We have obtained HST-NICMOS observations of five of M31's most metal-rich globular clusters: G1, G170, G174, G177 & G280. For the two clusters farthest from the nucleus, G1 and G280, we statistically subtract the field population and estimate metallicities using K-(J - K) color-magnitude diagrams (CMDs). Based on the slopes of their infrared giant branches we estimate [Fe/H] = −1.22 ± 0.43 dex for G1 and −0.15 ± 0.37 dex for G280. We combine our infrared observations of G1 with two epochs of optical HST-WFPC2 F-band data and identify at least one LPV based on color and variability. The location of G1's giant branch in the K, (V - K) CMD is very similar to that of M107, indicating a somewhat higher metallicity than our purely infrared CMD; [Fe/H]= −0.9 ± 0.2 dex.

We use B, V, and K-band images of the Antennae in a detailed analysis of its stellar populations. Significant large and small-scale spatial variations in the stellar populations are found by examining images pixel by pixel. Flux ratio, or linear color, diagrams allow us to find the stellar populations present in each pixel using a novel technique. This is done through a comparison of the colors of pixels to those of well-studied populations such as elliptical/S0 galaxies, Magellanic Cloud clusters, and Sc galactic nuclei, in addition to stellar population models. This technique allows us to study not only star clusters, but also the diffuse light present in the Antennae. From these flux-ratio diagrams, a luminosity-weighted de-reddened age image of the Antennae is constructed. Our analysis technique complements and extends results based on Hubble Space Telescope images.

We discuss new results based on RI and JHK photometry for 888 and 204 carbon stars, respectively, of the 1035 C stars found by Blanco and his collaborators in the Large Magellanic Cloud (LMC). Bolometric magnitudes and effective temperatures for these stars are calculated and compared with theoretical predictions. We find a spatial gradient in the transition luminosity between M and C type stars. This has implications for the age of the most recent major epoch of star formation in the LMC.

For a true picture of the stellar content of the bulges of spiral galaxies it is necessary to combine spectroscopic and photometric observations from the ultraviolet to the infrared. In early-type spirals one generally finds a metal-rich, old population with no excess of low mass stars. In later type systems there is an increasing contribution from young stars. The population in the Galactic bulge is representative and does not contain a significant number of stars with large IR excesses.

We present CCD imaging results of our sample of IRAS galaxies with spectral energy distributions peaking at 60μm (Vader et al 1988). The results support our suggestion that the activity in 60μm peaking galaxies is centrally concentrated, and represents an early stage of dust-embedded nuclear activity. This activity is probably triggered by a recent interaction/merger event as indicated by their peculiar optical morphologies. We propose that 60μm peakers are the precursors of S0’s in the case of amorphous systems, and ellipticals in the case of interacting galaxies.

Stars in Baade's Window at b = −4° are described. They are old, metal rich, and have a velocity dispersion greater than 100 km/sec. Their colors are unlike those of any other group of stars. Stars in other windows between b = −3 and −12° differ systematically from those in Baade's Window. The differences are best understood if they are caused by a metallicity gradient in the bulge. The distribution of surface brightness or surface density over the bulge has a much steeper falloff than that seen in other galaxies or in the very center of the Milky Way itself. It is now possible to link together stars in the immediate vicinity of the nucleus with those that are several hundred parsecs out. Understanding this linkage will help in understanding the history and evolution of stars throughout the bulge and that part of the inner disk with which it overlaps.

We are engaged in a long term study of the stellar component in the nuclear bulge of the Galaxy. Regions of low obscuration at different galactic latitudes above the galactic nucleus are surveyed for M giants with a transmission grating and thin prism at the prime focus of the CTIO 4-m reflector. Photographic and infrared photometry are obtained for samples of the stars found. Spectroscopic observations are used to investigate band strengths and radial velocities.

To understand the evolution of carbon and oxygen rich asymptotic giant branch (AGB) stars it is important to observationally establish the relations between parameters such as luminosity, age, and metallicity. The existence of luminous (brighter than the top of the first giant branch) AGB stars in clusters in the Magellanic Clouds (Mould and Aaronson 1979; Frogel, et al. 1980) provides a nearly ideal situation in which these relations can be determined. Although metallicities and main sequence turn-off ages are known for only a fraction of the clusters, the ranking scheme devised by Searle, et al. (1980; SWB) indicates that age and metallicity are closely related to one another.

This talk will briefly summarize some recent results based on infrared observations of giant stars in globular clusters. The program is being carried out jointly with Eric Persson and Judith Cohen of the Hale Observatories.