Employing Eggleton’s stellar evolution code, we carry out 150 runs of non-conservative Population I binary evolution calculations with the initial primary mass between 1 and 8 M⊙, the initial mass ratio q = M1/M2 between 1.1 and 4 and the onset of Roche lobe overflow (RLOF) at the early, middle or late Hertzsprung gap. We assume that 50 per cent of the mass lost from the primary during the RLOF is accreted on to the secondary, the other 50 per cent is lost from the system, carrying away the same specific angular momentum as the centre of mass of the primary. We find that the remnant mass depends on when the RLOF begins in the Hertzsprung-gap and the dependency increases with the primary mass. The remnant mass, however, does not depend much on the initial mass ratio, as compared to conservative cases. For qi = 1.1, we fit a formula for the remnant mass as a function of the initial mass M1i of the primary and the radius of the primary at the onset of RLOF with an error less than 2.61 per cent.

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.

We present the results of photometric and high-resolution spectroscopic studies of a group of B[e] stars (Be stars with warm dust or B[e]Ds) and of two cooler objects with extremely high luminosities (HDE 331319 and IRC+10420). The B[e]Ds is a growing group of objects with very strong emission-line spectra, some of which show direct evidence of the presence of a hot and a cool star in the system. Their basic properties and connection to other groups of binaries are discussed, and a new list of members is presented. Fundamental parameters and chemical composition of an unusual F-supergiant HDE 331319 and recent results on a fast evolving object IRC+10420 are also reported.

The star β Pictoris is not in itself very remarkable; however, it is surrounded by a dust disk that is much more prominent than any other main sequence star’s disk. The proximity of β Pic and the nearly edge-on viewing geometry of the disk enhance its appearance, but do not fully account for the disk’s prominence. While it is possible that β Pic’s disk is intrinsically unusual, a more likely explanation is that β Pic is simply a very young (~ 20 Myr old) main sequence star with a consequently denser second-generation debris disk remnant of its protostellar disk than possessed by older main sequence A stars.

A simultaneous photometric and spectroscopic analysis of the purported early-type overcontact binary TU Muscae is presented. With a well-behaved light curve and a mass ratio far from unity, if TU Mus is indeed an overcontact system, it presents an interesting challenge for 3-D stellar evolution codes, like the Djehuty code, that will be applied to early-type overcontact binaries. The analysis shows TU Mus is slightly overcontact and that a detailed treatment of the reflection effect is important for modeling the light curves.

RY Scuti is a massive contact binary in a critical Roche-lobe overflow phase, and it may be an immediate progenitor of a WR+OB binary system like V444 Cygni. It may also have something in common with the eruptive binary HD 5980 in the SMC. RY Scuti is a nearby eclipsing binary, but basic parameters like the mass and evolutionary state of its individual components seem difficult to nail down because it is a common-envelope system. It is also surrounded by a compact double-ring nebula with geometry and kinematics that have interesting implications for its mass-loss mechanism. Some recent results of high-resolution imaging and spectroscopy of the nebula are reviewed here.

A detailed study of the periods and light curves of binaries AK Her, AP Leo, AB And and AM Leo is presented. Based on the study of the O – C curves, we find that the period variation of each system contains several components with different frequencies, and we suggest that the periodical variations in the periods are likely influenced by different mechanisms. Based on the study of the light curve changes, we find that the light curves exhibit two kinds of variations: rapid variations and long-term variations. We investigate the physical mechanisms which may underlie the variations of the period and the light curve of each system and obtain some new conclusions. According to the characteristics of the rapid light variation in these systems, we suggest that the rapid change in the light curve is probably caused by pulsation of the common envelope, and that the mechanism(s) causing the pulsation may be mass transfer through the inner Lagrangian point L1 or its variation. Finally, the evolutionary trends of these systems are discussed, and we suggest that these systems may be progenitors of cataclysmic variables.

Variability of the light curves of the short-period eclipsing binary system GR Tau (, almost-contact binary) is studied. It is found that GR Tau experienced both the state which is characterized by asymmetric light curves and the state characterized by symmetrical light curves.

Light curves of the W Ursae Majoris binary AH Cancri obtained in 1973 and 1988 show a remarkable change in shape. Earlier curves have rounded minima and eclipses appear to be partial; later curves have flat-bottomed minima indicating total eclipses. The 1973 curves are consistent with a system in overcontact with an orbital inclination of approximately 65°. Such a low inclination, however, is incompatible with the -duration flat-bottomed eclipse seen in the more recent light curves. Intrigued by this puzzle we decided to make new photometric observations. We present CCD photometry in V and R obtained with the Southeastern Association for Research in Astronomy (SARA) 0.9-m and Buehler Observatory 0.4-m telescopes. We solve the new light curves and find a high-inclination (i ≈ 84°), low-mass-ratio (q ≈ 0.145) model fits the observations reasonably well. In the post-1988 light curves, limb darkening causes eclipses of the cooler star to be deeper than those of the hotter star. Times of minima suggest a possible third body interaction.

The eruptive variable V838 Mon was discovered on Jan 6, 2002. Due to a subsequent phase of almost constant brightness and a spectral appearance which is unlike classical novae, speculations have been made about its nature. Either it was a very peculiar, slow nova defining a new class, an eruptive event in an evolved star as in the case of Sakurai’s Object but in a much earlier phase, or something completely different.

The story of HD 101065, Przybylski’s star, is one of a forty-year controversy over the nature of what is arguably the most peculiar star in the sky, a controversy that is only now being resolved fully. Our current understanding is that HD 101065 is the coolest (Teff ≈ 7400 K) and the most peculiar of the Ap SrCrEu stars. The existence of this most peculiar star, and other Ap stars, has been the source of some very interesting stellar astrophysics with applications far wider than the understanding of just the stars themselves.

The examination of high resolution spectra of two Ap stars, HD 965 and HD 217522, discloses a spectral appearance similar to Przybylski’s star. Here we present the preliminary results of a comparative study of all three stars. Further, we discuss the possibility of having a good spectroscopic indicator of magnetic fields in Ap stars. In all three studied stars the strong Lu II line at λ 5984 Å is present and very likely not affected by significant blends. Its hyperfine structure has been recently measured and we show the results of a model that accounts for the Paschen-Back effect on hyperfine structure.

We have investigated possible models for the evolutionary status of the black-hole soft X-ray transient Nova Scorpii. We propose that it is a main-sequence star in which convective overshooting, or some equivalent mixing, occurs at the core-envelope boundary. Recent detections of chemical pollution on the surface of the secondary suggest that the black hole formed in a supernova whose ejecta left and fell back at a sufficiently low velocity to accrete on to the secondary. We examine the effects of increased opacity, increased metallicity and reduced hydrogen abundance on the evolution of the secondary in the hope that these might lead to an alternative scenario. All these only exacerbate the problem.

The greater the spectroscopic detail observed, the more one appreciates that stars are individuals. Phenomena exhibited by bright stars illustrate some of the wealth yet to be unearthed – and explained.

Astronomers possess a heritage of enormous wealth and potential: historic observations detailing the foundations of astrophysics, witnessing the observable universe decades ago, and recording any number of periodic or sporadic phenomena. If those observations were available on-line, what an enormous resource they would constitute for research. But they are not; they are on non-digital photographic plates, and we risk losing all that information for ever unless some measures are taken fairly soon to transfer it digitally to a more accessible medium.

A star is exotic because, in some way, it extends our knowledge of how stars behave. As we make new observations we discover new phenomena that we do not understand. As we approach an understanding, those phenomena seem less exotic. That is nature. IAU Colloquium 187 set out to discover how far our knowledge of stars now reaches. This is a personal commentary on the proceedings.