The blue straggler F190 is a member of the old open cluster M67. We argue that F190 may still be in the final stages of the mass transfer that has made it into a blue straggler. We use the turnoff mass of the cluster and the mass function derived from the spectroscopic orbit for F190 to constrain the masses of each member of the binary, both before mass transfer and now. We find that the mass transfer must have been nearly 100 percent efficient.

SS Lac, a probable member of the open cluster NGC 7209, and a target system of several apsidal motion programs and of our binaries-in-clusters program for the past decade, is no longer eclipsing. The sudden disappearance of eclipses is now well documented. Zakirov and Azimov (IBVS 3487, 1990) and Schiller et al. (BAAS 23, 879, 1991) announced the current nonexistence of eclipses based on extensive photometry. Photographic and visual observations indicate cessation in the 1950–1951 season. Here we describe recent radial velocity work, modeling of published light curves, plans for further investigation and discuss implications of the cessation for system evolution.

The three eclipsing binaries among the blue stragglers of the globular cluster NGC 5466 have been modeled. Two of the systems are contact systems and the third is a short-period Algol system. The results indicate that the systems are well on their way to merger, but the implications for the origin of blue-stragglers are less clear.

Photoelectric BVRI light and radial velocity curves of the 0.41d period eclipsing variable have been analyzed with a new, simplex-enhanced version of the Wilson-Devinney light curve program, and used to explore detached, semi-detached, and contact solutions. The system is best modeled as a W-type W UMa system, with contact parameter, f = 0.44, although at time of writing, we cannot rule out the possibility of an A-type system.

For a sample of halo binaries, we find that the transition between circular and eccentric orbits occurs at a period of at least 18.7 days. This is consistent with the Goldman & Mazeh theory of tidal circularization on the main sequence.

We present spectroscopic orbits for 4 eclipsing binary systems in the Magellanic Clouds. The minimum masses that we find for the binary components in the LMC are: 34 + 17 M⊙ for HV 2241 and 26 + 15 M⊙ for HV 2543, and for the ones in the SMC: 21 + 25 M⊙ for AzV 73 and 17 + 19 M⊙ for HV 1620.

Absolute dimensions and the distance modulus have been established for the early-type eclipsing binary HV 2226 in the SMC. Analyses of the new radial velocities reported here, and CCD light curves published by Jensen et al. (1988) yield component masses of 9.3 ± 0.7 and 5.6 ± 0.5 M⊙, respectively. The radii are 5.6 ± 0.2 and 5.3 ± 0.2 R⊙ with the secondary component filling its Roche lobe which implies that HV 2226 must have evolved through a case A mass-transfer process. A distance modulus of (mv – Mv )0 = 18m.6 ± 0m.3 is derived, marginally lower than the adopted mean of 18m.9 for the SMC. The position of HV 2226, however, indicates that it is in fact situated in the near side of the SMC. In the present case, the accuracy of this estimate is limited mainly by the uncertainties of ≈ 2000 K in the effective temperatures. We point out that distance moduli with uncertainties of ± 0m.15 can be achieved from accurate radial velocities, light curves and colour indices of eclipsing binaries; such systems in the SMC and LMC are therefore promising distance indicators and work on further selected candidates is in progress.

We present linear polarization observations of two binary systems with early Of type components, namely Sk-67°105 in the Large Magellanic Cloud, and LSS 3074 in our Galaxy. Both binaries show phase-locked polarization variations, from which we determined orbital inclinations for the systems.

B, V and Ic photometry of the eclipsing binary HV 2274, located in the LMC, was obtained with the CCD system at the Mount John University Observatory, Lake Tekapo, New Zealand during 1990. Over 100 data points were acquired in each filter to an estimated precision of 0.02 mag. The flat maxima evident in the light curves suggest that the system, which is currently classed as an interacting candidate, should probably be considered as a detached one. A revised orbital period based on the inclusion of current data is presented. Eclipse timings indicate an eccentric orbit. An apsidal period in the vicinity of 120 yr is likely.

Close-binary planetary-nebula nuclei (PNNs) provide direct evidence for occurrence of a common-envelope phase in binary-star evolution. Their descendants are V471 Tauri-type detached binaries, cataclysmic binaries, and possibly Type I supernovae. Thirteen close-binary PNNs are now known from periodic photometric or radial-velocity variations, or from composite optical/UV spectra. At least 10% of PNNs are close binaries, a fraction more than sufficient to account for the formation of all of the cataclysmic variables in the solar neighborhood. The Abell 35-type binary PNNs, a class with three known members, contain rapidly rotating, chromospherically active late-type primary stars along with extremely hot companions detected with the IUE satellite.

We here report the results of a systematic investigation of how binary interaction affects the presupernova evolution of massive stars and the resulting supernova explosions. We summarize the various types of binary interaction and the evolutionary scenarios in which they are realized. We also present the results of a series of hydrodynamical calculations which model the supernova explosion for various progenitor types and discuss their observable characteristics.

Using simultaneous evolutionary calculations of both components of a massive binary, it is shown that the initial secondary component can explode before the primary, if Roche lobe overflow occurs on the main sequence. Also, it is found that initially wide binaries are more likely to come into contact than close ones.