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A. W. Stephens, J. A. Frogel (OSU), R. Davies (U. Durham), W. Freedman, C. Gallart (Carnegie Obs.), P. Jablonka (Obs. de Paris-Meudon), S. Ortolani (U. di Padova), A. Renzini (ESO), R.M. Rich (UCLA)
We have obtained JHK images of 5 bulge fields and 5 metal-rich globular clusters in M31 with the NICMOS camera NIC2 on the Hubble Space Telescope. The globulars we have observed are G1, G170, G174, G177 & G280. We calibrate our data using the NICMOS transformations determined by Stephens et al. (1999). For each cluster and field we have created a color-magnitude diagram for the upper 6-8 magnitudes of the giant branch, and determined their bolometric luminosity function. Higher spatial resolution and deeper J band observations taken in parallel with NIC1 are used to evaluate the effects of crowding on our primary observations.
From these observations we estimate the metallicity for each cluster and field. We also compare the giant branches of the M31 globulars and bulge field with those of ground-based observations of the giant branches of globular clusters and fields in the Galactic bulge.
Our data resolve the long standing controversy regarding the presence of luminous giants -- and by implication an intermediate age population in M31's bulge. These data will help further our understanding of the evolution of metal rich stars, and improve population synthesis models meant to study the stellar content of distant, unresolvable bulges and elliptical galaxies.
Support for this work was provided by NASA through grant number GO-7826 and GO-7876 from the Space Telescope Science Institute.
The author(s) of this abstract have provided an email address for comments about the abstract: stephens@astronomy.ohio-state.edu