La dÉcouverte des Étoiles doubles visuelles a ÉtÉ une des consÉquences logiques du developpement de I'astromÉtrie Équatoriale. L'Étude de ces objets est fonction du temps et de l'abondance des dÉcouvertes qui dÉpend, elle aussi, du temps. II en rÉsulte que nos connaissances dans ce domaine croissent en progression arithmÉtique, au lieu de suivre une progression gÉomÉtrique comme la plupart des spÉcialites astrophysiques qui dÉpendent davantage de mÉthodes que du temps.

If we may judge by the number of eulogistic review articles to which it gave rise, one of the main talking points among astronomers in the early nineteen-twenties was undoubtedly the application of the interferometer to optical astronomy. It was only natural that interest was focused mainly on the brilliant success of Michelson and Pease (1921} in measuring stellar diameters with the 20-ft beam interferometer on the 100-in Mount Wilson reflector.

A new photoelectric area scanner, designed primarily for observations of double stars, has been put into routine use at the Lowell Observatory. A description of the scanner and of the associated data acquisition system is given. The procedure of measuring the relative positions of double star components is described and the accuracy obtainable by this method is discussed. This contribution and a subsequent one (p. 170) will appear jointly under the title 'A Photoelectric Area Scanner for Astrometry and Photometry of Double Stars' in Lowell Observatory Bulletin No. 154. This work has been supported by National Science Foundation Grant GP-6983.

A photoelectric scanning photometer is being tested at the 60 cm-refractor in Hamburg in order to measure visual binaries. The data-acquisition is accomplished by a small on-line computer PDP-8/S which samples data from three photon-counters connected to three narrow slits in the focal plane.

A preliminary investigation of the image profile as it is obtained from the adding of many scans of a star on top of each other shows that about 80% of the light is concentrated in a Gaussian core with σ = 1"-2" whereas the rest goes into non-Gaussian wings. The deviation of the profile from a single Gaussian is most pronounced in good seeing.

When a star is occulted by the dark limb of the Moon its apparent intensity drops to zero very quickly. MacMahon (1909) proposed that the time of disappearance would measure the diameter of the star, but Eddington (1909) demonstrated that diffraction effects at the lunar limb would lengthen the apparent time of disappearance to about 20 msec, and suggested that these effects would greatly limit the usefulness of the technique.

Progress in the study of visual binaries depends upon the existence of a series of astrometric observations in addition to observations of their relative motions. The present paper discusses the proper motions, parallaxes and mass-ratios of visual binaries, the detection of astrometric binaries and the photographic astrometry of faint binaries.

The proper Motion Survey with the 48-in Schmidt telescope has now progressed far enough such that we may begin to make some meaningful statistical discussions of the results obtained. Altogether 135 regions have been blinked - one seventh of the total - and in particular all fifty plates covering the area of the North Polar Cap, north of declination +69 (1855) have been blinked and completely measured.

L'observatoire de Poulkovo a publie dans plusieurs mémoires les mouvements propres des 50000 étoiles jusqu'á la 15-me grandeur photographique obtenus par l'astrographe de la Carte du Ciel. Dans la présente étude nous avons utilisé 74 aires de Kapteyn [1, 2] et 25 autres aires ayant au centre les amas stellaires, les nébuleuses planétaires, les Novae etc [3, 4, 5, 6, 7, 8].

Les travaux sur les parallaxes dynamiques sont peu nombreux; les plus rÉcents remontent dÉjá loin dans le passÉ (Russell et Moore, 1940; Barbier, 1936; Baize et Romani, 1946; et Strand, 1953). L'idÉe directrice est toujours la même: associer la troisieme loi de Kepler et une relation masse-luminosité.

En 1961, au cours du Symposium IAU sur ce même sujet, M. Rosch avait déjá annoncé l'intérêt que pourrait présenter l'utilisation d'un convertisseur d'image de type Lallemand pour la photographie des étoiles doubles. Des essais prometteurs avaient deja ete faits sur le rêfracteur de 60 cm du Pic-du-Midi.

J'ai été conduit á m'intéresser á la mesure des étoiles doubles au cours d'un projet de mesures spatiales de positions d'étoiles par une méthode de balayage photoelectrique. L'existence d'etoiles doubles perturbe les mesures. J'ai done étudié les limitations imposées aux mesures de position par balayage d'images du fait de composantes d'etoiles doubles. Cette étude m'a donné I'occasion de réfléchir au problème de la mesure des étoiles doubles et voici le résultat de mes réflexions.

Le concours de diverses techniques d'observation a toujours été profitable au progrès des connaissances astronomiques.

Dans le cas des couples stellaires, l'observation visuelle et Fobservation spectroscopique se completent heureusement: chacune d'elles - lorsqu'elles sont possiblesconduit a la connaissance des éléments orbitaux, sauf que la première ne fournit pas l'échelle de Forbite en unités astronomiques et laisse subsister une certaine indetermination, relative á la position du noeud ascendant, et que la seconde n'apporte aucune information sur la valeur de Finclinaison et sur celle de Fangle de position de la ligne des nœuds.

The value obtained for the difference in radial velocity between components of a visual binary that is unresolved on the spectrograph slit appears to depend, sometimes, on whether the measurement is made visually with a microscope or by means of an oscilloscopic setting device. This apparent dependence has been confirmed by measurement of artificially produced doublelined spectrograms, and disappears for line pairs separated by more than 1.5 or 2 times the half-widths of their components. The dependence arises from blending of the two line profiles. There is some evidence that the results obtained from visual measures are affected by the scale of the image being measured. For this reason, oscilloscope measures are probably to be preferred; although their errors are sometimes larger, they seem to be more consistent. Errors arising from this sort of blending are not sufficient to explain measures of relative radial velocity of the components of some visual binaries, that differ widely from the predictions made from the visual orbits.

There are certain visual double stars which, when close to a node of their relative orbit, should have enough radial velocity difference (10-20 km/s) that the spectra of the two component stars will appear resolved on high-dispersion spectrograms (5 Å/mm or less) obtainable by use of modern coude and solar spectrographs on bright stars. Both star images are then recorded simultaneously on the spectrograph slit, so that two stellar components will appear on each spectrogram.

The use of a coudé spectrograph for securing the high-resolution spectrograms necessary to follow the slow variations of radial velocity exhibited by visual binaries is discussed. Recent observations, using the spectrograph at the coudé focus of the Dominion Astrophysical Observatory's 48-in. reflector, are then presented for the systems of α UMa, ε Hya, β LMi and γ Leo.

It is necessary to have quantitative estimates of the intensity of lines (both absorption and emission) to obtain the physical parameters of the atmosphere of components.

Some years ago at the Crimean observatory we began the spectroscopic investigation of close binary systems of the early spectral type with components WR, Of, O, B to try and obtain more quantitative information from the study of the spectra of the components.

Astronomical observation frequently is focused on minute quantities, and on digging information even from below the 'noise level'. In all cases of long-term variations, such as visual binary motions, measurements over a long time interval have to be combined. All of this requires a knowledge of the observational errors in the past and present. We usually are not at liberty to discard old observations since we cannot repeat them at any later time desired. Visual observations leave no re-measurable records, so we have to take the word of the observer, and make the best of it.

Au cours de recherches bibliographiques diverses, nous avons remarqué que bien des observateurs se sont servis et se servent encore de formules par trop approximatives pour calculer - lorsqu'ils le font - les erreurs moyennes affectant leurs mesures

Soit Δt, Fintervalle de temps couvert par les observations ayant permis le calcul des éléments orbitaux d'une étoile double visuelle. Soient P, sa période et a", son demigrand axe.