Five semi-detached systems have been identified having detached components with spectral types G or K. These stars form a sequence having temperature decreasing with increasing mass, in contrast to the “classical” Algols with hotter detached components having properties roughly approximating those of detached main sequence stars. The status of the cool Algols is discussed briefly. A second group of 3 detached components in Algols is identified having higher temperatures than main sequence stars of the same mass.

A total of 1,037 UBV observations was made for the latest eclipse of Zeta Aur in 1987–1988 at Yonsei University Observatory. These observations furnish UBV light curves which cover the phases before, during, and after the eclipse. The current issues regarding the radius variations of K supergiant component are discussed.

FK Com is an enigma among active cool stars. A rotationally driven magnetic dynamo is an explanation for activity. Youth and binarity are two causes of rapid rotation, but FK Com is old, single, and rotating near breakup. Much studied optical and ultraviolet data have not revealed the cause of its unusual activity. It is an important object in a more complete understanding of close binary star evolution and of the dynamo theory of magnetic activity. In 1989, we executed a coordinated ultraviolet and intensive optical spectroscopic and photometric campaign to better elucidate its characteristics. Data relevant to its evolutionary status, namely its radial velocity variations, will be discussed here, while an in depth study of the chromospheric activity will be deferred to a more detailed publication.

Orbital elements for 8 non-Mira S stars (derived from CORAVEL observations and from Griffin 1984) are compared with those of barium stars. In all but one case, the mass functions are compatible with white dwarf companions. No periods shorter than 600 d are found, while the 5 orbits with 600 < P(d) < 900 all have e ≤ 0.1, in contrast with the situation prevailing for barium stars. It is suggested that the hypothesis of an evolutionary link between barium and non-Mira (no Tc) S stars can be reconciled with these differences provided that these S stars are low-mass stars populating the first giant branch instead of the asymptotic giant branch, as usually thought.

A long-term, high-accuracy, differential uvby monitoring of a sample of 19 barium stars revealed that HD 46407, a well known barium star with an orbital period of 458 d, is an eclipsing binary. The eclipse (of the companion by the barium star) was most clearly seen in November 1988, when a dip of 0.02 mag (in y) having a FWHM of about 10 d was recorded in the lightcurve. Confirmation of the eclipsing nature of HD 46407 was also obtained in February 1985 and in February 1990. A shallow secondary eclipse (extending over about 50% of the orbital period) seems to be present as well. The b – y index is marginally variable, while v – b color variations are correlated with the y variations, in the sense that the system appears redder when it is fainter. We suggest that these variations originate in the scattering of the red-giant light by dust particles trapped (in a wide ring or shell?) around the (compact) companion. The eclipsed light would then be the light of the red giant backscattered by the dust around the companion.

We concentrate on the application of centimeter wavelength observational data to the coronae of rapidly rotating active dwarf stars. In particular we seek insight into coronal loop geometries, and their possible relevance to the magnetic braking mechanism, which must play a key role in binary evolution scenarios for such stars.

Optical spectroscopic, photometric, and infrared photometric observations of the symbiotic-like star MWC560, which underwent a prolonged ‘outburst’ during 1990, are presented. Both the magnitudes and timescales of outbursts are similar to other symbiotics, and related systems. The large ejection velocities observed, and the transient nature of the highly blue shifted absorption components, are quite atypical, however.

High spatial resolution observations R Aqr have been carried out with the HST/FOC. R Aqr is the nearest symbiotic star, i.e. an interacting system consisting of a cool giant star and a hot ionizing source embedded in a larger and complex nebula. We suggest, here, that the binary system is composed of a Mira and a hot stellar source with a radiation temperature of T * ≈ 40 000 K, a luminosity of L ≈ 10L⊙ and a radius R ≲ 0.1 R⊙. Mass transfer between the two components of the system occurs via capture of the Mira wind. Of the plausible mechanisms that may produce the R Aqr jet, an accretion/ejection scenario or the collision of winds seem to be unlikely, but spectral observations of the core are needed to conclude. Another possible origin is based on a spherically symmetric stellar wind that sweeps out a cavity in an ambient medium. This bubble elongates in the directions of least resistance, and matter eventually flows out through two symmetric nozzles. Comparison with models shows that the emission in the NE and SW outer features of the jets is due to a radiative shock but the pre-shock gas must be partially photoionized by the central hot stellar source.

We present the basic properties of symbiotic novae, and show how they differ from classical novae. Differences are observationally particularly noticeable in the luminosity curve, the rise of which is much slower, but its return to pre-outburst level takes much longer than in classical novae. Special emphasis is given to the intial phase, for which two different evolutionary paths have been observed. The outburst may lead into a supergiant phase lasting for several years, which is being followed by the nebular phase, or it may lead straight into the nebular phase. The total energy radiated during an outburst is at least as large as the energy loss of classical novae. Mass-loss during outburst may be sufficiently small to lead eventually to a supernova on the white dwarf.

We determine bolometric light curves and total energies radiated away during the outburst of symbiotic novae. Time integrated lower limits to the total energy of 0.9×1046 <E[erg] < 7×1046 are found. Thus, the output is comparable to, or larger than the total energy production of a classical nova outburst. From the mass-luminosity relation we find the underlying stellar masses to be 0.5 < M/M ⊙ < 1.1.

We have investigated the nature of P Cygni-like features in the high resolution IUE spectra of the symbiotic variables BF Cyg and EG And by looking for orbital phase-dependent variations in the structure and velocity of the C IV (1550 Å) resonance doublet in 10 archival IUE high-dispersion spectra of these systems and by comparing their profiles with P Cygni-like features seen in IUE high-dispersion spectra of other symbiotic stars. For BF Cyg, we find maximal P Cygni absorption equivalent widths and terminal velocities of ~ 900 mÅ and ~ −240 km s−1 respectively, full emission velocity widths at the 10% intensity level of 300–400 km s−1, depending on phase, Φ, variations in the width of the P Cygni absorption, shortward velocity shifts of the C IV emission line in all but two orbital phases, relative to the C IV velocity at Φ = 0.01, and absorption sub-structure within the C IV P Cygni lines which coincide in velocity from image to image. In EG And the C IV P Cygni absorption equivalent width is, on average, 300 mÅ with a terminal velocity of −217 km s−1 (which includes the systemic radial velocity contribution of -93 km s−1). The presence in one image, of a strong absorption feature at He II (1640), having a precise velocity coincidence with the C IV P Cygni absorption component, suggests that the absorbing material responsible for both line features is associated with outflow and P Cygni self-absorption from the vicinity of the hot component. In both BF Cyg and EG And, the structure and behavior of the P Cygni profiles may rule out their origin in the red giant wind or in an expanding circumbinary shell. Our results support the hot component wind interpretation of Mikolajewska et al. (1989). Motivated by the low-mass white dwarf shown to be present in BF Cyg (Mikolajewska et al. 1989), we have carried out quasi-static evolutionary model calculations with accretion onto a 0.55 M⊙ white dwarf accreting at the rate 2 × 10−8 M⊙ yr−1. The sequence of 3800 quasi-static models, the first to be reported for a low-mass hot white dwarf (Mwd < 0.8 M⊙) accreting at a high rate, yields an unexpected outburst behavior in response to accretion at that rate, when compared to evolutionary sequences with accretion onto higher mass white dwarfs. A series of three major thermonuclear shell flashes and one lower energy shell flash is revealed with the timescale during outburst and the inter-outburst timescale substantially shorter than expected for a 0.55 M⊙ white dwarf. Preliminary results on other sequences are also reported. Implications for the observations of symbiotic systems thought to contain low-mass white dwarfs, are discussed.

We present high-speed photoelectric observations of a 13th-mag cataclysmic binary BZ Cam (=0623+71), gathered in 1989 and 1990. The data were analyzed by means of the Fourier technique. The most prominent feature detected in the power spectrum is a 3h36m period which we ascribe as being a photometric orbital modulation. This period is significantly different from the periodicity previously known from spectroscopic observations. The power spectrum shows also quasi-periodic oscillations of shorter time-scales but any conclusions about their stability can not be drawn yet.

Orbital and stellar parameters of the massive X-ray binary LMC X-4 are rediscussed with particular attention to a possible “higher mass” (> 1.4 M⊙) neutron star in the system.

Detailed analysis of numerous observational data for Her X-1 / HZ Her shows that Her X-1 has a rare type of accretion regime: impulses of mass transfer every 0.81 d. Semi-empirical analysis show complicated 3 D type of gas flow near the outer disk rim of Her X-1: interaction of gas stream with disk forms blobs, which are disintegrated into small drops of matter (“sprays”) by an interaction with gaseous corona around the outer disk rim. Fall of the sprays on different parts of the disk decreases time of accreting mass flow along disk radius. Evaporation of sprays is a source of mass supporting the disk corona. The corona and disintegrated blobs (sprays) have numerous observational manifestations in optical and X-ray ranges. Evaporation of the corona from the Roche lobe could be an important source of orbital angular momentum loss and, consequently, a source of orbital period variation.

Using a 3-dimensional hydrodynamical code, based on the Smooth Particle Hydrodynamics (SPH) method, we have simulated the case of wind accretion. Several configurations were studied:

• - homogeneous mass flow

• - wind with a density gradient

• - wind with a velocity gradient

In each case, the accretion rate as well as the accreted angular momentum has been calculated. Comparisons were done with other simulations published in the literature and especially with the two currently existing 3-D simulations. According to one of these group (Matsuda et al., 1990) resolution is very critical in determining the accretion rate as well as to determine if the flow is stationary or not. We have done simulation at various resolutions and we confirm its importance for the deduced accretion rate. However, our simulations do not seem to show any non- stationary behaviour.

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.

This group of stars consists of 4 systems, also called helium cataclysmics. Three of them show photometric variations and have been studied by the Whole Earth Telescope (WET), which have revealed multiperiodic light curves showing the signature of g-mode non-radial pulsations on the accreting star. The combination of accretion and g-mode pulsations gives a unique opportunity to test models for the accreator's structural changes in response to accretion. IUE-spectra provide additional physical parameters.

Recent spectroscopic observations of the interactive binary SS 433 with the ESO's New Technology Telescope show that the compact object is a neutron star. We note that the huge mass transfer rate (which may well be the reason for the uniqueness of SS 433) suggests that a significant fraction of the mass lost from the normal star actually settles on the neutron star. This may have important consequences for the structure of the accretion disk and for the formation of jets in this peculiar system.

In 1971 Roger Griffin and Jim Gunn began monitoring the radial velocities of most of the members brighter than the main-sequence turnoff in the old open cluster M67, primarily using the 200-inch Hale Telescope. In 1982 the torch was passed to Dave Latham and Bob Mathieu, who began monitoring many of the same stars with the 1.5-meter Tillinghast Reflector and the Multiple-Mirror Telescope on Mt. Hopkins. We have successively combined these two sets of data, plus some additional CORAVEL velocities kindly provided by Michel Mayor, to obtain 20 years of time coverage (e.g. Mathieu et al. 1986). Among the stars brighter than magnitude V = 12.7 we have already published orbits for 22 spectroscopic binaries (Mathieu et al. 1990). At Mt. Hopkins an extension of this survey to many of the cluster members down to magnitude V = 15.5 has already yielded thirteen additional orbital solutions, with the promise of many more to come.

For the past 9 years we have been monitoring the radial velocities of 13 blue stragglers in the old open cluster M67. For the 9 blue stragglers with rotational velocities no larger than about 100 km s−1 we have used the CfA digital speedometers to measure more than 500 radial velocities. To get reliable velocity correlations we use synthetic rotating templates computed from a grid of Kurucz model atmospheres. Four of the blue stragglers rotate too rapidly to allow successful velocity correlations with the CfA instruments. For three of these we have used a CCD spectrograph at Kitt Peak and similar reduction procedures (Morse et al. 1991.