NGC?2419-ANOTHER REMNANT OF ACCRETION BY THE MILKY WAY*

摘要

We isolate a sample of 43 upper red giant branch stars in the extreme outer halo Galactic globular cluster (GC) NGC?2419 from two Keck/DEIMOS slitmasks. The probability that there is more than one contaminating halo field star in this sample is extremely low. Analysis of moderate-resolution spectra of these cluster members, as well as of our Keck/HIRES high-resolution spectra of a subsample of them, demonstrates that there is a small but real spread in Ca abundance of ~0.2?dex within this massive metal-poor GC. This provides additional support to earlier suggestions that NGC?2419 is the remnant of a dwarf galaxy accreted long ago by the Milky Way.