  NGC 6809 is a luminous metal-poor halo globular cluster that is relatively
easy to study due to its proximity and low concentration. Because of its high
Galactic latitude (b = -23deg), interstellar reddening and contamination is not
very high. We aim to determine the relative proper motion and membership
probability of the stars in the wide area of globular cluster NGC 6809. To
target cluster members reliably during spectroscopic surveys and both spatial
and radial distributions in the cluster outskirts without including field
stars, a good proper motion and membership probability catalogue of NGC 6809 is
required.The archival data of two epochs with a time-base line of 7.1 years
have been collected with Wide Field Imager (WFI) mounted on the 2.2m MPG/ESO
telescope. The CCD images of both epochs have been reduced using the
astrometric techniques as described in Anderson et al. (2006). The calibrated
UBVI magnitudes have been derived using Stetson's secondary standard stars. We
derived the relative proper motion and membership probabilities for \sim 12600
stars in the field of globular cluster NGC 6809. The measurement error in
proper motions for the stars of V \sim 17 mag is 2.0 mas/yr, gradually
increasing up to \sim 3 mas/yr at V = 20 mag. We also provide the membership
probability for the published different types of sources in NGC 6809. An
electronic catalogue with proper motion and membership probability for the
stars will be available to the astronomical community.
