SPECTROSCOPIC ORBIT OF THE TRIPLE STAR 55-URSAE-MAJORIS

The first investigation of the known triple system 55 UMa (2.55d binar y in a similar to 1870-d orbit with the third star) based on electroni c spectra led to several new findings about the system: (1) Discovery of spectral lines of the tertiary and an unambiguous detection of the lines of the secondary. Spectra of both primary and tertiary are of th e same strength and correspond to spectral class AOV. The secondary sp ectrum is about twice fainter in the visual region and belongs probabl y also to spectral class A. (2) First self-consistent orbital solution describing close and wide orbit and the detection of apsidal motion f or the close pair. The orbital period of the close pair was improved t o (2.5538380d +/- 0.0000046d) and basic physical elements for all thre e stars and the system were estimated. The orbital solution also gives the period of apsidal motion of the close pair of (450 +/- 60) yr and leads to a good agreement with the published speckle-interferometric orbit for the distant companion if the longitude of periastron passage is increased by 180 degrees.