Mikhaela Gallardo (Graduate Institute of Astronomy, National Central University, Taiwan); W. P. Chen (Graduate Institute of Astronomy, National Central University, Taiwan) Yue-Huan Lee (Graduate Institute of Astronomy, National Central University, Taiwan); Chien-Hsiu Lee (Subaru Telescope, National Astronomical Observatory of Japan, Hawaii, USA)
A star cluster in formation is shaped by the morphology and conditions of the parental molecular cloud, which is usually filamentary and patchy. Encounters among member stars virializes the system that lead to mass segregation, for which massive members “sink” to the core, while the low-mass members occupy larger volumes, with the least-massive members slowly “evaporated”. The cluster becomes less gravitationally bound, and eventually would be disintegrated. Berkeley 17 is among the oldest Galactic open clusters, with an age 10 Gyr rivaling those of globular clusters. How such longevity is possible surviving the exacerbating tidal disruption orbiting in the Galactic disk is currently unknown. The cluster is noted to resemble globular clusters with its sub-solar metallicity, an excessive number of blue stragglers, and a prominent horizontal branch. Previous analysis indicated a core-tail morphology, with relatively low-mass members in the tail, a manifestation of tidal stripping in this dissolving cluster. This study presents the latest imaging data, with a 1-deg field in g and r bands, from WIYN, a 3.5-meter telescope atop Kitt Peak in southern Arizona, USA. Our WIYN data are some 1.5 mag deeper, reaching g~22.5 mag, than the Pan-STARRS data used in the previous study, allowing us to probe even less massive members (> 0.5 solar masses). We will present color-magnitude diagram of the cluster region in comparison with those of nearby “comparison” fields so as to diagnose the member population versus escaped then-members of this aged cluster.