Issue |
A&A
Volume 433, Number 2, April II 2005
|
|
---|---|---|
Page(s) | 629 - 634 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20042291 | |
Published online | 22 March 2005 |
BS Indi: An enigmatic object in the Tucana association*
1
Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany e-mail: guenther@tls-tautenburg.de
2
INAF-Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
3
Università di Salerno, via S. Allende, 84081 Baronissi (SA), Italy
4
MPI für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
Received:
1
November
2004
Accepted:
30
November
2004
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 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.
Key words: stars: individual: BS Ind / binaries: eclipsing / binaries: spectroscopic / stars: formation / stars: evolution
© ESO, 2005
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