The Magellanic Bridge cluster NGC 796: Deep optical AO imaging reveals
  the stellar content and initial mass function of a massive open cluster
  NGC 796 is a massive young cluster located 59 kpc from us in the diffuse
intergalactic medium of the 1/5-1/10 $Z_{\odot}$ Magellanic Bridge, allowing to
probe variations in star formation and stellar evolution processes as a
function of metallicity in a resolved fashion, providing a link between
resolved studies of nearby solar-metallicity and unresolved distant metal-poor
clusters located in high-redshift galaxies. In this paper, we present adaptive
optics $gri$H$\alpha$ imaging of NGC 796 (at 0.5", which is ~0.14 pc at the
cluster distance) along with optical spectroscopy of two bright members to
quantify the cluster properties. Our aim is to explore if star formation and
stellar evolution varies as a function of metallicity by comparing the
properties of NGC 796 to higher metallicity clusters. We find from isochronal
fitting of the cluster main sequence in the colour-magnitude diagram an age of
20$^{+12}_{-5}$ Myr. Based on the cluster luminosity function, we derive a
top-heavy stellar initial mass function (IMF) with a slope $\alpha$ =
1.99$\pm$0.2, hinting at an metallicity and/or environmental dependence of the
IMF which may lead to a top-heavy IMF in the early Universe. Study of the
H$\alpha$ emission line stars reveals that Classical Be stars constitute a
higher fraction of the total B-type stars when compared with similar clusters
at greater metallicity, providing some support to the chemically homogeneous
theory of stellar evolution. Overall, NGC 796 has a total estimated mass of
990$\pm200$ $M_{\odot}$, and a core radius of 1.4$\pm$0.3 pc which classifies
it as a massive young open cluster, unique in the diffuse interstellar medium
of the Magellanic Bridge.
