Shortly after birth, open clusters start dissolving; gradually losing stars
into the surrounding star field. The time scale for complete disintegration
depends both on their initial membership and location within the Galaxy. Open
clusters undergoing the terminal phase of cluster disruption or open cluster
remnants (OCRs) are notoriously difficult to identify. From an observational
point, a combination of low number statistics and minimal contrast against the
general stellar field conspire to turn them into very challenging objects. To
make the situation even worst, random samples of field stars often display
features that may induce to classify them erroneously as extremely evolved open
clusters. In this paper, we provide a detailed study of the stellar content and
kinematics of NGC 6863, a compact group of a few stars located in Aquila and
described by the POSS as a non existent cluster. Nonetheless, this object has
been recently classified as OCR. The aim of the present work is to either
confirm or disprove its OCR status by a detailed star-by-star analysis. The
analysis is performed using wide-field photometry in the UBVI pass-band, proper
motions from the UCAC3 catalogue, and high resolution spectroscopy as well as
results from extensive N-body calculations. Our results show that the four
brightest stars commonly associated to NGC 6863 form an asterism, a group of
non-physically associated stars projected together, leading to the conclusion
that NGC 6863 is not a real open cluster.Comment: 10 pages, 8 eps figure, in press in Astronomy and Astrophysis.
Abstract shortened to fit i
