1 Persei, a low amplitude eclipsing binary, has a period of 25.939 days and an elliptical orbit.

The visual observations of the GEOS, and in particular those made in 1978, have led to a confirmation of the eclipsing binary character of 1 Per and to a determination of its period. These observations have also led to a satisfactory interpretation of the measurements previously published by Kurtz and by the GENEVA observers. 1 Per is therefore an EA-type eclipsing binary with a period of 25.939 days. The orbit is elliptical with an eccentricity of 0.6 and a semi-major axis of 82 R_sun. The inclination of the orbital plane is 1.6°. Secondary minima occur around phase 0.42 for the observational period from 1972 to 1975. An apsidal motion with a period of about 1000 years is probable. Eclipses last respectively 7 hours (primary or "short" minima) and 23 hours approximately (secondary or "long" minima). Both minima have a nearly similar amplitude of 0.22 and 0.21 magnitude (V). The short minima occur shortly before periastron when there is a quasi-total occultation of the companion (with a possible spectrum B5 V) by the principal component (spectrum B1.5 V). The long minima occur before apastron when the principal component is partly eclipsed (22% of the disk surface) by the companion. With a radius about 70 to 75% of that of the principal, the companion has a luminosity which is 4 to 5 times fainter. These values show that the mass of the companion star should be about 2/3 that of the principal. However, this result is not consistent with the radial velocities found in the literature, nor with the fact that 1 Per is not known as a spectroscopic binary. As a consequence, the companion has probably an unusually low mass, though it seems difficult to admit a mass ratio of less than 0.3. As a matter of fact, the interpretation of radial velocity measurements by Beardsley and by Blaauw and van Albada would rather suggest a mass ratio of the order of 0.1 or 0.2. However, the rapid rotation of 1 Per on itself and the presence on its spectrum of lines from the companion (not resolved as yet) should make radial velocity measurements delicate and imprecise. As a matter of fact, the measurements we have used seem to be rather "noisy". New measurements giving a better precision, made at a favorable moment determined with our ephemeris, should lead to a definitive conclusion.