Nu Gem: A Hierarchical Triple System With An Outer Be Star

Time series of spectroscopic, speckle-interferometric, and optical long-baseline-interferometric observations confirm that nu Gem is a hierarchical triple system. It consists of an inner binary composed of two B-type stars and an outer classical Be star. Several photospheric spectral lines of the inner components were disentangled, revealing two stars with very different rotational broadening (similar to 260 and similar to 140 km s(-1), respectively), while the photospheric lines of the Be star remain undetected. From the combined spectroscopic and astrometric orbital solution it is not possible to unambiguously cross identify the inner astrometric components with the spectroscopic components. In the preferred solution based on modeling of the disentangled line profiles, the inner binary is composed of two stars with nearly identical masses of 3.3 M (circle dot) and the more rapidly rotating star is the fainter one. These two stars are in a marginally elliptical orbit (e = 0.06) about each other with a period of 53.8 days. The third star also has a mass of 3.3 M (circle dot) and follows a more eccentric (e = 0.24) orbit with a period of 19.1 yr. The two orbits are codirectional, and at inclinations of 79 degrees and 76 degrees of the inner and the outer orbit, respectively, about coplanar. No astrometric or spectroscopic evidence could be found that the Be star itself is double. The system appears dynamically stable and not subject to eccentric Lidov-Kozai oscillations. After disentangling, the spectra of the components of the inner binary do not exhibit peculiarities that would be indicative of past interactions. Motivations for a wide range of follow-up studies are suggested.