Y. H. Lee (Graduate Institute of Astronomy, National Central University, Taiwan); W.P. Chen (Graduate Institute of Astronomy, National Central University, Taiwan; Department of Physics, National Central University, Taiwan); M. Gallardo (Graduate Institute of Astronomy, National Central University, Taiwan); C.H. Lee (Subaru Telescope, National Astronomical Observatory of Japan)
Stars are formed in groups out of molecular clouds. As a star cluster ages, its members are dispersed as the consequences of internal stellar dynamics and external perturbations. Berkeley 17, with a heliocentric distance 2.7 kpc, is among the oldest known open clusters (~10 Gyr). With 2MASS and PAN-STARRS 1 data, the cluster has been diagnosed to have experienced mass segregation with low-mass stars (to 0.7 solar) being stripped away by Galactic tidal forces (Bhattacharya et al. 2017). Here we present the data observed with the WIYN 3.5-m telescope. With a 1-deg field of view, our images at g’ and r’ bands are about 1 to 1.5 magnitudes deeper than previously available, thereby allowing us to identify even lower-mass members, down to about 0.5 solar masses. The star-count technique has been applied to derive the size and shape of the cluster. We will show the spatial distribution of members of various masses, the mass function, and how stellar evaporation has proceeded in this dissolving star cluster.