The triple system HD 165590.

High-dispersion spectroscopic observations of the triple system HD 165590 (O2341) were made during the periastron passage of 1978 at the Dominion Astrophysical and the McDonald Observatories. These observations have been combined with the visual observations of the long-period pair in order to determine the orbital elements. They are: P = 20?25, T = 1978.43, a>B = 3?0, U = 271?9, i = 82?7, e = 0.958, a = 1.51 X 109 km, KA = 17.95 km s"' KB = 33.38 km s"' Vo = 22.8 km s"1. The total mass of the system is 2.51 s))l®. A parallax of 0"024 has been deduced. Reticon observations lead us to identify the short-period binary (P = 0?88) as the visual primary, and from this it follows that the ascending node of the orbit (as conventionally defined) is the one at 272°. The spectra of two stars (the brighter component of the short-period pair and the visual secondary) are visible in the combined light and are of approximate types GO and G5, respectively. The mass inferred for the invisible component is consistent with a spectral type of Ml. All three components probably lie on or near the main sequence.