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Session 71 - Globular Clusters.
Display session, Wednesday, January 15
We present deep (V \simeq 27) HST\//WFPC2 V- and I-band color--magnitude diagrams, and derive structural parameters, for the bright globular star clusters (GCs) G302 and G312 located in the halo of M31. We find that G302 is a metal-poor GC comparable to the Galactic GC NGC 6397 while G312 is roughly as metal-rich as 47 Tuc. Our results show no evidence for the presence of a young or intermediate-aged stellar population in either GC and neither GC exhibits the second parameter effect in its horizontal branch morphologies. Star counts and integrated light were used to fit two-dimensional Michie--King models to each GC. G312 has a normal Michie--King distribution of stars with a central concentration of c \sim 1.8 and a King core radius of r_c \sim 0\farcs15 (\sim 0.5 pc). G302 shows evidence for having undergone core-collapse. Both G302 and G312 have formal Michie--King tidal radii of r_t \sim 10\arcsec (\sim 35 pc). G302 shows evidence of having an elliptical tidal tail extending to \sim 2 to 3 times the formal tidal radius.
Program listing for Wednesday