A study of the motion of the star Gliese 623 with a low-mass dark companion on the basis of observations at Pulkovo

Abstract

Abstract Photographic observations of the nearby star Gliese 623 (AC 48° 1595/1589) with an optically invisible companion of extremely low stellar mass have been made during the years 1979–1995 by means of 26-inch refractor at Pulkovo. The relative proper motion and relative parallax have been obtained on the basis of 89 plates (580 individual positions). The residuals with a mean error of ±0.011 arcsec have been calculated. The motion of the photocentre evoked by the companion has been estimated by means of these residuals. The following dynamic elements are chosen for the photocentric orbit: P = 3.76 years, e = 0.51, To = 1984.3. The most stable geometrical element is the great semi-axis of the photocentre α which equals 0.052 ± 0.007 arcsec (m.e.). The values of i, Ω and Ω have shown some change for different intervals of observations and are due to systems of reference stars. The lower limit of the mass of the companion is estimated as 0.09 ± 0.03 solar masses. The positions of the main star on the ea...