BS Indi: An enigmatic object in the Tucana association

Details BS Indi: An enigmatic object in the Tucana association BS Indi: An enigmatic object in the Tucana association

Apr 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005a%26a...433..629g&link_type=abstract

Astronomy and Astrophysics, Volume 433, Issue 2, April II 2005, pp.629-634

Astronomy and Astrophysics

Astrophysics

6

Stars: Individual: Bs Ind, Binaries: Eclipsing, Binaries: Spectroscopic, Stars: Formation, Stars: Evolution

Scientific paper

BS Ind (=HD 202947) 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 M_&sun; which means that the mass of the companion is about the same as that of the primary. The first inspection of our FEROS spectra with a resolution of 48 000, as well as a CES spectrum with a resolution of 220 000 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. 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.
Based on observations obtained at the European Southern
Observatory at La Silla, Chile in program
62.I-0418, 63.I-0096, 64.I-0294, 65.I-0012,
67.C-0155, 68.C-0292, 69.C-0207, 70.C-0163,
072.A-9012, 073.C-0355 and 67.C-0194.

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