Cotar, K.Zwitter, T.Traven, GregorKos, J.Asplund, MartinBland-Hawthorn, JossBuder, SvenD'Orazi, ValentinaDe Silva, Gayandhi M.Lin, JaneMartell, SarahSharma, SanjibSimpson, Jeffrey D.Nordlander, Thomas2021-05-102021-05-100035-8711http://hdl.handle.net/1885/232558The latest Gaia data release enables us to accurately identify stars that are more luminous than would be expected on the basis of their spectral type and distance. During an investigation of the 329 best solar twin candidates uncovered among the spectra acquired by the GALAH survey, we identified 64 such overluminous stars. In order to investigate their exact composition, we developed a data-driven methodology that can generate a synthetic photometric signature and spectrum of a single star. By combining multiple such synthetic stars into an unresolved binary or triple system and comparing the results to the actual photometric and spectroscopic observations, we uncovered 6 definitive triple stellar system candidates and an additional 14 potential candidates whose combined spectrum mimics the solar spectrum. Considering the volume correction factor for a magnitude-limited survey, the fraction of probable unresolved triple stars with long orbital periods is ∼2 per cent. Possible orbital configurations of the candidates were investigated using the selection and observational limits. To validate the discovered multiplicity fraction, the same procedure was used to evaluate the multiplicity fraction of other stellar types.KC, TZ, and JK acknowledge financial support of the Slovenian Research Agency (research core funding No. P1-0188 and project N1-0040). This research was partly supported by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. YST is supported by the NASA Hubble Fellowship grant HSTHF2-51425.001 awarded by the Space Telescope Science Institute.application/pdfen-AU© 2019 The Author(s)methods: data analysisbinaries: generalstars: solar-typeGalaxy: stellar content2019-05-2110.1093/mnras/stz13972020-12-27