  BS Ind is a young K0V star in the Tucana association. Photometric
observations with the Hipparcos satellite show an eclipse-like light-curve with
primary and secondary eclipse. The eclipsing binary has a period of 0.435338
days and a circular orbit. Our spectroscopic observations however show that the
K0V primary is a single-line spectroscopic binary with a period of 3.3 years.
The minimum mass of the invisible component is about 0.9 Mo which means that
the mass of the companion is about the same as that of the primary. The first
inspection of our FEROS spectra, as well as a CES spectrum shows no obvious
companion. However, when the FEROS spectra are cross-correlated with an M-star,
a secondary becomes visible as a broad peak in the cross-correlation function.
The width and the position of this broad peak is variable on a short
time-scale. When phased to a period of 0.435338 days, the radial velocity
variations of the broad peak show the characteristic sine-wave of a
spectroscopic binary in a circular orbit. The best interpretation of this data
is that the broad peak in the cross-correlation function is caused by an
eclipsing binary consisting of two late-K, or early-M stars with an orbital
period of 0.435338 days. This is the eclipsing system. These two stars then
orbit the K0V-primary with a period of 3.3 years. The assumption that BS Ind is
a triple system consisting of a K0V star and two late-K, or early-M stars also
explains the unusual brightness of the object and the near infrared excess.
Thus, BS Ind is unique, as it contains by far the shortest-period young binary
star, and these stars are eclipsing.
