In this work we suggest one possible approach to “computerization” of the process of the visual double star orbit determination. Our computer program, based on the original method (Olević 1989), is interactive which means that the calculator of the orbit makes the final decision about the choice of the best orbit.

Based on Docobo’s method for the calculation of orbits of visual binaries, an algorithm is presented for the calculation of short-period orbits when observational data comprise radial velocities and polar coordinates. The method is applied to some examples.

The method of perturbations of Deprit has been applied to the stellar three-body problem. The calculation, developed previously by the authors in other articles, is here systematicized for easy use and applied to various triple systems.

The increasing use of CCD’s and IRCCD’s to detect stellar companions, either by direct imaging or speckle techniques, raises the issue of the fraction of companions whose instantaneous, projected separations lie in the range corresponding to the geometric limits of the detector. The issue is of especial importance to recent surveys employing IRCCD detectors of relatively very small area (projected onto the sky). The distribution of observed separations reflects not only that of orbital semi-major axes, but also distributions of distances to binary systems, orbital eccentricities, tilt of orbital planes with respect to the plane of the sky, and of arguments of periastron. Proper inference of, e.g., binary multiplicity requires estimates of completeness that should incorporate contributions from all these factors.

For stars fainter than Mv ≈ 6 the density distribution perpendicular to the Galactic midplane can be approximated by an exponential fall-off with a scale height of about 270 pc. We show that even if in fact constant an apparent decrease of the scale height to about 150 pc for stars with Mv ≈ 17 can be expected if all ‘stars’ measured in the photographic surveys are unresolved binaries. In principle measurements of the apparent scale-height allow the study of the mass-ratio distribution and the proportion among ‘stars’ of binary systems.

In open clusters the scatter about the single-star main sequence is usually negligible. However, unresolved binary systems are brighter and redder than single stars, and thus some ‘stars’ appear shifted away from the main sequence. We make very simple models of the Praesepe cluster, and find evidence that low-mass systems prefer independent component masses, whereas systems of higher mass than the sun appear to favour some correlation towards equal-mass components.

If all stars within a small volume surrounding the sun are counted we obtain an approximation of the low-mass single-star luminosity function. Alternatively, deep photographic surveys cannot resolve most of the binary systems, and consequently we obtain an approximation to the system luminosity function. Comparing the single-star and system luminosity functions we derive the stellar mass function and constrain the properties of binary systems.

From an initial value of the period and a fitted curve for the radial velocities an homotetic plane to that of the relative orbit is constructed from which i, Ω and parallax are deduced. The remaining orbital elements are obtained from the relations of the elliptical motion.

About 40% of potential OH / IR stars, color selected from the IRAS Point Source Catalog, have no 1612 MHz masers. While these objects are rarely carbon rich, they are usually associated with circumstellar shells. The natural explanation for these “OH / IR star color mimics” is that they are systems with a degenerate companion collecting an accretion disk from a red giant wind. This provides them with an extra source of UV for dissociating their molecules. The persistent absence of the usual complement of masers from an O-rich shell is then a pointer to the presence of a degenerate companion. These occur in association with ~45% of old giant stars.

It has long been recognized that tidal interaction between the components of close binaries will tend to circularize their orbits (e.g., Darwin 1879; Zahn 1977). In fact observations show an abundance of circular orbits in binaries with periods of days. However, the dissipation mechanism required for circularization, the timescales involved, and the dependence on period, mass, evolutionary state, and initial eccentricity of the system remain subjects of debate.

Circularization theories such as Zahn (1977) state that circularization in binaries where at least one component possesses a convective envelope is much more efficient than in binaries where both stars have radiative envelopes. Giuiricin et al. (1984; GMM) studied the period-eccentricity distribution of O-, B- and A-type binaries and argued that the observations were consistent with Zahn’s theory for radiative envelopes. But recently, Tassoul (1988) has presented an alternative circularization theory with similarly efficient circularization in radiative- and convective-envelope binaries. In addition, period-eccentricity distributions for many samples of main-sequence convective-envelope binaries are now available. Here we reconsider the observed short-period eccentricity distribution of radiative-envelope binaries in light of these new observations and theory. Specifically, we investigate the period-eccentricity distribution of a sample of binaries with A-type primary stars.

In a double or a multiple system, in which one of the components is a pulsating star, the light-time effect leads to apparent changes of the pulsation period. In some cases, one can obtain much more accurate values of the spectroscopic elements from the fit to the 0 — C diagram than from classical analysis of the radial-velocity data. In addition, in the analysis of the O — C diagram, photometric observations can be used. They are easy to obtain, and therefore are usually more numerous than the spectrographic ones.

Below we present the results of a study of three stellar systems, in which the light-time effect is observed. Primaries in all these systems are β Cephei-type pulsating variables.

We study a sample of 123 wide visual double stars for which astrophysical parameters are at least partly available from uvby Hβ photometry. All of these have components brighter than 10 mags and a component angular separation between 10 and 20 arcseconds.

We find that at least one third of them are optical; for relative proper motion (RPM) pairs this fraction is 60% or even more. These results are in fair agreement with the predictions we formulated in an earlier paper on the basis of a statistical criterion.

The light-time effect and the phase jump in the pulsation period of Cepheids as two characteristic manifestations of duplicity are discussed.

The European Southern Observatory gives opportunity to the European astronomical community to use a large variety of instruments. In this paper we try to make an assessment about the proposals that show an interest in visual binary and multiple star research. The material is based on projects proposed and performed in the last 3 years. Main streams of research are: speckle measurements, radial velocities, photometry (completion of catalogues), and astrometric positions.

1. I. We recall the main surveys: J. Herschel (1826), W. Struve (1825), A.W. Burnham and G.W. Hough (1880), R.G. Aitken and W.J. Hussey (1910), R. Jonckeere and T.E. Espin (1910), W.H. van den Bos (1925), R.A. Rossiter (1950). Presently the classical surveys are continuing with P. Muller, W.D. Heintz, and P. Couteau. The interferometric survey with large telescopes is carried out at CHARA.

2. II. The results of old surveys, up to 1950, amount to 700 known orbits out of more than 35000 found binaries. The new surveys since 1965, both visual and interferometric, had checked 4000 new binaries giving already about 30 orbits. The periods are shorter and shorter: the mean period is 200 years for Struve (1825) binaries, 75 years for Aitken’s (1910), 25 years for Couteau and Muller’s (1970), and 7 years for CHARA’s. The number of known orbits increases exponentially with time.

3. III. The “classical” surveys will have to be performed again within fifty years with refractors.

   The interferometric and aperture syntheses surveys will be able to observe every binary, even those in contact with each other. With HIPPARCOS’ results, astronomers will dispose of a complete set of data for new theories of stellar evolution.

Following the diversified topic of this conference, let me present a variety of comments — not all new, but resulting from a long string of stars drifting across the desk. The chase after visual orbital elements is not exactly a self-purpose but is aiming at further data, in particular, at good masses. The last published lists of high-quality mass determination represent the status of 20 years ago; but a compilation at this time would probably not last long as the progress promises to quicken.

We have 1000 positional (visual/photographic/speckle) orbits, among them about 700 acceptable in the range from fair to definitive. Yet less than 10% of them give good component masses. Most of them are outside the range of parallax measures with the requisite, high precision (that unfortunatly holds for the Hyades); some frustrate the parallax measurer by displaying wedge– and peanut–shaped images, and the more exciting cases of abnormal, non-main–sequence components often cannot get good mass ratios owing to large distances or long periods.

The calibration of luminosities using trigonometric parallaxes introduces well-known errors that are a function of the ratio of the parallax error to the parallax, when the sample is chosen from stars with measured parallaxes larger than some minimum parallax. In this paper it is shown that similar errors are also introduced into the mass axis of the mass-luminosity relation (MLR) and can result in a biased MLR. The bias is shown to be related to the Lutz-Kelker correction to the absolute magnitude, as extended by Hanson for the case of selection effects in the data sample. The size of the correction in the mass axis is substantial and for the case of a uniform distribution in space, it can amount to a multiplicative factor of 1.17 in the mass for a ten sigma (σ/π = 0.10) parallax and a factor of 1.62 for a five sigma (σ/π = 0.20) parallax.

The first lists of visual double stars were published by Mayer and Herschel in the late 18th century, but only sporadic lists and catalogs appeared during most of the following century, until Burnham began the systematic collection of such data, which has continued to this day. This contribution discusses the evolution of the visual double star data base over the last centuries and suggests how the data might be ordered to serve future needs.

A large collection of machine–readable catalogs containing data for various types of double– and multiple–star systems has become available over the last decade or so. These catalogs can be divided logically into general compilations of multiple–star data for visual systems and other collections of information for particular classes of binaries, such as cataclysmic, eclipsing, interferometric, spectroscopic, etc. A few large databases containing double– and multiple–star data have also become accessible over the last few years. This paper gives a general overview of some of the more important machine–readable catalogs and databases available, and includes a brief description of the information that each contains. The potential for what can become available in the near future, just by incorporating current information into a system providing full data retrieval, is also discussed.

No modern catalogue of wide binary and multiple systems (WBMS) exists for the region of the solar vicinity (stars nearer than ~22 pc), that include updated information on their membership to moving clusters and an age classification. With the aim of filling this gap, and also because of its importance for investigating the dynamical evolution of double and multiple systems, we have compiled a WBMS list extracted from the catalogues of nearby stars of Gliese (1969, also Gliese & Jahreiss 1979), as well as Luyten’s NLTT (Luyten 1979–1980, Luyten & Hughes 1980, see also Warren et al. 1989), the Bright Star Catalogue (Hoffleit 1982), the catalogue of Woolley et al. (1970) and other sources.

By comparing the transverse velocities of WBM systems with those expected for members of the Hyades and Sirius Superclusters, membership of some WBMS to them has been established. We have classified as probably young systems (PYS) those with one component satisfying at least one of various criteria of youth. A system that is not a PYS is classified as probably old (POS).

The catalogue contains 385 binaries and 85 systems of higher multiplicity. Out of these, 129 binaries are PYS and 256 are POS, while 32 multiples are PYS and 53 are POS.