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About a quarter of massive binary stars undergo mass transfer while both stars burn hydrogen at their cores, first on the thermal and then on the nuclear timescale. The nuclear timescale mass transfer leads to observable counterparts: the…
The evolution of massive stars in general, massive close binaries in particular depend on processes where, despite many efforts, the physics are still uncertain. Here we discuss the effects of stellar wind as function of metallicity during…
Models of rotationally-driven dynamos in stellar radiative zones have suggested that magnetohydrodynamic transport of angular momentum and chemical composition can dominate over the otherwise purely hydrodynamic processes. A proper…
Massive WR stars are evolved massive stars characterized by strong mass-loss. Hypothetically, they can form either as single stars or as mass donors in close binaries. About 40% of the known WR stars are confirmed binaries, raising the…
Massive stars play a major role not only in stellar evolution but also galactic evolution theory. This is because of their dynamical interaction with binary companions, and because their strong winds and explosive deaths as supernovae…
The recent finding by Chevalier & Ilovaisky (1998) that OB-supergiant X-ray binaries have relatively large runaway velocities whereas Be/X-ray binaries have low runaway velocities, provides confirmation of the current models for the…
A large population of fragile, wide (> 1000 AU) binary systems exists in the Galactic field and halo. These wide binary stars cannot be primordial because of the high stellar density in star forming regions, while formation by capture in…
Be stars make up almost 20% of the B star population, and are rapidly rotating stars surrounded by a disc; however the origin of this rotation remains unclear. Mass transfer within close binaries provides the leading hypothesis, with…
We present the results of optical spectroscopic follow-up of 125 candidate main sequence OB stars in the Small Magellanic Cloud (SMC) that were originally identified in the S3MC infrared imaging survey as showing an excess of emission at 24…
In massive stars, magnetic fields are thought to confine the outflowing radiatively-driven wind, resulting in X-ray emission that is harder, more variable and more efficient than that produced by instability-generated shocks in non-magnetic…
We examine self-consistent parameterizations of the high-mass stellar population and resulting feedback, including mechanical, radiative, and chemical feedback, as we understand them locally. To date, it appears that the massive star…
Stellar mergers are responsible for a large variety of astrophysical phenomena. They form blue straggler stars, give rise to spectacular transients, and produce some of the most massive stars in the Universe. Here, we focus on mergers from…
I present the results of radiation-driven mass-loss predictions for hot stars of all mass. Mass loss is an important aspect for the evolution of massive stars, the rotational properties of the progenitors of gamma-ray bursts, and is…
Considering the physics of radiation-driven winds of massive stars, the wind properties should depend on the metal content of the stellar atmosphere. Therefore, studying the winds of massive stars in different metallicities provides a…
The orientation of a massive binary undergoes a random walk due to gravitational encounters with field stars. The rotational diffusion coefficient for a circular-orbit binary is derived via scattering experiments. The binary is shown to…
Mass loss is a key physical process in the evolution of massive stars, the impact of which propagates into galactic evolution, population synthesis models, the interpretation of high-redshift galaxies, and explosive events such as…
We present evolutionary pathways for creating hot subdwarf OB (sdOB) stars from hierarchical triple configurations. We use the population synthesis code Multiple Stellar Evolution (MSE) to follow the stellar, binary, and gravitational…
Mass loss bridges the gap between massive stars and supernovae (SNe) in two major ways: (i) theoretically it is the amount of mass lost that determines the mass of the star prior to explosion, and (ii) observations of the circumstellar…
The proximity & low dust extinction of the Magellanic Clouds provides an ideal environment for metal-poor massive stars to be studied in detail. The HST ULLYSES initiative has provided exquisite ultraviolet spectroscopy of a large sample of…
Surveys of the binary populations in the solar neighbourhood have shown that the periods of G- and M-type stars are log-normally distributed. However, observations of young binary populations suggest a log-uniform distribution. Clearly some…