Sarah Lee Lippincott

Astrometric search for unseen stellar and sub-stellar companions to nearby stars and the possibility of their detection

Unseen companions to nearby stars are found astrometrically through perturbations in the proper motion from photographs taken with long-focus telescopes. The number of known unseen astrometric companions to nearby stars with photocentric orbits has grown by thirty percent in the last few years. Individual cases are discussed and optimum epochs given for resolution of the components. Orbital analysis of the photocentric positions on the photographic plates provides all information for accurate mass determination of the components except for Δm and angular separation, ϱ, of the two components which must come from another technique. There are potentially thirty low luminosity stars including some likely sub-stellar objects whose masses could be instantly found with the observations of these additional two parameters.A list of the stars known within five parsecs as of 1978 July is given and the status of unseen companions to these stars is discussed on the basis of long interval astrometric coverage.

AN UNSEEN COMPANION TO 36 URSAE MAJORIS A FROM ANALYSIS OF PLATES TAKEN WITH THE SPROUL 61-CM REFRACTOR.

Astrometric analysis of plates taken on 36 UMa A with the Sproul 61-cm refractor indicate variable proper motion which can be explained by Kepler motion for a photocentric orbit with a period of 18 years. An unseen red-dwarf companion is indicated with a mass of about 0.07 solar mass. This additional companion makes the 36 UMa system at least quadruple. The Sproul relative parallax of the system is + 0.0738 arscec + or - 0.0028 arcsec as determined by the A component.

PARALLAXES, MASS RATIOS, AND MASSES FROM THREE VISUAL BINARIES.

Astrometric studies of ADS 4299, ADS 8048, and ADS 9352 from plates taken with the Sproul 61-cm refractor yield parallaxes, proper motions, mass ratios, and masses. The masses and luminosities are appropriate, within the probable errors for main-sequence stars. The latter two systems have distant proper-motion companions.