THE TRIPLE SYSTEM HD 165590.

High-dispersion spectrograms of the triple system HD 165590 are examined which were obtained during the periastron passage of 1978. The orbital elements are determined by combining the spectroscopic observations with visual observations of the long-period pair. The elements determined include a period of 20.25 yr, an orbital inclination of 82.7 deg, an eccentricity of 0.958, a semimajor axis of 151 billion km, and a longitude of the ascending node of 271.9 deg. A total system mass of 2.51 solar masses and a parallax of 0.024 arcsec are deduced. Reticon observations are discussed which indicate that the short-period binary (0.88-day period) is the visual primary. The spectra of the brighter component of the short-period pair and the visual secondary are shown to be visible in the combined light and to be of approximate types G0 and G5, respectively.