En principe, nous parlerons des mesures d'etoiles doubles exécutées au micromètre a fils par la méthode classique des doubles distances, mais il va de soi que la plupart des considerations relatives aux erreurs peuvent être étendues aux autres precédés.

The long range program of the Sproul Observatory initiated in 1937 by Peter van de Kamp has been primarily devoted to a detailed astrometric study of the positions of nearby stars from photographs taken with the 24-in. refractor. The accumulation of plates over a long time interval provides the opportunity for finding perturbations of small amplitude leading to the discovery of unseen companions.

Du point de vue de la photometrie, on peut distinguer tres schematiquement trois sortes d'etoiles doubles:

• (1) les couples optiques

• (2) les couples physiques sans orbite connue

• (3) les couples orbitaux.

UBV magnitude differences in visual binaries are presented and their accuracy is discussed. Typical observed image profiles of double stars, including sample profiles of Antares, are shown. This contribution will appear jointly with the earlier one (p. 20) in Lowell Obs. Bull., No. 154. The work has been supported by NSF Grant GP-6983.

Recently, I have carried out, at Lowell Observatory in Flagstaff, very extensive observations of occultations of stars by Moon, in order to get the star diameters, the multiple components and the precise time of occultations by analysis of the distortion of diffraction patterns.

Differences in magnitudes between the components of 874 double stars have been derived from visual estimates on several series of multi-exposure photographic plates. The plates were obtained with long focus refractors primarily for the purpose of determining the relative positions of double stars according to the well-known Hertzsprung method.

Except for binaries with magnitude differences less than half a magnitude, plates were taken with objective gratings limiting the effective magnitude differences between the components to half a magnitude.

Similar to what has been done in variable star work, it was found possible to estimate the magnitude difference to the nearest tenth from this material by visual inspection, using a seven power eyepiece.

The internal mean error of a single estimate of a magnitude is ±0m.064, while the external mean error of a single value in the catalogue based upon an average of three independent determinations is ±0m.054.

Comparisons with other photometric series of this type have been made. In particular the photoelectric series by Eggen (1963,1966) and by Johnson (1953) show close agreements, with no systematic differences.

The results will appear in Publ. U.S. Naval Obs., 2nd Series, 18, Pt. V.

The star was followed photoelectrically in two colors through five consecutive nights in 1968 at Kitt Peak National Observatory. The light of the fainter visual component (a physical companion) was excluded. At primary minimum the system undergoes a total eclipse lasting 25 min. New internally consistent elements have been derived. A subluminous region on the larger star can be located. The previous light curve by Abrami leads to the same geometrical elements but to different photometric elements even when freed from the light of the distant companion.

The paper appeared in Astron. J. 74, 1031 (1969).

J'ai montré ultérieurement les résultats des mesures astrométriques d'étoiles doubles, obtenus au moyen de la caméra électronique. Mais il est certain que Ton doit utiliser, en meme temps, les propriétés intrinseques de ce recepteur pour les mesures photométriques des binaires, complément nécessaire des mesures astrométriques.