We have developed a new version of the SD model for type Ia supernovae (SNe Ia) in which a common envelope (CE) is assumed to form if the mass-transfer rate between a carbon/oxygen white dwarf (CO WD) and its companion exceeds a critical accretion rate. Based on this model, we found that both SN 2002cx-like and SN Ia-CSM objects may share a similar origin, i.e. these peculiar objects may originate from the explosion of hybrid carbon/oxygen/neon white dwarfs (CONe WDs) in SD systems, where SNe Ia-CSM explode in systems with a massive CE of ∼1 M⊙, while SN 2002cx-like events correspond to events without a massive CE.

Strong winds from massive stars are a topic of interest to a wide range of astrophysical fields. In High-Mass X-ray Binaries the presence of an accreting compact object on the one side allows to infer wind parameters from studies of the varying properties of the emitted X-rays; but on the other side the accretor’s gravity and ionizing radiation can strongly influence the wind flow. Based on a collaborative effort of astronomers both from the stellar wind and the X-ray community, this presentation attempts to review our current state of knowledge and indicate avenues for future progress.

Smoothed particle hydrodynamics (SPH) models of the recurrent nova RS Ophiuchi are presented, along with simple models for circumstellar absorption lines. The evolution of the model sodium line is similar to the behaviour in some Type Ia SNe, e.g. SN2006X.

Here we review how binary interactions affect the final pre-supernova structure of massive stars and the resulting supernova explosions. (1) Binary-induced mass loss and mass accretion determine the final envelope structure, the mass, radius and chemical composition, which are mainly responsible for the supernova appearance and supernova (sub-)type. (2) Mass loss can also drastically change the core evolution and hence the final fate of a star; specifically, around 10 M⊙, it determines whether a star explodes in a supernova or forms a white dwarf, while for larger masses it can dramatically increase the minimum main-sequence mass above which a star is expected to collapse to a black hole. (3) Mass loss before the supernova directly affects the circumstellar medium (CSM) which can affect the supernova spectrum (e.g. account for the IIn phenomenon), produce powerful radio emission and, in extreme cases, lead to a strong interaction with the supernova ejecta and thus strongly modify the lightcurve shape; it may even be responsible for some of the superluminous supernovae that have recently been discovered.

As has been shown previously, the triple-ring nebula around SN 1987A can be understood as a direct consequence of the merger of two stars, some 20,000 yr before the explosion. Here we present new SPH simulations that also include the pre-merger mass loss and show that this may be able to explain other structures observed around SN 1987A, such as Napoleon's hat and various light echoes.

Among the possible progenitor scenarios considered for Type Ia supernovae, those that involve a carbon–oxygen white dwarf (CO WD) accreting stably towards the Chandrasekhar mass should undergo a phase of hydrostatic carbon burning under high densities and strong convection: the simmering or carbon–flash phase, which can extend for a few hundred years before explosion. During this phase the progenitor CO WD can burn a small fraction of its carbon hydrostatically, releasing energy and ashes that make the star convective and able to capture electrons from the degenerate plasma. In this work we present simplified pre–supernova evolution models of CO WDs growing towards the Chandrasekhar mass accreting matter stably and evolving through the simmering phase towards ignition in order to explore the effects of different initial masses and cooling times in the final chemical composition of the WD before explosion. Preliminary results show that, as expected, denser systems at the start of the simmering phase undergo stronger neutronization. The amount of neutronization is less than what is found in the one–zone models of Chamulak et al. (2008), about a third, and can vary by about a factor of two depending on the exact path to explosion.

The Supernova Working Group was re-established at the IAU XXV General Assembly in Sydney, 21 July 2003, sponsored by Commissions 28 (Galaxies) and 47 (Cosmology). Here we report on some of its activities since 2005.

Using binary population synthesis (BPS), we studied the birthrates of SNe Ia for two progenitor models – the single degenerate model and the double degenerate model. We find that the birthrates from both models are within a factor of a few comparable to those inferred observationally. For each model, we investigate different star-formation histories (single star burst or constant star formation), different metallicities (Z = 0.02, 0.004, 0.001), different parameters for the BPS model (mass transfer efficiency during stable mass transfer, common-envelope ejection parameters) and obtain the evolution of birthrates with time.

Using Eggleton’s code, we performed a series of binary evolution calculations in order to investigate the criterion for dynamical instability of mass transfer in binaries. In these calculations, we took the donor’s mass on the zero-age main sequence (ZAMS) from 0.8 to 1.9 M⊙. For each mass, we systematically varied the mass of the core at the beginning of mass transfer and the mass of the companion star. We assumed that mass transfer was completely non-conservative and that all the mass that was lost from the system carried with it the orbital angular momentum of the accreting component. We found that the critical mass ratio, above which mass transfer is dynamically unstable, is from 1.1 to 1.3 in these red-giant binary systems.

Irradiation of the secondaries in close binary systems affects their appearance and can drastically change their internal structure and hence long-term evolution. In this paper we review the main effects of external irradiation in close binaries with compact primaries, such as the distortion of the shape of the secondary and the conditions for the occurrence of outer critical configurations, and apply these to normal X-ray binaries, including systems such as HZ Her/Her X-l, Vela X-l and black-hole binaries during outburst (e.g. Nova Sco). Particular emphasis will be given to the role of circulation driven by the external heating and the radiative surface stress. We have developed a three-dimensional fluid dynamics code for modelling these effects. We present initial results of self-consistent calculations for the circulation in irradiated systems and show how the inclusion of these effects is vital to the understanding and interpretation of any system where external irradiation of the secondary is significant.

We performed full binary evolution calculations and carried out binary population synthesis studies in order to investigate the formation of subdwarf B (sdB) stars via the channels of stable Roche lobe overflow (RLOF), common envelope ejection and helium white dwarf mergers. Our model is successful in the explanation of observational properties of sdB stars, e.g. we explained the orbital period – minimum companion mass (log P – Mcomp) diagram, the effective temperature – surface gravity (Teff – log g) diagram, the orbital period distribution, the log(gθ4) (θ = 5040/Teff) distribution, the mass function distribution, the binary fraction of sdB stars, the fraction of sdB binaries with WD companions, the birth rates, the space number densities, etc. We conclude that (a) the first RLOF needs to be more stabilized than commonly assumed, (b) the first stable RLOF is not conservative, (c) common envelope ejection is very efficient.

Thorne-Żytkow objects (TŻOs) are red supergiants with neutron cores. The energy source in TŻOs with low-mass envelopes (≲8 M⊙) is accretion onto the neutron core, while for TŻOs with massive envelopes (≲14 M⊙) it is nuclear burning via the exotic rp process. TŻOs are expected to form as a result of unstable mass transfer in high-mass X-ray binaries, the direct collision of a neutron star with a massive companion after a supernova or the collision of a neutron star with a low-mass star in a globular cluster. We estimate a birth rate of massive TŻOs in the Galaxy of ∼2 10−4 yr−1. Thus, for a characteristic TŻO lifetime of 105–106 yr there should be 20–200 TŻOs in the Galaxy at present. These can be distinguished from ordinary red supergiants because of anomalously high surface abundances of lithium and rp-process elements, produced in the TŻO interior. The TŻO phase ends when either the star has exhausted its rp-process seed elements or the envelope mass decreases below a critical mass (∼14 M⊙). Then nuclear burning becomes inefficient and a neutrino runaway ensues, leading to the dynamical accretion of matter near the core onto the neutron star and its spin up to spin frequencies of up to ∼100 Hz. The fate of the massive envelope is not entirely clear. If a significant fraction can be accreted onto the core, the formation of a black hole becomes likely. Part of the envelope may collapse into a massive disk which may ultimately become gravitationally unstable and lead to the formation of planets or even low-mass stars. We discuss the various possible outcomes and suggest a possible link between massive TŻOs and soft X-ray transients.

External irradiation can completely alter the internal structure of the secondary in a low-mass X-ray binary (LMXB). For radiation fluxes as are typically found in LMXBs, the secondary expands by a factor of 2 to 3 in order to relax towards a new state of thermal equilibrium. This relaxation process provides a new mass-transfer driving mechanism for LMXBs, which can drastically alter the evolution of these systems.