Issue |
Astron. Astrophys. Suppl. Ser.
Volume 145, Number 1, July 2000
|
|
---|---|---|
Page(s) | 161 - 183 | |
DOI | https://doi.org/10.1051/aas:2000346 | |
Published online | 15 July 2000 |
Re-processing the Hipparcos Transit Data and Intermediate Astrometric Data of spectroscopic binaries*
I. Ba, CH and Tc-poor S stars
Institut d'Astronomie et d'Astrophysique, Université Libre de Bruxelles, CP. 226, Boulevard du Triomphe, B-1050 Bruxelles, Belgium
Send offprint request to: pourbaix@astro.ulb.ac.be
Received:
4
November
1999
Accepted:
4
May
2000
Only 235 entries were processed as astrometric binaries with orbits in the
Hipparcos and Tycho Catalogue (ESA 1997). However, the
Intermediate Astrometric Data (IAD) and Transit Data (TD) made
available by ESA make it possible to re-process the stars that turned
out to be spectroscopic binaries after the completion of the
Catalogue. This paper illustrates how TD and IAD may be used in
conjunction with the orbital parameters of spectroscopic binaries to
derive astrometric parameters. The five astrometric and four orbital
parameters (not already known from the spectroscopic orbit) are
derived by minimizing an objective function () with an
algorithm of global optimization. This code has been applied to 81
systems for which spectroscopic orbits became available recently and
that belong to various families of chemically-peculiar red giants
(namely, dwarf barium stars, strong and mild barium stars, CH stars,
and Tc-poor S stars). Among these 81 systems, 23 yield reliable
astrometric orbits. These 23 systems make it possible to evaluate
on real data the so-called “cosmic error” described by
Wielen et al. (1997), namely the fact that an unrecognized orbital motion
introduces a systematic error on the proper motion. Comparison of the
proper motion from the Hipparcos catalogue with that re-derived in the
present work indicates that the former are indeed far off the present
value for binaries with periods in the range 3 to ~ 8 years.
Hipparcos parallaxes of unrecognized spectroscopic binaries
turn out to be reliable, except for systems with
periods close to 1 year, as expected. Finally, we show that, even when
a complete orbital revolution was observed by Hipparcos, the
inclination is unfortunately seldom precise.
Key words: methods: data analysis / astrometry / binaries: spectroscopic / stars: late-type / stars: fundamental parameters
© European Southern Observatory (ESO), 2000