  The NASA space telescope Kepler has provided unprecedented time-series
observations which have revolutionised the field of asteroseismology, i.e. the
use of stellar oscillations to probe the interior of stars. The Kepler-data
include observations of stars in open clusters, which are particularly
interesting for asteroseismology. One of the clusters observed with Kepler is
NGC 6811, which is the target of the present paper. However, apart from
high-precision time-series observations, sounding the interiors of stars in
open clusters by means of asteroseismology also requires accurate and precise
atmospheric parameters as well as cluster membership indicators for the
individual stars. We use medium-resolution (R~25,000) spectroscopic
observations, and three independent analysis methods, to derive effective
temperatures, surface gravities, metallicities, projected rotational velocities
and radial velocities, for 15 stars in the field of the open cluster NGC 6811.
We discover two double-lined and three single-lined spectroscopic binaries.
Eight stars are classified as either certain or very probable cluster members,
and three stars are classified as non-members. For four stars, cluster
membership could not been assessed. Five of the observed stars are G-type
giants which are located in the colour-magnitude diagram in the region of the
red clump of the cluster. Two of these stars are surely identified as red clump
stars for the first time. For those five stars, we provide chemical abundances
of 31 elements. The mean radial-velocity of NGC 6811 is found to be
+6.68$\pm$0.08 km s$^{-1}$ and the mean metallicity and overall abundance
pattern are shown to be very close to solar with an exception of Ba which we
find to be overabundant.
