Referring to the “promise” of something is likely to imply that little has been accomplished. This is not true in the present case however. In optical interferometry, for example, there has been a steady development during the last decade or so after somewhat of a lapse subsequent to Michelson and Pease’s work some 65 years ago. Most of the work to date, however, has been directed towards the measurement of stellar diameters and binary stars and is hence not germane to the present topic of reference frames. What is required for the latter is the analog of the phase coherent interferometers used with such conspicuous success in radio interferometry. The important point is that such analogs are now available in both the optical and infrared (10u) wavelength regions.

The order of magnitude of relativistic effects is expressed as the power of v/c where v is a typical speed of objects and c is the speed of light in vacuum. In the neighbourhood of the Earth, v ≅ 30 km/s. Then the magnitudes of the relativistic effects are ordered as follows:

New observations of the long period eclipsing system Epsilon Aurigae are discussed, including optical and infrared photometry, ultraviolet spectrophotometry and optical polarization. Trends are noted in the light curves and compared to previous eclipses. Comments regarding interpretation are also provided.

Spectroscopic observations from the ultraviolet, visible, and infrared obtained at the recent eclipse are discussed. The rotation curve for the disk around the secondary suggests that secondary is a low mass star (or binary). This result with the known mass function suggests that the primary may be a low mass (m1 ≤ the Chandraskehar limit, 1.4 M⊙) star leaving the AGB and evolving to the white dwarf region.

Various interpretations of the data of Epsilon Aurigae had been proposed before the recent eclipse. Every model explains the observations to a certain extent, but simultaneously disagrees with some other aspects of the nature of this system. During the 1982-84 eclipse, observations extending from far UV to IR have been carried out. A lot of data have been obtained and discussed in the workshop held at Arizona on this January. The spectroscopy and the photometry in visual region, however, are still important particularly to get informations about dynamical features of the components. In this review we present several interpretations mainly using new data obtained from ground-based spectroscopic observations including ours.

The ultraviolet observations of four Zeta Aurigau stars are reviewed. A, probably oversimplified, interpretation of the observations points to a straight forward connection between the spectral type of the B star and the amount of high temperature plasma in the systems.

In the context of the Joint Discussion, it is clear that by “long period binaries” we understand the system of ∊ Aurigae and the ζ Aurigae systems. The question is, then, how to determine which systems could be considered “related” to those long period ones.

In the earliest studies of close binary evolution (Paczynski 1967; Kippenhahn, Kohl, and Weigert 1967; Plavec, et al. 1968), it was assumed that the total mass and orbital angular momentum of a binary system are conserved during mass transfer. This assumption of convenience actually succeeds quite well in producing model post-mass-transfer binaries which closely resemble classical Algol-type systems, and helium-star binaries such as KS Per and u Sgr as well (Plavec 1973; Schonberner and Drilling 1983). Among longer-period interacting binaries, however, there are strong reasons to believe that these simple assumptions break down. For example, it is well-known that single stars may lose a very substantial fraction of their mass in a stellar wind during ascent of the giant and asymptotic-giant branches (e.g., Kudritzki and Reimers 1978). In addition, many highly-evolved short-period binaries, such as the cataclysmic variables, appear to owe their origins to very long-period progenitors (Paczynski 1976; Ritter 1976; Webbink 1976). These latter systems evidently evolved through a common envelope phase (Paczynski 1976; Meyer and Meyer-Hofmeister 1979), in which the giant progenitor of the present white dwarf devoured its companion star, and ultimately was divested of its envelope by the release of orbital energy as that companion spiralled toward its core.

Recent observations of the class of objects called symbiotic nova are reviewed. They are suggested to be widely-separated long-period binary systems undergoing mass exchange by wind accretion. Their radio, infrared, optical and X-ray properties are explained by a model of interacting winds.

Notes made during the presentations of Joint Discussion II have been distilled into the interpretation of this summary.

A sample of high-dispersion optical spectrograms of ε Aur,taken on different epochs before and during eclipse, has been processed by computer in order to extract the shell spectrum, produced by the eclipsing body. Using an uneclipsed spectrum as reference, the primary’s dominant contribution was removed, and this makes it possible for the first time to study the secondary body spectrum separately at all eclipse phases. As the first striking result, one finds that the internal regions of the extended eclipsing body are hotter than the outer zones.

It has recently been suggested (Lissauer and Backman, 1984; Eggleton and Pringle, 1985) that the secondary mass within the Epsilon Aurigae disk is not a single object but an embedded binary. Lissauer and Backman pointed out that this idea would help greatly to account for its low ratio of luminosity to mass, while Eggleton and Pringle argued in addition that the system’s evolution could be much better understood in terms of such a configuration. They also noted that a central opening in a thin disk, which was proposed by one of us (Wilson, 1971) as a means to produce certain unusual features of the eclipse, can be accounted for quite naturally if the disk has a binary at its center. With such an embedded binary, circular orbits will be impossible for particles inside a critical radius, leading to an effective viscosity which will cause disk material to spiral inward.

New provisional orbital elements are derived for δ Sge and the next conjunction in 1990 should be observed. Probably no bodily eclipse of the B-star will be seen, but an atmosheric eclipse is expected. There are mass motions in the M-star’s atmosphere.

The VV Cep close binary system (O8V + M2 lab; P = 20 3 yrs.) is described from published spectral, radial velocity, photometric, and astrometric results. A long-term photometric monitoring program shows intrinsic variability in a red bandpass. Variability exists on several time scales and the longest of these is attributed to tidal distortion of the cool supergiant by the equally massive hot companion. A theoretical “distortion” light curve, when faced against the observations, indicated the radius of the supergiant to be significantly smaller than the accepted value of ~1600R⊙. This conclusion is examined in the context of a pulse of polarized red light occurring near the time of periastron and interpreted as Roche Lobe overflow of the supergiant envelope. It is shown that the photometric and polarimetrie results may be made accordant, not by appeal to a very large level of scattered red light, but rather by invoking the loss of constraint originally imposed by the Roche Lobe geometry.

The system parameters of the ζ Aur-type binaries, all containing a cool supergiant and a hot dwarf, have been improved recently by IUE observations (N.P. Schroeder, 1985; A.Ap.147, 103). But the diameters of the supergiant components, determined with different indirect methods, are still discordant. We attempted to solve such discrepancies by measuring directly the angular sizes of these stars, expected to be of a few milli-arcseconds.

It has been well known for some time that some close binary stars have a semidetached or contact configuration. Many late-type systems ----- W WMa systems ----- are known to have these configurations. Their dimensions are typically of solar mass to fractions of solar masses, and solar radius to fractions of solar radii. Early-type systems with semidetached and contact configurations have been found in recent years. Their typical dimensions are from several solar masses to tens of solar masses, and from several solar radii to tens of solar radii. Generally, both late and early-type close systems are located in the vicinity of ZAMS and TAMS in an H-R diagram. They are believed to be the result of case A or B mass exchange of close binary evolution. Some of us have been wondering why we do not find semidetached or contact systems with much larger dimensions consisting of supergiant stars?

We currently know of at least three distinct classes of degenerate pulsating variable stars; they occur with a practically uniform spacing in the log of the effective temperature and span nearly the full sweep of the white dwarf cooling sequence in the H-R diagram. The hottest of these variable stars are the pulsating PG 1159-035 stars. Extremely hot, compact, stars, they appear to be contracting and cooling on their way to becoming white dwarf stars. These proto-white dwarfs have photometric properties similar to the pulsating white dwarf stars, and are reviewed separately in these proceedings by A. N. Cox. The two remaining classes of compact pulsating variables are found in relatively narrow instability strips occupying distinct portions of the white dwarf cooling sequence after the constant radius, purely cooling, phase has been reached. These two classes of variable stars are the topic of this review. In this work I will use the concise notation introduced by Sion et al. (1983) to indicate the two classes of variables: the ZZ Ceti’s, and the pulsating DB white dwarfs, become simply the DAV, and the DBV stars, respectively.

The PG1159 variables, named after the variable of that number in the Palomar-Green blue star catalogue, have high luminoisites, high surface temperatures, and high gravities. Their masses, however, must be the normal low value of 0.6 solar mass because they are the direct antecedents of the classical DB white dwarfs. In every case, they seem to have no hydrogen at all in their atmospheres, but significant helium, carbon, and oxygen is present (Sion, Liebert, and Starrfield 1985). Table 1 gives a list of these stars of which most, but not all, show light variations indicative of nonradial low degree, but probably high order, g modes.

The present state of our knowledge of non-radial oscillations in δ Scuti stars and Rapidly Oscillating Ap stars is discussed primarily from an observational point of view. For the δ Scuti stars the need for complete frequency solutions for multi-periodic non-radial oscillating stars is emphasized in order for stellar seismology of these stars to be possible. An introduction to the Rapidly Oscillating Ap stars is given along with reference to a more complete recent review of those stars.