Initial results are presented from a study of Hγ profiles in the two interacting binaries KX And and RX Cas of W Serpentis type. The used CCD spectra with a resolution of 0.13Å/px were obtained with the 2.2m telescope and the Coudé spectrograph at the German-Spanish Astronomical Center at Calar Alto/Spain.

The interacting binary V367 Cyg is contained in the original list of W Serpentis stars discovered by Plavec and Koch (1978) in their initial UV study and has been subject of numerous studies, both photometric and spectroscopic.

Although KX And (HD 218393, MWC 397) has been observed since the beginning of our century, we have no reliable model of this peculiar emission-line object. Published papers (e.g. Plavec et al. 1982; Kriz and Harmanec 1975 and references therein) indicate that it is a B+K W Ser-type binary with a period of 38.9 days. This paper presents a summary of intensive observations carried out during the last fifteen years.

The observational material used consists of 65 coude spectra obtained with the Ondrejov 2-m telescope, UBV photometry obtained at Hvar Observatory and 28 archival IUE images. The radial-velocity and photometric data are combined with those found in the literature. A PDM period search over the interval 1 to 1000 days unambiguously indicates the 38.9-day period both in RV and photometric data.

A recent survey of EA eclipsing binaries by the Parkes 64-m telescope operating at 8.4 GHz detected 15 out of 47 systems on at least one out of the 10 nights surveyed. The detected systems were HD 6882 (ξ Phe), HD 36486 (δ Ori A), HD 39780 (TZ Men), HD 57167 (R CMa), HD 58713 (RY Gem), HD 74307 (S Cnc), HD 132742 (δ Lib), HD 147683 (V769 Sco), HD 161741 (V393 Sco), HD 163708 (V1647 Sgr), HD 16871Q(XZ Sgr), HD 183794 (V822 Aql), HD 187949 (V505 Sgr), HD 199005 (KZ Pav), and HD 207098 (δ Cap).

A full account of the observations and interpretation has been submitted to The Astrophysical Journal.

About one-half of the 15 detections refer to main-sequence pairs of spectral types earlier than F and the remainder are classical Algols.

Synchronous rotational velocities have been calculated for 91 Algol-type systems for which the radii of the components and orbital inclinations have been published. New values of V sin i have been measured for some of these systems. The frequency of components rotating near synchronism (F less than 1.5) is found to be higher for unevolved than for evolved systems. For Algols with periods less than 10 days and radii greater than 0.2, synchronous rotation is found to be the rule. There are 50 components of spectral type B and 44 of spectral type A in systems with periods shorter than 10ḍ The shortest period in which synchronism is found is 4 days for the A-type components and 2 days for the B-type.

This work is concerned with binary systems that we call ‘moderately close’. These are systems in which the primary (by which we mean the initially more massive star) fills its Roche lobe when it is on the giant branch with a deep convective envelope but before helium ignition (late case B). We find that if the mass ratio q(= M1/M2) < qCrit = 0.7 when the primary fills its Roche lobe positive feedback will lead to a rapid hydrodynamic phase of mass transfer which will probably lead to common envelope evolution and thence to either coalescence or possibly to a close binary in a planetary nebula. Although most Algols have probably filled their Roche lobes before evolving off the main-sequence we find that some could not have and are therefore ‘moderately close’. Since rapid overflow is unlikely to lead to an Algol-like system there must be some way of avoiding it. The most likely possibility is that the primary can lose sufficient mass to reduce q below qcrit before overflow begins. Ordinary mass loss rates are insufficient but evidence that enhanced mass loss does take place is provided by RS CVn systems that have inverted mass ratios but have not yet begun mass transfer. We postulate that the cause of enhanced mass loss lies in the heating of the corona by by magnetic fields maintained by an α-ω dynamo which is enhanced by tidal effects associated with corotation. In order to model the the effects of enhanced mass loss we ignore the details and adopt an empirical approach calibrating a simple formula with the RS CVn system Z Her. Using further empirical relations (deduced from detailed stellar models) that describe the evolution of red giants we have investigated the effect on a large number of systems of various initial mass ratios and periods. These are notable in that some systems can now enter a much gentler Algol-like overflow phase and others are prevented from transferring mass altogether. We have also investigated the effects of enhanced angular momentum loss induced by corotation of the wind in the strong magnetic fields and consider this in relation to observed period changes. We find that a typical ‘moderately close’ Algol-like system evolves through an RS CVn like system and then possibly a symbiotic state before becoming an Algol and then goes on through a red giant-white dwarf state which may become symbiotic before ending up as a double white dwarf system in either a close or wide orbit depending on how much mass is lost before the secondary fills its Roche lobe.

Radio emission from close binary systems has long been detected in Algol and other systems. RS CVn systems have been found to be the most powerful and active. The RS CVn binaries are also known to show strong chromosferic and transition region emission line fluxes, that are one or two orders of magnitude higher than those from single stars of similar spectral type. This enhanced activity seems to be connected to the rapid rotation due to the tidal interaction in the system. The Algol binaries are semi-detected close binary systems formed by an early type main sequence primary and a late type giant secondary, while in the RS CVn both components are late type stars of about the same mass, the secondary being a giant or subgiant.

The Algol binaries and RS CVn differ also in their evolutionary history. However, since the spectral type and probably the internal structure of the secondary components of Algols appear to be similar to that of the secondaries of RS CVn systems, and they both are synchronous fast rotators in close binaries, we would also expect that the secondaries of Algol systems to show some kind of activity.

Most Algol-type variables are believed to be close, semi-detached binaries which have evolved from a rapid mass-transfer phase, which reversed the initial mass-ratio, to a relatively quiescent stage where only small-scale transient events perturb the dynamical and the photo-metrical properties of the system.

Of all Algol-systems, only the prototype Algol (β Per) itself is bright enough to be traceable in astronomical records reaching back more than 2000 years. Evidence based on medieval stellar lists and 19th-century visual observations strongly suggest that the intrinsic colour of Algol has been subject to substantial variations within historical times. On a few occasions Algol was apparently observed as reddish, which is at variance with its present blue-white appearance (B-V = −0.05 to +0.10).

We present light curve solutions for the non-synchronously rotating Algols RW Mon and RW Tau, and we illustrate how rotation rates are determined from light curves. We find RW Mon’s primary component to spin at about 5 times the synchronous rate, which confirms the indication of fast rotation from reported emission line activity. RW Tau turns out to be only a mildly rapidly rotating Algol system, and our light curve solutions do not yield any firm value for the rotation rate of the primary component. It is suggested that continued efforts should be made to do good quality line broadening studies in order to find rotation rates for systems with only modest degrees of rapid rotation, and in order to further test photometric rotation rates against those of line broadening studies.

The star AY Vulpeculae was recognized as variable and labeled as an Algol-type system by Hoffmeister, (A.N. 242, 133, 1931). Koch et al. (I.B.V.S. 1709 1979), included it in their list of eclipsing binaries for which photoelectric work was needed. The system is faint, but because its primary minimum is very deep it is of astrophysical interest. The observations of the present investigation represent the first definitive photometric study made of AY VUL and is one of several systems with periods greater than two days being observed with the 1.0 meter Ritchey-Chretian reflector at the Flagstaff Station . A total of 1242 observations of AY Vul (406 in V, 417 in B, and 419 in U) were obtained on 12 nights in 1986.

Orbital elements for AY VUL were obtained by using the Wood model, and the calculations were performed on the VAX 11/750 computer at the Flagstaff Station of the U. S. Naval Observatory. AY Vulpeculae can be regarded as a classical Algoltype semidetached system in which the secondary component fills its Roche lobe, while the primary lies well inside its own lobe. Both eclipses are partial. The orbital elements are listed below.

Simulations of the Algol-like binary CX Draconis, combined with IUE observations of the stream of material escaping the system can place limits on the inclination of the system and give estimates, via line profile synthesis, of the mass-loss rate at the L1 point.

Complete UBV light-curves of RR-Lep and RX-Hya have been obtained during 1983-87 seasons. Preliminary elements were computed using modified Wellmann’s method. With these parameters as inputs Wilson-Devinney program was executed for Blue and Yellow passbands simultaneously in detached and semi-detached modes for both the systems. The semidetached mode fitted better than the other solution for both the systems. For RR-Lep, the absolute dimensions were computed by assuming the primary to be a slightly evolved main sequence star. For RX-Hya, the absolute dimensions were computed using Struve’s spectroscopic data. The following table gives all the elements for both the systems. The secondaries of both the systems are overluminous for their masses suggesting that they have lost considerable mass.

The analysis of 149 radial velocities of V923 Aql from 1927 to 1987 revealed that the observed RV variations arise from a superpositon of cyclic long-term velocity variations of variable amplitude and cycle length / 20≦2K≦65 km.s-1, 1800d≦P≦2400d/ and an orbital motion with a period of 214.75 days and an amplitude 2K=12.4 km.s-1. The binary system consists of a B5-7 e primary and low-mass /about 0.5 M⊙/ secondary separated some 250 R⊙. Both, the long orbital period and low mass ratio are typical of /interacting/ binaries containing a Be star. The observed cycle length of the long-term changes are very similar to those observed for ɽTau, the only Be binary with the long-term variations known to date. V923 Aql thus becomes the second representative of binary Be stars, for which it is conceivable to interpret the long-term variations by an elongated envelope, revolving due to the attractive force of the secondary, and'formed by the process of mass transfer from the secondary to primary, as predicted by the binary model of the Be phenomenon.

This binary system, according to Semeniuk and Paczynski (1971), is very interesting because it is probably in a phase of rapid evolution through the Hertzsprung gap in the HR diagram and shows apsidal motion (Battistini et al. 1974) .

The system was Observed at the Bologna Astronomical Observatory in UBV because the only known light curve (Kron 1935) is insufficient to give appropriate orbital elements (Kopal 1940, Ramella et al. 1980) and it is impossible to fit photometric elements with spectroscopic results (Batten 1962). The observations started in 1970 and ended in 1973; in 1980 the system was reobserved to complete light curve coverage.