The GALAH survey: unresolved triple Sun-like stars discovered by the
  Gaia mission
  The 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
over-luminous 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 %. 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.
