Zeta Capricorni

Properties

The binary nature of this system was announced in 1980 by Erika Böhm-Vitense based on an ultraviolet excess attributed to a white dwarf companion. It is a single-lined spectroscopic binary system. Based on an incomplete orbital arc, the orbital period for this system is 6.5 years and the eccentricity (ovalness) is 0.28. It was flagged as a suspected eclipsing binary in 1988 due to observed variations in the light curve.

The primary, designated component A, has a stellar classification of G4Ib: Ba2. This notation indicates this is a yellow-hued supergiant star, although the ':' means there is some uncertainty about the class. The temperature and surface gravity of this object suggests it may be a horizontal-branch star. It is considered a prototypical example of a Barium star, as indicated by the 'Ba2' class suffix. The properties of these objects include overabundances of carbon molecules (such as C₂) and s-process elements. Zeta Capricorni has an overabundance of the s-process element praseodymium.

Its companion, component B, is a carbon-oxygen white dwarf with a hydrogen-rich atmosphere and a class of DA2.2. It is about as massive as the Sun, and its temperature is 23,000 K. In the course of its evolution, the progenitor star passed through the thermally pulsing asymptotic giant branch, during which the enlarged atmosphere transferred material to the primary. The abundance of niobium in the primary's atmosphere, a product of the decay of zirconium-93, is at a level that suggests the transfer to the primary took place more than three million years ago.

A magnitude 12.5 visual companion was discovered by T. J. J. See in 1897. As of 1997, it was located at an angular separation of 17.30″ along a position angle of 12°.