NGC 1252: a high altitude, metal poor open cluster remnant
  If stars form in clusters but most stars belong to the field, understanding
the details of the transition from the former to the latter is imperative to
explain the observational properties of the field. Aging open clusters are one
of the sources of field stars. The disruption rate of open clusters slows down
with age but, as an object gets older, the distinction between the remaining
cluster or open cluster remnant (OCR) and the surrounding field becomes less
and less obvious. As a result, finding good OCR candidates or confirming the
OCR nature of some of the best candidates still remains elusive. One of these
objects is NGC 1252, a scattered group of about 20 stars in Horologium. Here we
use new wide-field photometry in the UBVI pass-bands, proper motions from the
Yale/San Juan SPM 4.0 catalogue and high resolution spectroscopy concurrently
with results from N-body simulations to decipher NGC 1252's enigmatic
character. Spectroscopy shows that most of the brightest stars in the studied
area are chemically, kinematically and spatially unrelated to each other.
However, after analysing proper motions, we find one relevant kinematic group.
This sparse object is relatively close (about 1 kpc), metal poor and is
probably not only one of the oldest clusters (3 Gyr) within 1.5 kpc from the
Sun but also one of the clusters located farthest from the disc, at an altitude
of nearly -900 pc. That makes NGC 1252 the first open cluster that can be truly
considered a high Galactic altitude OCR: an unusual object that may hint at a
star formation event induced on a high Galactic altitude gas cloud. TW Hor and
HD 20286 are unlikely to be part of NGC 1252. NGC 1252 17 is identified as an
unrelated, Population II cannonball star moving at about 400 km/s.
