NGC 6940 has hundreds of members. The cluster is quite scattered and in between its members are also visible field stars. For example, two bright stars, an 8.6 mag B8III giant star at the NE edge and a 9.1 mag A0III giant at the SW corner of the cluster are too young to be true members of NGC 6940 and are probably background stars. The brightest star (lucida) of NGC 6940 is the
red giant FG Vulpeculae, a semiregular
variable star whose magnitude ranges from 9.0 to 9.5 every 80 days approximately. In NGC 6940 have been detected 8 variable stars whose variability is consistent with the
delta Scuti variables. A study of the cluster by
ROSAT in
soft X-rays revealed four sources that are identified as cluster members. Three of these sources were identified as
binary stars, from a total of six known to exist in the cluster. The luminosity of the sources was typical of
RS Canum Venaticorum variables, close binaries that could retain very active coronal sources despite the age of the cluster. == References ==