Apsidal motion and the third body in the system RU Monocerotis

• Published in: Monthly notices of the Royal Astronomical Society Vol. 216; no. 4; pp. 909 - 922
• Main Authors: Khaliullina, A. I., Khaliullin, Kh. F., Martynov, D. Ya
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford University Press 01.10.1985; Blackwell Science
• Subjects: Astronomy; Binary and multiple stars; Earth, ocean, space; Exact sciences and technology; Multiple stars; Stars; Apsidal motion; Triple star
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/216.4.909

A third body with a mass ${M}_{3}\simeq 2.2 {M}_{\odot}$ has been discovered in the system RU Man from the period variations observed over 80 years. Parameters of the long-period orbit have been determined: ${P}_{3}=67.6\,\text{yr},\,{a}_{3}\,\text{sin}\,{i}_{3}=8.36$ AU, ${e}_{3}=0.4,\,{\omega}_{3}={230}^{\circ}$. The limits on the third light have been obtained from analysis of the photoelectric light curve: $L_{3}^{V}\lt0.05$. This means that the third body cannot be a single star on the main sequence. A new value of the apsidal motion velocity has been obtained: $\dot{\omega}=(1^\circ.034\pm0^\circ .042)\,\text{yr}^{-1}$, corresponding to an apsidal period U=(348±15) yr. The apsidal parameter value, ${k}_{2,\,1}\simeq {k}_{2,\,2}=0.0061$, determined from observations is in good agreement with the theoretical values for models of main-sequence stars.