-ESO Survey: the inner disk intermediate-age open cluster NGC
  6802
  Milky Way open clusters are very diverse in terms of age, chemical
composition, and kinematic properties. Intermediate-age and old open clusters
are less common, and it is even harder to find them inside the solar
Galactocentric radius, due to the high mortality rate and strong extinction
inside this region. NGC 6802 is one of the inner disk open clusters (IOCs)
observed by the $Gaia$-ESO survey (GES). This cluster is an important target
for calibrating the abundances derived in the survey due to the kinematic and
chemical homogeneity of the members in open clusters. Using the measurements
from $Gaia$-ESO internal data release 4 (iDR4), we identify 95 main-sequence
dwarfs as cluster members from the GIRAFFE target list, and eight giants as
cluster members from the UVES target list. The dwarf cluster members have a
median radial velocity of $13.6\pm1.9$ km s$^{-1}$, while the giant cluster
members have a median radial velocity of $12.0\pm0.9$ km s$^{-1}$ and a median
[Fe/H] of $0.10\pm0.02$ dex. The color-magnitude diagram of these cluster
members suggests an age of $0.9\pm0.1$ Gyr, with $(m-M)_0=11.4$ and
$E(B-V)=0.86$. We perform the first detailed chemical abundance analysis of NGC
6802, including 27 elemental species. To gain a more general picture about
IOCs, the measurements of NGC 6802 are compared with those of other IOCs
previously studied by GES, that is, NGC 4815, Trumpler 20, NGC 6705, and
Berkeley 81. NGC 6802 shows similar C, N, Na, and Al abundances as other IOCs.
These elements are compared with nucleosynthetic models as a function of
cluster turn-off mass. The $\alpha$, iron-peak, and neutron-capture elements
are also explored in a self-consistent way.
