The Carlsberg Automatic Meridian Circle (CAMC) has been operating on the island of La Palma since 1984. Since that time it has made more than 500,000 observations of stars and minor planets. Observation are made by accumulating the output from a series of scans by a pair of 4″ wide slits which oscillate back and forwards across the star as it traverses the meridian (Helmer et al. 1991). The error of a single determination of a star position is 0″.14 in RA and Dec and 0.05 in V magnitude. For 20 observations, the errors of a mean position are reduced to about 0″.05.

Trapezia systems are defined as multiple stars, having three or more components with separation ratios in the range 0.3 to 3. The revival of interest in Trapezia is due to their potential astrophysical significance, as they could originate from a single protostar and be in an expansion stage because of their possible positive energy (see, for example, Bernacca 1988 and references therein). Further decisive advancements in understanding the nature of these systems require data for establishing a list of physically bound systems as well as for the systematic study of their kinematics and energetics. In the present progress report we test three representative cases with the combined exploitation of astrometric, photometric, and spectroscopic data.

Using a short exposure, one dimensional area scanner, a programme of photometry on binary stars with separations <10″ has been initiated; using speckle techniques, photometry of binaries with separations <1″ is possible. We describe the equipment and techniques and present results acquired during commissioning.

We have examined the visual and speckle observations of visual double stars made by 31 experienced observers in order to evaluate possible systematic errors in these series. Using 57 “definitive” orbits, we find no appreciable errors in position angle. We do find systematic effects in separation for some observers, and, in particular, a “proximity” effect for measurements of pairs closer than 0″.5.

Root-mean-square residuals are:

We have obtained CCD photometry of the classical Cepheid FF Aql and the companion 6″ away to determine whether they are likely to be physically associated. Because the Cepheid is 5 magnitudes brighter than the companion, the measurements are difficult. The values we find for the companion are V = 11.14 ± 0.07 mag, B – V = 0.60 ± 0.05 mag and V – R = 0.39 ± 0.04 mag. If the companion were at the same distance as the Cepheid, its absolute magnitude would be MV = 2.58 mag, corresponding a spectral type of approximately A8 V. The observed (B – V)0 corresponds to a spectral type of F4 V to F5 V. The observed color and spectral type are incompatible with a ZAMS magnitude of the companion at the distance of the Cepheid.

Positional measures indicate that there may be relative motion between the two stars, which would be too large to be orbital motion. We conclude that the 6″.8 companion is not a member of the FF Aql system. Information about the four stars in the direction of FF Aql is summarized.

We present first results of a catalogue of standard double stars for the astrometric calibration of CCD’s. The data were taken from photographically determined precise positions and proper motions of stars in the region of radio sources and open clusters. In this report, we give preliminary results of stars in the region of 3C 273 and NGC 1647.

The only reason that comes to mind why ‘visual’ binaries (whether discovered visually or not) conventionally receive discoverers’ designations, whereas spectroscopic ones do not, is that many visual binaries were discovered before most of the stars concerned had any other designations; spectroscopic binaries were not invented until after the B.D. was published. It is accordingly suggested, very gently, that it no longer serves a useful purpose to attach additional identification numbers to stars that are already well known, and it could even be argued that unnecessary proliferation of designations is best avoided.

Zeta Cancri is a multiple system in which the well-observed orbit is an inner, or close one. Three-body coupling effects are an order of magnitude more significant for the close orbit in a hierarchical system, and they must be included. An exact numerical integration is very easy and requires no approximations. Inclusion of these effects improves the residuals for this system.

New parallax and orbital period estimates for the astrometric binary BD +6° 398 are presented. The mass of the unseen companion is discussed.

The key formulae of the AMP–method for deriving the orbital elements of wide visual double stars are considered. The usual astrometrical observational data must be supplemented with the values of radius of curvature of observed arc of the binary, its trigonometric parallax and the astrophysical data: the sum of the mass of the components and their relative radial velocity. Thus, the orbital elements can be derived on the basis of short–arc observations.

The orbit of the visual double star ADS 48 AB is determined on the basis of Pulkovo and Washington sets of observations. The similar deviations in observations of the both sets are discovered. It may be explained by the existence of the invisible satellite with a mass about 0.0lM⊙.

V448 Cyg (HD 190967 = BD+34°3871) represents rather an uncommon case, where the primary component (indicated by stronger lines in the combined spectrum) is the star exhibiting mass loss. The system has a circumstellar envelope, formed by mass flow from a primary component filling its Roche lobe, and by a stellar wind that is stimulated by the duplicity of this system of two hot stars (BO Ib + O9.5 V — see Glazunova et al. 1963). Ultraviolet, polarimetric, and spectral observations of V448 Cyg permitted us to form a model of the structure and parameters of this system’s circumstellar envelope.

We have begun a search for faint companions to cataloged G/K metal–deficient dwarfs. The main goals of this investigation are:

1. i) to collect a database of halo M-type stars

2. ii) to study the frecuency of binary separations in the range 1″ - 50″ for Population II stars

3. iii) to find some metal-poor very–cool dwarfs that may serve as references to investigate the low-mass end of the halo main sequence.

In this paper we present the first results from VRI CCD photometry of a subset (51 stars) of our sample. We have identified 7 possible very low mass companions (angular separations 1″.5 – 30″) of halo subdwarfs with [Fe/H] in the range from −0.8 to −2.6.

Complementary accurate photometric data with astrophysical content are needed for a well-chosen sample of binaries and multiple systems for which good-quality astrometric data already exist or will soon be available. The observational programme, started in the context of the European Network of Laboratories “Visual Double Stars” (Oblak et al. 1992), is therefore based on samples extracted from the “Catalogue des Composantes d’Etoiles Doubles et Multiples” (CCDM, Dommanget, 1989) and reported in Annex 1 (Double and Multiple Systems) of the HIPPARCOS Input Catalogue (C. Turon et al. 1992).

Systems with components in the HIPPARCOS Input Catalogue are selected for which the present photometric information is poor, i.e. not all components have been observed or they have colour indices and/or magnitudes of insufficient quality for extraction of astrophysical quantities (Figure 1).

Observations, performed in various observatories located in both hemispheres, must yield both classical and CCD photometric campaigns.

We study the multiplicity function and physical properties of single, double, and multiple stellar systems in the solar neighbourhood (r < 10 pc), using a new preliminary machine–readable version of the Gliese & Jahreiss Catalogue (1991).

The ratio of (n+l)-ple to n-ple systems is a constant fraction of about 1/4 for n =1, 2, 3, 4. The luminosity function f(M) for primaries in binaries has an additional peak at M є (6m,8m) that is absent in f(M) for single stars and secondary components. A significant correlation between the absolute magnitudes M1 and M2 of the components in binaries takes place.

A series of photographic observations spanning the interval 1962 – 1991 have been examined in a study of Lalande 21185, suspected to be a double or multiple object. The observed value of secular acceleration corresponds to the radial velocity of this star. The perturbations in proper motion with suspected period of 8 years have not been confirmed.

Regular photographic observations of ADS 5983 (δ Gem) with the Pulkovo 26-in refractor have been made since 1972. The series of observations over the time interval 1972-1990 are considered. New orbital elements of the binary are obtained by the AMP–method. Some wave with a period about 5 years in the orbital motion of this star is found.

We discuss the accuracy of CCD astrometry, and we present an improvement on the method used for the photometric reduction of visual double stars CCD data, whenever the angular separation of the components is only a few arcseconds.

We have performed uvby aperture photometry of wide visual double stars with G–type primaries. We chose our pairs in order to have minimum angular separation of their components 10″ and mainly less than 20″. It is shown that both components have similar photometric parameters. We infer that most of these double stars have components of common origin.

Cepheid variables are exceptionally useful objects for astrophysics and cosmology but at the same time these stars are normal as far as their duplicity is regarded. A brief summary is given on the relevant data of the known spectroscopic-binary Cepheids and other potential binary Cepheids, duplicity of which is suspected on the ground of various photometric methods.