I present measurements of the projected rotational velocities of a sample of 100 early B-type main-sequence stars in the Large Magellanic Cloud (LMC). This is the first extragalactic study of the distribution of stellar rotational velocities. The sample is drawn from two sources: from the vicinity of the main-sequence turnoff of young clusters (ages 1–3 × 107 yr) and from the general field. I find that the cluster population exhibits significantly more rapid rotation than that seen in the field. I have drawn analogous Galactic cluster and field samples from the literature. Comparison of these samples reveals the same effect. I propose that the observed difference between cluster and field populations can be explained by a scenario of evolutionary enhancement of the surface angular momentum over the main-sequence lifetime. A comparison is made between the cluster and field populations of the LMC and the Galaxy in order to explore the effects of metallicity. This shows that the stars of the LMC are more rapid rotators than their Galactic counterparts.

This study presents a tomographic survey of a subset of the outer halo (10–40 kpc) drawn from the Sloan Digital Sky Survey Data Release 6. Halo substructure on spatial scales of >3 degrees is revealed as an excess in the local density of sub-giant stars. With an appropriate assumption of a model stellar isochrone it is possible for us to then derive distances to the sub-giant population. We describe three new candidate halo substructures; the 160- and 180-degree over-densities (at distances of 17 and 19 kpc respectively and radii of 1.3 and 1.5 kpc respectively) and an extended feature at 28 kpc that covers at least 162 deg2, the Virgo Equatorial Stream. In addition, we recover the Sagittarius dwarf galaxy (Sgr) leading-arm material and the Virgo Over-Density.

The derived distances, together with the number of sub-giant stars associated with each substructure, enables us to derive the integrated luminosity for the features. The tenuous, low surface brightness of the features strongly suggests an origin from the tidal disruption of an accreted galaxy or galaxies. Given the dominance of the tidal debris of Sgr in this region of the sky we investigate if our observations can be accommodated by tidal disruption models for Sgr. The clear discordance between observations and model predictions for known Sgr features means it is difficult to tell unambiguously if the new substructures are related to Sgr or not. Radial velocities in the stellar over-densities will be critical in establishing their origins.

We present the results of our studies of Be stars within the Magellanic Clouds. We have studied the Be population within four young populous clusters, NGC 330 in the SMC, NGC 1818, 2004 and 2100 in the LMC as well as the field population around NGC 2004. The Be fraction within each cluster is seen to peak towards the luminosity of the main sequence turnoff. The field, which exhibits a large spread of ages, has a Be fraction more uniformly distributed in luminosity. We interpret this difference as evidence for an evolutionary enhancement of the Be phenomenon that occurs towards the end of the main sequence lifetime.

We present new UV, visual and Hα photometry obtained with the WFPC2 of NGC 330, NGC 1818, NGC 2004 and NGC 2100, four young populous clusters in the MCs. We present observational evidence for a degree of convective core overshoot in excess of that currently applied in standard models.