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Session 35 - Old Stellar Populations Beyond the Milky Way - I.
Oral session, Wednesday, June 11
North Main Hall A,
We have used the Wide Field Planetary Camera 2 on the Hubble Space Telescope to image star clusters in the halo of the nearby spiral galaxy M33. Our sample consists of 10 clusters which have been selected to have red colors, halo kinematics, a range of metallicities, and a range of projected locations in M33. Our main aim has been to construct color-magnitude diagrams of these clusters in order to estimate their metallicities and ascertain the morphology of their horizontal branches (HBs). Of the 8 clusters for which observations have been obtained, 7 show "HBs" that are essentially clumps lying on top of, or slightly blueward, of the giant branch. Yet, the metallicities of these clusters span the range --1.6 to --1.0 in [Fe/H]. As a result, there appears to be something fundamentally different about these clusters as compared with Galactic globular clusters with the same metallicities. In particular, we will discuss the possibility that the M33 halo clusters may be several gigayears younger than similar clusters in the Milky Way.
Program listing for Wednesday