We summarize the properties of tidal dwarf candidates in a sample of interacting galaxies and classify objects in tidal tails depending on their morphological appearance. New high-resolution dynamical models are needed to understand how the different structures seen in tidal tails are formed.

This review focuses on how galaxies and their globular cluster systems form. I first discuss the now fairly convincing evidence that some globular clusters form in galaxy starbursts/mergers. One way these observations are valuable is they place important constraints on the physics of the formation of globular clusters. Moreover, it is natural to associate the typically metal-rich clusters forming in mergers with the substantial metal-rich population of globulars around ellipticals, thereby implying an important role for galaxy mergers in the evolution of elliptical galaxies. I also highlight some new observational efforts aimed at constraining how and when elliptical galaxies and their globular cluster systems formed. These include systematic studies of the number of globular clusters around galaxies as a function of morphological type, studies of the kinematics of globular cluster populations in elliptical galaxies, and a variety of observational programs aimed at constraining the relative ages of globular clusters within galaxies as a function of cluster metallicity. The understanding of the formation of globular cluster systems and their host galaxies has grown dramatically in recent years, and the future looks equally promising.

We study the evolution of the main properties of globular cluster systems in elliptical galaxies. In particular, we focus our attention on the evolution of the mass function of globular cluster systems (GCMF), on the fraction of surviving clusters and on the ratio of the final to initial total mass in clusters and we explore the dependence of these properties on the structure of the host galaxy and on the initial GCMF. We show that the observed universality of the GCMF parameters in galaxies with different structures can be reconciled with the effects of evolutionary processes and with the significant differences in the efficiency of evolutionary processes in different host galaxies; the final mean masses of globular cluster systems in massive galaxies can be very similar to each other with a small galaxy-to-galaxy dispersion in spite of large differences in the fraction of surviving clusters.

The gravitational instability of expanding shells is discussed. Linear and nonlinear terms are included in an analytical solution in the static and homogeneous medium. We discuss the interaction of modes and give the time needed for fragmentation. Masses of individual fragments are also estimated and their formation rates and the initial mass function are derived. Results of simulations are compared to observation.

The formation of massive stellar clusters in turbulent molecular clouds is investigated. We include artificial star formation and energy feedback of newly born stars. The obtained systems are not likely to survive. Case studies to determine conditions necessary for forming bound clusters will be done in the future.

The formation of globular clusters is still an unsolved problem. Though most scenarios assume a massive molecular cloud as the progenitor, it is unclear how the cloud is transformed into a star cluster. Here a scheme of supernova (SN) induced cluster formation is investigated. In this scenario the expanding SN shell accumulates the mass of the cloud. This is accompanied by fragmentation resulting in star formation in the shell. If this stellar shell expands sufficiently slowly, its self-gravity leads to a recollapsing shell, thus forming one or several stellar clusters.

In this paper N-body simulations of collapsing shells moving on circular orbits in a galactic potential are presented. It is shown that typical shells (105 M⊙, 30 pc) evolve to twin clusters in the galactocentric distance range between 3 and 11 kpc. Their masses show a strong radial trend: on orbits inside 5 kpc both clusters have almost equal mass. Outside 5 kpc the more massive twin cluster contains about 55% of the shell's mass, whereas the mass of the smaller decreases linearily to 15% at 11 kpc. Outside 11 kpc the collapsing shells end up in a single cluster. Inside 3 kpc the shells are tidally disrupted and only fragments substantially less massive than the initial shell survive.

A CO survey of the LMC has been completed in the J = 1−0 carbon monoxide emission at 2.6 mm wavelength with NANTEN. This survey has revealed the first complete sample of giant molecular clouds (GMCs) in the LMC at a linear resolution of ∼ 40 pc. The GMCs exhibit a good spatial correlation with youngest stellar clusters often associated with the giant H II regions. The ages of clusters associated with GMCs are fairly young, ≲ 10 Myr, demonstrating that cluster formation is ongoing in these GMCs. In addition, compact groups of the young clusters are often found at the peak position of the GMCs, e.g., N159 and N44, while much looser groups are away from the GMCs. This suggests that the clusters are formed in groups and are dispersed as they become old.

We present a new study of the low end of the stellar IMF of NGC 330, the richest young star cluster in the Small Magellanic Cloud (SMC). Using deep broadband images taken with the HST/WFPC2 we have derived the cluster's luminosity function and constructed the initial mass function (IMF) in the mass range 1 − 7M⊙. We have investigated the IMF as a function of the radial distance from the cluster center. We find that, after correction for background contamination, the IMF is fairly homogeneous with a slope slightly steeper than Salpeter's in the central regions of the cluster (< 40″) but becomes increasingly steeper with distance, indicating a preponderance of massive stars in the core of the cluster. NGC 330 is one of the first clusters for which evidence of mass segregation is directly found.

We present a five-field, six-color WFPC2 mosaic of 30 Doradus which constitutes the most detailed ever optical image of a starburst region. With the aid of NICMOS, STIS, and CO data we discuss the most recent star formation history in the region and its relationship with the original and present structure of the parent molecular cloud.

We present the observational signature of a statistically significant number of very massive stars around the core of R136 and discuss the evidence for dynamical processes to be responsible for their apparent location. Alternative scenarios are discussed as well.

We have searched the WFPC2/HST archive for data on nearby massive young clusters with low extinction and we have analyzed 27 such objects. A clear dichotomy between objects with a compact core and without it is observed. We attribute this bimodality to the initial conditions of the parent giant molecular clouds and we discuss its implication towards the long-term evolution of the clusters.

Using new (Cycle 9) HST / WFPC2 data, we have studied a peculiar star forming region in the nearby Sc-type spiral NGC 6946. The region has a bubble-like shape and a diameter of about 600 pc. Near the centre is an extremely luminous young globular cluster with MV = −13.2 mag. The cluster has a compact core with a core radius of about 1.3 pc but is surrounded by an extended halo with a power-law luminosity profile similar to that observed for young LMC clusters. From Keck / HIRES high-dispersion spectroscopy we measure a velocity dispersion of 10 km s−1, leading to a dynamical mass estimate of about 1.7 × 106 solar masses. The dynamical mass estimate is comparable to the expectation from population synthesis modelling under the assumption of a Salpeter IMF extending down to 0.1 M⊙.

If the cluster formation rate is constant and the disruption time of clusters depends only on their initial mass as tdis = t4 × (Mcl/104M⊙)γ, the values of t4 and γ can be derived in a very simple way from the age and mass histograms of observed clusters. We derived these values from cluster samples in fields of five galaxies: M51, M33, LMC, SMC and the solar neighbourhood. The values of γ are the same in the five galaxies with < γ > = 0.62 ± 0.03. However the disruption time t4 of clusters of 104M⊙ is very different in the different locations.

I describe preliminary results from an I-band snapshot survey with HST/WFPC2 of nuclear star clusters in late-type spiral galaxies. The goal of the program is to derive the fraction of galaxies that harbor a nuclear star cluster, and to analyse their photometric and structural properties. Together with follow-up spectroscopy, the survey will illuminate the formation mechanism of nuclear star clusters and the implications for the dynamical and morphological evolution of the host galaxy.

The first results of a study of the circumnuclear star-forming regions in HST broad band images of the nearby galaxy NGC4314 are presented. After modeling the bulge stellar population using ellipse fitting and subtracting the resulting model from the original images, aperture photometry of the individual star-forming regions in the ring was performed. For a total of 75 regions detected 3σ above the background, we obtained mean colors (f439—f569) = −0.72 ± 0.27, and (f569—f814) = −0.69 ± 0.35, with the NW regions being ∼ 0.5 mag bluer in both colors than the NE ones, an effect that may be caused by internal reddening.

New theoretical isochrones are presented and compared to the observational data.

We present new deep VLT color-magnitude diagrams of three intermediate-age populous star clusters in the LMC. These data will be used independently by the Padova and Yale stellar evolution Groups to address issues relevant to the evolution of intermediate-mass stars: mainly the extent of the core convective overshoot, as well as other poorly determined parameters, such as mass loss during stellar evolution, internal rotation, and He content.

We present a statistical approach for determining the age of Globular Clusters (GCs) that allows estimating the age derived from CMDs more accurately than the conventional method of isochrone fitting. We measure how closely a set of synthetic CMDs constructed from different evolutionary models resemble the observed ones by determining the likelihood using Saha and χ2 statistics. The model which best matches the observational data, of a set of plausible ones, is the one with the highest value of the estimator. We apply this method to a set of three different evolutionary models presented by three different authors. Each of these sets consists again of many different models of various chemical abundances, ages, input physics and the like. We subsequently derive the age of GCs NGC 6397, M92 and M3. With a confidence level of 99%, we find that the best estimate of the age is 14.0 Gyrs within the range of 13.8 to 14.4 Gyrs for NGC 6397, 14.75 Gyrs within the range of 14.50 to 15.40 Gyrs for M92, and 16.0 Gyrs within the range of 15.9 to 16.3 Gyrs for M3.

I propose and apply a method for deriving ages of the metal-poor globular clusters (GCs) in a distance-independent way, which is based on an age indicator related to the main sequence in the two-color diagrams using the U-B index. The age of the metal-poor GC NGC 6397 has been estimated, using Yale isochrones of Demarque et al. (1996), to be close to 16 Gyr provided the cluster metallicity is near [Fe/H] = −2.0.

For the first time, we have taken into account the detailed systematic variation of horizontal-branch (HB) morphology with age and metallicity in our population synthesis models and they result that the integrated Hβ index is significantly affected by the presence of blue HB stars. As a matter of fact, due to the systematic HB morphology variation, it is found that Hβ does not monotonically decrease as metallicity increases at given ages, but shows a kind of wavy feature. According to our models, a systematic difference between the globular cluster system in the Milky Way Galaxy and that in NGC 1399 in the Hβ vs. Mg2 plane is explained if globular cluster systems in giant elliptical galaxies are a couple of billion years older, in the mean, than the Galactic counterpart.