We review properties of the most metal-deficient globular clusters and halo stars in the local universe as of March 2001, with goals of examining present evidence for the duration of the initial burst of massive cluster formation in the Milky Way, determining when that burst occurred, and elucidating what appears to be limiting our present understanding. Such issues bear upon many topics to arise later in the Symposium.

The properties of the globular clusters located within 20° × 20° of the Galactic Center are discussed. In particular their spatial distribution, metallicities and ages are presented and discussed in the context of different scenarios of bulge formation.

Technology is now allowing for the investigation of star clusters outside of the Milky Way. As attention turns to the extragalactic star clusters, a perception that the system of star clusters in the Milky Way is well understood may grow, resulting in the neglect of these important objects. In this review, the status of our understanding of the Milky Way's open star cluster population will be discussed. Specifically, I will attempt to illustrate not only the important information that can and must be learned from these nearby star clusters, but also the degree to which our understanding of the Galactic open clusters remains incomplete.

This review presents the current status of our knowledge of M31 star clusters. Given the broadness of the subject, I chose to focus on some of its aspects which are not covered by the other participants in this conference.

We present a progress report of our wide field CCD survey of globular clusters in M31. We have covered a 3 deg × 3 deg area centered on M31, using the KPNO 0.9m and Washington CMT1 filters. Our survey is much deeper and more sensitive than previous surveys. We have found several hundred new globular cluster candidates in M31 in addition to confirming previously known globular clusters, and also have found a number of interlopers among previous globular cluster catalogs. We have also obtained spectra of about 500 objects among these candidates using HYDRA at the WIYN 3.5m telescope, which are used for classification and measuring the radial velocity of the candidate objects. When completed, a new master catalog of globular clusters in M31 will be made, combining the new globular clusters with the known globular clusters.

With the ultimate goal of distinguishing between various models describing the formation of galaxy halos (e.g., radial collapse, chaotic mergers), we present the results of a spectroscopic study of the globular cluster system of M31. We have obtained deep, intermediate-resolution spectra for several hundred of the M31 globular clusters using the WYFFOS fibre-fed spectrograph at the William Herschel Telescope. These observations have yielded precise radial velocities and metallicities for over 200 members of the M31 globular cluster population, the vast majority of which represent new data or significant improvements over pre-existing data.

Globular cluster ages are more than just lower limits to the age of the universe; the distribution of ages constraints the timescales for galaxy formation and chemical evolution. Globular cluster populations with different metallicities have now been detected in many galaxies, and understanding how these populations formed requires knowing their relative ages. We examined the relative ages of the two M31 globular cluster populations using their color and luminosity distributions and found that the metal-rich clusters could be up to 50% younger than the metal-poor clusters. While a small delay in the formation of metal-rich clusters might be imposed by chemical enrichment timescales, a large age gap demands a more detailed explanation. I outline several possibilities and their promises and problems.

The power of HST to resolve dense stellar aggregates is such that most of the relevant information on the stellar populations of Fornax was obtained only recently. These results are presented here both for the globular clusters and for the field. But Fornax has probably been the most often studied dSph galaxy, partly on account of its abundant system of globular clusters. A brief retrospective is presented, not only for its historical interest but also because it reveals the striking improvement in observational tools and analysis techniques that has taken place over the last twenty years.

The Milky Way globular cluster system serves as a reference for the study of more distant galaxies. Here I stress that there are still things we do not know about the globular cluster system of our own galaxy: their total number, their spatial motions and distances, and their IR properties. If our best reference point is not fully known, caution should be exercised when interpreting observations of distant systems. At the same time, when studying distant ellipticals it is not always advisable to rely on the Milky Way as a comparison. For example, only recently the first full calibration of the luminosity function of the globular cluster system of an elliptical galaxy was made, necessary to compare apples with apples.

The ‘Second Parameter Effect’ (2ndPE) has long been recognized as an important probe into the formation of spiral galaxies. The concept that the horizontal branch morphologies of globular clusters are primarily affected by metal abundance in the inner halo (RGC<8 kpc) of the Galaxy but require an additional parameter (probably cluster age) to explain their behavior in the outer halo (RGC > 8 kpc), suggests that the former experienced a rapid monotonic collapse while the latter underwent a slower chaotic formation scenario. As such, in the Milky Way, the so-called second parameter boundary is located at 8 kpc. We find that, in the other Local Group spirals — M31 and M33 — this boundary lies at ∼40 kpc and ∼0 kpc, respectively. We therefore speculate that the boundary delimiting rapid monotonic halo collapse from the chaotic accretion of dwarf galaxy fragments is inversely related to the mass of the spiral galaxy.

The characteristics of the cluster systems of the Magellanic Clouds, as inferred from integrated properties, are compared with those from individual cluster studies and from the field population. The agreement is generally satisfactory though in the case of the LMC, the lack of clusters older than ∼3 Gyr is not reflected in the field population. The possible origin(s) for this cluster “age-gap” are discussed. The SMC cluster age-metallicity relation is also presented and discussed.

I summarize our knowledge of star clusters and associations in irregular galaxies other than the Magellanic Clouds in the Local Group. Surveys affording complete area coverage at high angular resolution are still lacking. Confirmed globular clusters are known only in NGC 6822 and WLM. Very few dIrrs contain populous or sparse open clusters. There is a pronounced deficiency of intermediate-age and young clusters. Apart from parent galaxy mass, the lack of interactions may be a key reason for the lack of cluster formation in the dIrrs. All dIrrs have one or several short-lived OB associations in the star-forming regions in their centers.

We present a preliminary report on the first deep near infrared photometry of 2MASS GC 01 and 2MASS GC 02 - new Galactic globular cluster candidates, discovered by the 2MASS. The red giant branch slopes yielded [Fe/H]=-0.42 ± 0.15 dex and [Fe/H]=-0.66 ± 0.17 dex, respectively for GC 01 and GC 02. We estimated the reddening towards GC 01 and GC 02: E(B - V) = 5.36 ± 0.20, and E(B - V) = 4.55 ± 0.17. The calculated distance moduli to the clusters are: (m - M)0 = 13.53 ± 0.27 and (m - M)0 = 14.53 ± 0.31 for GC 01 and GC 02. Our best fit for the radial surface brightness profile of GC 02 yields: lg(rc) = 1.40, lg(rh) = 1.54, lg(rt) = 1.31, and c=1.60. CC 01 is less concentrated: lg(rc) = 1.63, lg(rh) = 1.7, lg(rt) = 1.25, and c=1.41.

We present our recent revision of model constructions for the horizontal-branch (HB) morphology of globular clusters, which suggests the HB morphology is more sensitive to age compared to our earlier models. We also present our high precision CCD photometry for the classic second parameter pair M3 and M13. The relative age dating based on this photometry indicates that M13 is indeed older than M3 by 1.7 Gyr. This is consistent with the age difference predicted from our new models, which provides a further support that the HB morphology is a reliable age indicator in most population II stellar systems.

We study the globular clusters M3 and Palomar 3 as a “second parameter (2ndP) pair,” showing that: i) M3 has a surprisingly strong internal 2ndP; ii) The dispersion in mass on the Pal 3 horizontal branch (HB) is intrinsically very small, leading to the most apparent differences in HB morphology between M3 and Pal 3; iii) Ignoring the difference in HB mass dispersion between M3 and Pal 3, their relative HB types can be accounted for by a fairly small difference in age, of order 0.5–1 Gyr.

We derive the age difference between NGC 288 and NGC 362 using the bimodal horizontal branch (HB) of NGC 1851 as a “bridge” in the CMD analysis. Our results suggest that NGC 288 is older than both NGC 362 and NGC 1851 by ⋍ 2 ± 1 Gyr. A new grid of synthetic HBs discloses that age may be the second parameter (2ndP) for this pair provided that the Carretta & Gratton (1997) metallicity scale is to be preferred over the Zinn & West (1984) scale. In addition, the dispersion in ZAHB mass is found to be about twice as large in NGC 362 as in NGC 288, probably due to the much higher central density of the former.

Positions and absolute proper motions of 264 stars in the field of about 70′ × 70′ around the globular cluster M13 were determined. In the astrometric reduction, three early and three late epoch plates taken with the 40cm refractor at Shensan, Shanghai, China, were used, with the time baseline of 73 years. The reduction was done using the central overlapping algorithm, with 5 Hipparcos stars and 38 Tycho-2 stars used as reference stars. Based on the reduced proper motion data, the membership probabilities of the sample stars were determined. An absolute proper motion of the cluster of 1.49 ± 0.36 mas yr−1 in right ascension and 3.06±0.35 mas yr−1 in declination was obtained. From this proper motion, together with distance and radial velocity data, we derived the space motion of M13 and via numerical integration also the orbit of the cluster in the Galaxy.