Rotation affects all the outputs of the evolution and nucleosynthesis of massive stars. We discuss the evolution of the rotational velocities, the internal ω-gradients, the tracks in the H-R diagram, the age determinations, the evolution of the surface N/C abundance ratios, the B/R number ratios of blue to red supergiants and the lifetimes in the WR stages.

We discuss which fraction of the matter flowing to the companion during a Roche lobe overflow phase can actually be accreted by the secondary star. Employing new evolutionary models for massive close binaries which include the effects of rotation for both components as well as angular momentum accretion and spin-orbit coupling, we propose a physical model to calculate the accretion efficiency in Case A and B systems. We provide examples showing that both cases, high and low accretion efficiency, do occur within these models, as it seems required by observed post-mass transfer systems. Furthermore, we discuss late evolutionary stages of such binaries, with emphasis on the formation of compact objects: what are their spin rates, which systems can produce black holes, which gamma-ray bursts?

A defining property of massive stars is the dominant, dynamical role played by radiation throughout the stellar interior, atmosphere, and wind. Associated with this radiation hydrodynamics are several distinct kinds of instabilities that can lead to convection in both core and envelope, clumping in atmosphere and wind outflow, and perhaps even the dramatic mass loss outbursts associated with Luminous Blue Variable phases. Here I review these instabilities with emphasis on basic physical properties of radiative driving. I draw on two specific examples of dynamical instability, namely the strong instability associated with line-driving of a stellar wind outflow, and the global stellar instabilities associated with approaching or exceeding a modified Eddington limit. I conclude with a brief mention of recent ideas on the role of stellar rotation in the shaping of bipolar LBV outbursts.

Stellar evolution sequences are presented for stars in the mass range 5-21 M⊙ with initial metallicity Z = 0.002 and initial helium abundance Y = 0.25 resembling average composition of the Small Magellanic Cloud. The stellar models are calculated with different treatment of convective mixing in regions of varying molecular weight gradient. The stellar sequences are used to study the morphology of the well-observed star cluster NGC 330 in the SMC. We argue that convective mixing should be inhibited in inhomogeneous stellar regions in order to understand the morphology of NGC 330. In other words, our contribution emphasizes the important role of semi-convection in the evolution of massive stars.

A wealth of recent observations confirms that the fast, dense winds of OB and Wolf-Rayet (WR) stars are highly structured, with the structures resulting from the inherently unstable nature of a radiatively-driven wind, as well as being triggered from the underlying photosphere. This review mainly addresses variability patterns observed in the winds and photospheric regions of presumably single stars. Schematically we divide the detectable structures into two broad categories: small-scale and large-scale inhomogeneities, with the former mainly of a stochastic behavior/origin, and the latter frequently demonstrating a recurrent, even periodic, behavior. We then discuss the nature and nurture of instabilities, highlighting phenomenological similarities and differences in the variability of OB and WR stars.

We discuss abundances for eight early B-type giant/supergiant stars in the SMC cluster NGC 330. All are nitrogen rich with an abundance approximately 1.3 dex higher than an SMC main-sequence field. Given the number of B-type stars with low rotational projected velocities in NGC 330 (all our targets have v sin i < 50 kms–1), we suggest that it is unlikely that the stars in our sample are seen almost pole-on, but rather that they are intrinsically slow rotators. Comparing these results with the predictions of stellar evolution models including the effects of rotationally induced mixing, we conclude that while the abundance patterns may indeed be reproduced, those models with initially large rotational velocities do not reproduce the observed range of effective temperatures of our sample, nor the currently observed rotational velocities. Binary models may be able to produce stars in the observed temperature range and provide a promising alternative to single star models for explaining the observations. We also discuss the clear need for stellar evolution calculations employing the correct chemical mix of carbon, nitrogen and oxygen for the SMC.

In this paper, I discuss the observational quantities that are useful for judging the successes and failures of current massive star evolutionary theory. The galaxies of the Local Group can serve as important laboratories for providing these diagnostics, as their metallicities vary by a factor of ten. We find that the evolutionary tracks do a good job of matching the distribution of stars in the H-R diagram during the main-sequence phase. However, none of the models produce RSGs that are as cool and as bright as what is observed. The relative number of WC and WN stars is a strong function of metallicity, and the Padova and Geneva ‘normal mass-loss’ models do a reasonably good job of matching the observations at low metallicities, but predict too few WCs at higher metallicity. The ‘enhanced’ mass-loss models of the Geneva group do not match the observations at all. New data is providing excellent statistics on the number of RSGs in these nearby galaxies, and the number ratio of RSGs to WRs is also an extremely sensitive function of metallicity. None of the models reproduce the trend of the RSG/WR ratio with metallicity.

Wind models of very massive stars with metallicities in a range from 10–4-1.0 Z⊙ are presented using a new treatment of radiation driven winds with depth dependent radiative force multipliers and a comprehensive list of more than two million of spectral lines in non-LTE. The models yield mass-loss rates, wind velocities, wind momenta and wind energies as a function of metallicity and can be used to discuss the influence of stellar winds on the evolution of very massive stars in the early universe and on the interstellar medium in the early phases of galaxy formation. It is shown that the normal scaling laws, which predict stellar mass-loss rates and wind momenta to decrease as a power law with metal abundance break down at a certain threshold. The new wind models are applied to calculate ionizing fluxes and observable UV-spectra of very massive stars as a function of metallicity using the wm-basic code developed by Pauldrach et al. (2001), and the efffects of metallicity are discussed.

We discuss the evolutionary properties of primordial massive and very massive stars, supposed to have formed from metal-free gas. Stellar models are presented over a large range of initial masses (8 M⊙ ≲ Mi ≲ 1000 M⊙), covering the hydrogen- and helium-burning phases up to the onset of carbon burning. In most cases the evolution is followed at constant mass. To estimate the possible effect of mass loss via stellar winds, recent analytic formalisms for the mass-loss rates are applied to the very massive models (Mi ≥ 120 M⊙).

We calculate a grid of star models with and without the effects of axial rotation for stars in the mass range between 2 and 60 M⊙ for the metallicity Z = 10–5. We find that in these models primary nitrogen is produced during the He-burning phase by rotational diffusion of 12C into the H-buraing shell. The intermediate mass stars of very low Z are the main producers of primary 14N, but massive stars also contribute to this production; no significant primary nitrogen is made in models at metallicity Z = 0.004 or above. We calculate the chemical yields in He, C, N, O and heavy elements and discuss the chemical evolution of the CNO elements at very low Z. Remarkably, the C/O vs. O/H diagram is mainly sensitive to the interval of stellar masses, while the N/O vs. O/H diagram is mainly sensitive to the average rotation of the stars contributing to the element synthesis.

Identifying the progenitors of Type Ib and Type Ic supernovae requires knowing, among other things, whether SNe Ib eject hydrogen, and whether SNe Ic eject helium, and perhaps even hydrogen. Recently it has become clear that some SNe Ib do eject hydrogen, and it may be that all SNe Ib do. Two arguments that have been made in the past that SNe Ic eject helium are difficult to confirm, but I discuss other possible evidence that SNe Ic eject helium, as well as hydrogen. If so, these elements extend to lower ejection velocities than in SNe Ib. The spectroscopic differences between SNe Ib and SNe Ic may depend on the radial distributions of the helium and hydrogen as well as on the ejected masses of helium and hydrogen. We should consider the possibility that SNe Ic are more mixed up.

Massive stars are born rotating rigidly with a significant fraction of critical rotation at the surface. Consequently, rotationally-induced circulation and instabilities lead to chemical mixing in regions that would otherwise be stable, as well as a redistribution of angular momentum. Differential rotation also winds up magnetic fields, causing instabilities that can power a dynamo and magnetic stresses that lead to additional angular momentum transport. We follow the evolution of typical massive stars, their structure and angular momentum distribution, from the zero-age main sequence until iron core collapse. Without the action of magnetic fields, the resulting angular momentum is sufficiently large to significantly affect the explosion mechanism and neutron star formation. Sub-millisecond pulsars result that could encounter the r-mode instability. In helium cores massive enough, at least at low metalicity, the angular momentum is also sufficiently great to form a centrifugally supported accretion disk around a central black hole, powering the engine of the ‘collapsar’ model for GRBs. Including current estimates of the effect of magnetic fields still allows the formation of rapidly rotating (~ 5-10 ms) pulsars, but might leave too little angular momentum for collapsars.

A small group of X-ray binaries currently provides the best evidence for the existence of stellar-mass black holes. These objects are interacting binary systems where the X-rays arise from accretion of material onto a compact object (i.e., an object with a radius of less than a few hundred km). In some favourable cases, optical studies of the companion star lead to dynamical mass estimates for both components. In 17 cases, the mass of the compact object in an X-ray binary has been shown to exceed the maximum mass of a stable neutron star (about 3 M⊙), which leads to the conclusion that these objects are black holes. In this contribution I will review the basic properties of these black hole binaries.

The final masses MCO,f for the CO-cores of WR stars with known masses are calculated taking into account mass-dependent mass loss of WR stars and clumping structure of the WR wind which allows the mass loss rate to be decreased by a factor of 3. The masses of MCO,f lie in the range (1-2) - (20-44)M⊙ and have continuous distribution in contrast with distribution of masses Mx of relativistic objects. The distribution of Mx seems to be bimodal with a gap in the range Mx = 2-4 M⊙. A mean CO-core mass <MCO,f = 7.4-10.3 M⊙ is close to that of black holes: <MBH = 8-10 M⊙. Difference between distributions of MCO,f and Mx allows us to suggest that the nature of a formed relativistic object (neutron star, black hole) is determined not only by the mass of a progenitor but also by some other parameters: rotation, magnetic field, etc.

The collapse of a massive star releases a considerable amount of gravitational potential energy. This energy is believed to be the power source of some of the largest explosions in the universe: supernovae, hypernovae, gamma-ray bursts. In this proceedings, we review the mechanisms by which the potential energy from stellar collapse can be tapped to produce these strong explosions, emphasizing how our understanding of massive stars can help constrain these mechanisms.

Core collapse supernovae (SN) are the final stages of stellar evolution in massive stars during which the central region collapses, forms a neutron star (NS), and the outer layers are ejected. Recent explosion scenarios assumed that the ejection is due to energy deposition by neutrinos into the envelope, but detailed models do not produce powerful explosions. There is new and mounting evidence for an asphericity and, in particular, for axial symmetry in several supernovae which may be hard to reconcile within the spherical picture. This evidence includes the observed high polarization and its variation with time, pulsar kicks, high velocity iron-group and intermediate-mass elements material observed in remnants, direct observations of the debris of SN 1987A, etc. Some of the new evidence is discussed in more detail. To be in agreement with the observations, any successful mechanism must invoke some sort of axial symmetry for the explosion. We consider jet-induced/dominated explosions of core collapse supernovae. Our study is based on detailed 3-d hydrodynamical and radiation transport models. We find that the observations can be explained by low velocity, massive jets which stall well within the SN envelope. Such outflows may be produced by MHD-mechanisms, convective dominated accretion disks on the central object or asymmetric neutrino emissions. Asymmetric density/chemical distributions and, for SN 2002ap, off-center energy depositions have been identified as crucial for the interpretation of the polarization.

We review the characteristics of nucleosynthesis in ‘hypernovae’, i.e., core-collapse supernovae with very large explosion energies (≳ 1052 ergs). The hypernova yields show the following characteristics: (i) the mass ratio between the complete and incomplete Si burning regions is larger in hypernovae than normal supernovae. As a result, higher energy explosions tend to produce larger [(Zn, Co, V)/Fe] and smaller [(Mn, Cr)/Fe], which could explain the trend observed in very metal-poor stars; (ii) because of enhanced α-rich freeze-out, 44Ca, 48Ti, and 64Zn are produced more abundantly than in normal supernovae. The large [(Ti, Zn)/Fe] ratios observed in very metal poor stars strongly suggest a significant contribution of hypernovae; and (iii) oxygen burning takes place in more extended regions in hypernovae to synthesize a larger amount of Si, S, Ar, and Ca (‘Si’), which makes the ‘Si’/O ratio larger. The abundance pattern of the starburst galaxy M 82 may be attributed to hypernova explosions. We thus suggest that hypernovae make important contribution to the early Galactic (and cosmic) chemical evolution.

It is shown that up to 90% of the known WR+O binaries have been formed as a result of the mass transfer in O+O binary systems.

We derive a constraint on direct black hole formation from the evolution of [O/Fe] as function of time, during the early evolution of the Galaxy in the solar neighbourhood. Since oxygen is dominantly produced by massive stars, the evolution of [O/Fe] is an indirect observable signature of the death of massive stars. We use a detailed Galactic code that computes as function of time the chemical composition of the interstellar gas, out of which successive generations of stars are formed. From our simulations we conclude, that to fit simultaneously the observed [O/Fe] evolution and other observational constraints: (i) all massive stars (single or binary) with M > 40 M⊙ should form massive black holes with the ejection of at least 7 M⊙ of oxygen and little carbon and iron; and (ii) mass loss by stellar wind during the Luminous Blue Variable phase and/or helium burning phase is likely to be metallicity dependent.

We perform radiation hydrodynamics simulations of mass transfer in close and massive binary systems, focusing especially on the impact of radiation pressure and wind momentum from the two luminous stars that compose the system. We find that for the large mass transfer rates important for the evolution of such binary systems (of the order of 10–3 M⊙ yr–1), the light and wind momenta are too low to affect the behaviour of the dense gas stream ejected by the Roche Lobe filling component. In particular, the presence of a wind-wind collision between the two stars has no effect on the gas stream dynamics.