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This is the last triennial report of Commission 42 for this millennium. A great deal has been accomplished in the study of Close Binary Stars (CBS) since the discovery of the first close (eclipsing) binary, Algol, in 1783 by John Goodricke. Now, over 10,000 CBS (most eclipsing variables) are known. More than 5000 of these CBS were discovered over the last several years alone! And many more are expected to be detected over the next few years. Most of these stars were found as spin-offs of microlensing surveys. Interestingly, nearly half of these stars are found outside our Galaxy, primarily in the Magellanic Clouds and M31. Every type of star is represented as a member of a close binary. These include main sequence (as well as pre-main sequence) stars, giants, and supergiants, with the entire possible range of of spectral types and masses represented. Moreover, “dying” stars and “dead” stars, such as white dwarfs, neutron stars, black holes, and, more recently, even brown dwarfs and giant planets (e.g., 51 Peg) have been found as members of close binary systems.

Revised orbits are presented for the double-lined binary WR+O systems HD 63099 (WR9) and HDE 320102 (WR97). The orbit derived for WR9 from OVI emission and HeII absorptions is considerably different from that previously published based on the CIVΛ4658 emission line velocities. WR97 is found to have a period of 12.6 days and small minimum masses, probably due to a low orbital inclination. Two stars in our Galaxy, WR30a and WR70, and two in the Magellanic Clouds, Brey44 and AB7, show radial velocity variations of emission and absorption lines in opposite sense. Although no periods are yet available, preliminary values of the mass ratios can be estimated from the velocity variations.

Spectral observations of the WN3p star WR46 (HD 104994) obtained during June 1993 and January/February 1994 display large amplitude radial velocity variations of the strong emission lines Nv 4603-19Å and HeII 4686A, on a time scale of a fraction of a day. The most probable period found is 0.311 d, similar to the photometric period found by previous authors. The amplitude of the radial velocity variations of Nv emission is almost twice that of HeII. Noting the similarity of WR46 with low mass X-ray binaries, we suggest that the emission line spectrum corresponds to that of a luminous accretion disk in an evolved binary system.

Optical spectroscopic observations of the eclipsing binary WR star HD 5980 in the SMC, obtained during different epochs, show a remarkable change of the WR type spectrum from spectral type WN3-4 to WN7-8. Radial velocities of the WR emission lines from spectra obtained in August 1992, indicate an orbital motion corresponding to the secondary component which is in front of the system during the primary eclipse. We compare the RV curves and phase-dependent line-width variations observed in 1992 with previously published data.

field of 2 square degrees centered in the position of HD 197406 (a spectroscopic binary composed by a WN7 star + compact companion), has been surveyed in the HI 21 cm line and in the 1420 and 408 MHz radio-continuum, using the synthesis radio-telescope of the Dominion Radio Astrophysical Observatory (Canadá). The spectral maps show the existence of a nearly complete ring-shaped HI shell (R₅≃30 pc, vₑₓₚ≃ 5 km/s, Mₕᵢ≃ 600 M⊙), and, immersed within this shell, a small spherical bubble concentric with the star (R_b≃=3 pc, vₑₓₚ≃ 4 km/s, Mₕᵢ (missing)≃3 M⊙). From these observations, a kinematical distance of 5 kpc is derived for HD 197406. We did not find thermal or non-thermal radio-sources associated with the binary system. Our observations suggest that the large shell has been created during previous evolutive stages of the binary, while the small bubble has been recently blown by the WR wind., Asociación Argentina de Astronomía