In part I (De Greve and Packet) we have investigated the occurrence of reversed phases of mass-transfer during Case A evolution in close binaries. If the initial period of a system is shorter than 1 - 2 days (Early Case A) the reversed phase starts before core hydrogen exhaustion of the gainer (part I). This type of evolution is characterized by at least two phases of slow mass-transfer.

We have computed the evolution of four Early Case A systems with initial masses of the loser equal to 3 Mo and 5 Mo. These four systems start mass-exchange when Xc of the primary has decreased to 0.525 (75% of its initial value). They all experience two phases of slow mass-transfer.

We find that both phases have about the same duration for all systems. The mass ratios are clearly distinct, being closer to unity during the first phase. In the Hertzsprung-Russell, mass-radius and mass-luminosity diagrams both components remain close to the main-sequence band during slow mass-transfer. Evolution as an Algol is ended when both components overflow their outer critical surface after a second reversal of the mass-transfer.

Observed Algol systems evolving in Early Case A are scarce. A search thruogh the catalogue by Giuricin et al. gives us the following candidates: X Tri, SX Aur and V Pup. Based on their mass ratios, SX Aur can tentatively be assigned to the first phase of slow mass transfer and X Tri to the second phase. For V Pup (which is more massive) this choice can not be made with certainty.

We present a table of results from our survey of Algols, conducted with the Lick Observatory ITS scanners and the IUE spectrometer.

In order to check the evolutionary status and theoretical models of eclipsing binaries of Algol type, a reliable determination of their absolute dimensions is needed. In this communication, we compare the most commonly used methods to derive absolute parametors in single-lined aclipsing binaries. Let us first assume that the mass function, f(m), is known from the analysis of the radial velocity curve while the relative radii and orbital inclination are derived from the light curve. The determination of absolute parameters is then equivalent to the obtention of the mass ratio, q = m2/m1. The following methods are available to estimate q from observed parameters — over-all errors being estimated for observational uncertainties of the order of 5 % in relative radii and temperatures and 15 % in f(m) —:

1. 1. qs: It is assumed that the primary component follows the mass-luminosity relation for main-sequence stars. This procedure provides qs with an uncertainty of about 10 %.

2. 2. qsD: It is assumed that the secondary component fills its Roche lobe. Errors of at least 15 to 20 % are expected from this procedure mainly due to its high sensitivity to small variations in the observed value of r2, particularly if r2 > 0.2.

   Both methods can be used together when f(m) is doubtful, or completely unknown, but errors can not be expected to be better than in case 2.

3. 3. qn: It is assumed that the primary component rotates synchronously in a circular orbit. This assumption is difficult to adopt due to the expected transfer of angular momentum through mass transfer and the value of qn is estimated with about 20 to 30 % error.

4. 4. qED: It is assumed that the primary component, is well reproduced by standard evolutionary models within the main sequence. Adopting a grid of models for a given chemical composition, an iterative procedure in the log Ti,.–log g plane permits the determination of m1 and thus q. This method is equivalent to (1) but avoids errors due to evolution from the ZAMS to the TAMS, not taken into account in the previous method, and allows to reach a higher accuracy, around 5 %, except for those primary stars located around the TAMS, where the determination of mi is not unique.

In order to investigate the effects of irradiation on the spectra of the cooler components of Algol binaries, a modified version of the Upsalla Model Atmosphere code (U.M.A.) has been used. The upper boundary condition was changed to take into account the external radiation field and an automatic procedure to prevent numerical oscillations was introduced. In order to simulate the external flux from the hot component we have used the Kurucz grid interpolated for the wavelenghts adopted in U.M.A. code. Since secondary stars of Algoltype binaries normally have deep convective layers, we impose the condition that the entropy of these zones must be the same in the irradiated and in the non-irradiated models.

QS Aql is an eclipsing- and a (probably double-lined) spectroscopic binary with a period of 2.5133 days. However, from 1962 to 1968 the period was 2.5134 days. QS Aql is part of the visual double star Kui 93 with mA = 6.5 mag and mB = 6.7 mag or lA:lB = 1.2:1 (0). The system is also detected in X-rays (White & Marshall, 1983).

Binaries in clusters are particularly important: If unevolved, they may provide a check of the mass predicted for the point on the cluster Isochrone where they are found. If mass-exchange has occurred, the age and chemical abundance inferred from other cluster stars provide useful boundary conditions for theoretical models of binary evolution involving mass exchange. With these goals in mind, we have studied the early-type (B2+B6), 3.7-day eclipsing binary BF Cen in the young cluster NGC 3766.

RS Vul (HD 180939, VMax =7.0, B5V+G1III) is a semi-detached eclipsing binary with a period of 4.4776635 days. High signal-to-noise (S/N ≃ 100) spectra have been obtained with the 1.2m telescope and coudé Reticon spectrograph of the Dominion Astrophysical Observatory. The FeI 4045Å, 4227Å (blend of CaI, FeI and TiII) lines and G-band (4300Å) of the secondary are weakly visible on the spectra. Radial velocities measured from the spectra using a digital cross-correlation technique (Hill, 1982) have been used to compute a new spectroscopic orbit for the system. The primary and secondary semi-amplitudes are 54.0 ± 1.0 kms−1 and 204 ± 2 kms−1 respectively, assuming a circular orbit. The primary and secondary orbits are “decoupled” in the sense that velocities for the components can be measured separately on the same spectrum by using B5V and GOV template spectra. The secondary semi-amplitude is 17% larger than that found by Popper (1982), but the mass ratio (3.7) is identical to that found by Hutchings and Hill (1971).

Recent theories of the origin and evolution of contact binaries suggest that the two stars evolve into contact through angular momentum loss (AML; Mochnacki 1981, Vilhu 1982). When in contact, the system then evolves toward smaller mass ratio through mass transfer from the secondary to the primary component (Webbink 1976, Rahunen and Vilhu 1982). Most contact binaries have mass ratios of 0.3 to 0.5.

Some preliminary results are given of a cooperative investigation of the highly interesting radio object RY Set. From spectroscopic data the mass-ratio was found to be q=m2/m1 ≈ 3.3. An attempt to determine the helium content by model-atmosphere techniques has shown that the atmosphere of the primary component has a large helium excess; the star has every characteristic of a helium star formed by mass exchange in case B. The analysis suggests that RY Set may offer a rare chance to observe a massive system at the stage when "switching of the roles" is complete and a helium remnant with a hydrogen shell is beginning to develop the characteristics of a WR-star.

RZ Eridani is an eclipsing binary star with Algol-type light curve of rather long period of 39.28 days. As this star exhibits emission lines of Ca 11 H and K it was classified also as RS CVn type. RZ Eri has been occasionally observed with the GENEVA photometric system with 40cm and later 70cm Swiss telescope at La Silla, Chile, since 1977 mainly for obtaining a complete light curve and for detecting the secondary minimum. The observation showed, that the brightness outside minima really varies as the RS CVn stars usually do. The secondary minimum has been detected at the phase 0.67. Apart from that, the variation of the brightness outside the minima occasionally drops for a short time (about one day or even less). These drops may be due to rotation and uneven distribution of active regions on the surface of the secondary or by the gas streams between the two components. The variation of the light outside minima is certainly not caused by the primary component, because such jumps in the brightness were detected during the total eclipse, when the primary component is not visible. This star certainly deserves more both photometric and spectroscopic attention. Preliminary search for periodicities by G. Burki showed that apart from the orbital period no other periods within the range of days are present. Further details will be published later elsewhere.

Photoelectric (UBV) observations were made with the 91-cm telescope of McDonald Observatory of CI Aur (P=lḍ870) and AQ Tau (P=lḍ216) from November 1984 to January 1985. The light-curves showed obvious disturbances, including apparent "flickering", but do not appear to show secondary minima. There is a "dip" in each light-curve near phase 0P1. Average values of the colour indices outside eclipse were (B-V)=0ṃ860, (U-B)=0ṃ432 for CI Aur and 1ṃ15 and 0ṃ59 , respectively, for AQ Tau. During eclipse, CI Aur is redder.

From analysis of the photometric ellipticity effect in seven well-understood detached close binary systems, empirical values of the exponent α of gravity-darkening have been practically deduced for eleven main-sequence components of spectral types A, F and G which should cover the range of structural change (from radiative to convective) in stellar atmospheres. The result indicate that values of the exponent diminish gradually with decreasing effective temperatures from α ~ 1.0 for radiative atmospheres with T > 8500 K to α =0.2 ~ 0.3 for convective atmospheres with T < 6500 K, in spite of some uncertainty in the reflection correction process.

Spectroscopic observations were performed of the early-type contact binary AW Lac with an image-intensified coude spectrograph of 1.9−m telescope at the Okayama Astro-physical Observatory. A total of twenty-two spectra covering blue region with a dispersion of 16 Amm−1 have been secured on Kodak IIa-O baked plates. In every spectra sharp interstellar Call H,K lines are clearly seen. The spectral type of AW Lac has been estimated as early B, which substantially confirms the one adopted in the photometric analysis by Jiang et al. (1983) and is diffrent from A0 listed in General Catalogue of Variable Stars (Kholopov et al. 1985). Contrary to the suggestion by the photometric solution of Jiang et al., no definite secondary lines could be separated, though some indications of light contamination due to the secondary component are surely observed. This would imply that the light ratio of the components should be somewhat smaller than that derived by photometric analysis. No emission features appeared either. The measurement of radial velocities of the primary component for the orbital elements was made for twenty spectra by a conventional method. It was difficult to measure the radial velocities because the lines are quite broadened and deformed. Hence the measured values for the radial velocities should be regarded as rather preliminary. The derived spectroscopic elements, combined with the photometric data, give the absolute dimensions of the system for each assumed mass ratio q. For q = 1, being the adopted photometric solution by Jiang et al., we obtain too small value for the primary’s mass, comparing with its spectral type. For the mass ratio as small as q = 0.6, we can obtain a reasonable value for the mass of the primary. However, in order to get more definite conclusion the cross-correlation method would be more appropriate for the spectroscopic analysis of this system.

Observations of U Cephei made by C. M. Huffer, et al, in 1950-51 and in 1959, are presented here to contrast with other observations made by Huffer and others.

In many cases, to see a light-curve of an eclipsing binary is to see all light-curves for that particular system. This is certainly not true of U Cephei which, because of its rapid variations, has held the attention of so many for so long.

The 1950-51 yellow and blue observations were made at Washburn Observatory, Madison. The data have been transcribed from Huffer’s note books to a floppy disk and are available.

V718 Sco (HD 145718 = SAO 184232) is an eclipsing-binary system with an orbital period of about 200d, depth of primary minimum about lṃ4 and a primary component of spectral type A2 (Wood et al., 1980). Neither period nor eclipse depth are well determined and the system has not been observed photoelectrically. The IRAS point-source catalogue (Beichman et al., 1985) contains an object having a far-infrared excess at a position closely agreeing with that given for V718 Scorpii in the S.A.0. catalogue. The fluxes (in Janskys) at 12 µm, 25 µm, 60 µm and 100 µm are 5.73, 5.92, 4.91, 3.37 respectively and this distribution suggests that V718 Sco is surrounded by a dust envelope in which there is a temperature gradient. From the ratios of the fluxes, a dust temperature of about 140 K is found; the fluxes at 60 μm and 100 μm would suggest a lower temperature.

Photoelectric observations of the long period RS CVn type eclipsing binary RZ Eridani were made with the 1.2m reflecting telescope of the Japal – Rangapur Observatory during the observing seasons 1976-79. We could not obtain a full light curve in any one season and therefore the combined light curve is used for analysis. No distortion wave was found in this system. The period of the system (39ḍ282466) is found to be constant during the period 1906 to 1979. From W-D solution we obtained the eccentricity to be zero whereas Popper (private communication) from his spectroscopie studies, suggested a value of e = 0.339 for the eccentricity. Such disagreement between the photometric & spectroscopic eccentricity values is reported in the system SX Cas (Struve 1944 Ap.J, 99, 89., Shao 1967 A.J, 72, 480). This might be due to circumstellar matter covering the whole system. The ultraviolet excess found by us in RZ Eri is similar to that found in systems like SX Cas, RX Cas, βLyr & W Ser

We studied the circumstellar gas in Algol (β Persei) by analysing Hαdifference profiles (observed profiles minus composite theoretical (LTE) photospheric absorption line profiles of the stars), at 98 phases in the binary’s orbit (cf. Richards 1986, Ph.D. thesis, University of Toronto). The data were obtained from Sept. 1976 to Dec. 1977; with an average phase interval of 0.02 over the entire orbit.

There was a smooth change in the profiles from strong, redshifted emission just outside primary eclipse, to an almost flat profile at mid-secondary eclipse, to strong, blueshifted emission just before primary eclipse began. Absorption was detected throughout primary eclipse, and there were smooth transitions between pure absorption and pure emission. The emission and absorption had FWHM’s of ~200 km s−1 and ~200 to 450 km s−1, respectively; with line strengths up to 10% and 19% of the continuum, respectively.

Unpublished photoelectric observations of the systems BX And and RR Lep were subjected to light curve analysis using the Wilson-Devinney Code.

The short-period eclipsing binary system BX And was observed on five nights in 1976 at the Morgan-Monroe station of the Goethe Link Observatory of Indiana University. The observations covering the eclipse portions of the light curves yielded four times of minimum light. A period study covering 89 years of observations confirms that a major period change took place about 1950. The system is suspected of being quite active on a short time scale. Standard magnitudes were derived for BX And and for the comparison star. The corrected color indices indicate that BX And and the comparison star BD+39° 476 are in the spectral range of F3-F5. The light curves, defined by 1092 observations in B, 1097 in V and 971 in the U filter are symmetric. The difference in the eclipse depths are quite large averaging 0.m46. A distinct de-reddening of the light curves occurs during the secondary eclipse. The first synthetic light curve solutions of the system were obtained. The solution of BX And indicates that the system consists of an F-type primary and a K-type secondary component in a state of shallow contact. This result is supported by the location of BX And on the Eggen period-color diagram for contact binaries. The large mass ratio, temperature disparity and period increase are found to be consistent with an early contact phase of thermal relaxation oscillations.

We investigated the effect of mass accretion on the secondary components in close binomy systems (Mtotal ≤ 2.5M⊙M2.0 ≤ 0.75M⊙) exchanging mass in the case A.

In recent years, we have been studying the energy distribution of RS CVn binaries from UV to far IR wave lengths, in order to derive general properties of the systems and to better understand their evolutionary scenario, including the history of mass loss (Busso et al., 1987, 1988). In this framework, we have so far analyzed, at different level of accuracy, a total of about 60 sources, among which 30 have been the object of detailed studies, on the basis of broad band photomertic observations from 0.35 to 60 µm, using ground-based telescopes (mainly at La Silla, ESO) and IRAS-PSC information. For these 30 binaries, the quasi-periodic variations due to the presence of photospheric spots have been carefully subtracted, to derive the energy distributions of the unperturbed systems.