2016MNRAS.456.2126S

Physical properties were derived for the candidate open cluster La Serena 94, recently unveiled by the VISTA Variables in the Vía Láctea (VVV) survey. Thanks to the exquisite angular resolution provided by Gemini South multiconjugate adaptive optics system/Gemini South Adaptive Optics Imager (GeMS/GSAOI), we could characterize this system in detail, for the first time, with deep photometry in JHKs bands. Decontaminated JHKs diagrams reach about 5 mag below the cluster turnoff in H. The locus of red clump giants in the colour-colour diagram, together with an extinction law, was used to obtain an average extinction of AV = 14.18±0.71. The same stars were considered as standard candles to derive the cluster distance, 8.5±1.0 kpc. Isochrones were matched to the cluster colour-magnitude diagrams to determine its age, logt(yr) = 9.12±0.06, and metallicity, Z = 0.02±0.01. A core radius of rc = 0.51±0.04 pc was found by fitting King models to the radial density profile. By adding up the visible stellar mass to an extrapolated mass function, the cluster mass was estimated as M=(2.65±0.57)×10^3 M_☉, consistent with an integrated magnitude of M_K_s=-5.82±0.16 and a tidal radius of rt = 17.2±2.1 pc. The overall characteristics of La Serena 94 confirm that it is an old open cluster located in the Crux spiral arm towards the fourth Galactic quadrant and distant 7.30±0.49 kpc from the Galactic Centre. The cluster distorted structure, mass segregation and age indicate that it is a dynamically evolved stellar system.