| Issue |
A&A
Volume 469, Number 1, July I 2007
|
|
|---|---|---|
| Page(s) | 285 - 296 | |
| Section | Stellar structure and evolution | |
| DOI | https://doi.org/10.1051/0004-6361:20066911 | |
| Published online | 24 April 2007 | |
Absolute dimensions of eclipsing binaries *,**
XXV. U Ophiuchi and the evolution and composition of
5 M
stars
1
Departamento de Física, ICEX–UFMG, C.P. 702, BR-30.123-970 Belo Horizonte, MG, Brazil e-mail: lpv@fisica.ufmg.br
2
The Niels Bohr Institute, Astronomy, Juliane Maries Vej 30, 2100 Copenhagen, Denmark e-mail: ja@astro.ku.dk
3
Nordic Optical Telescope Scientific Association, Apartado 474, 38 700 Santa Cruz de La Palma, Spain
4
Instituto de Astrofísica de Andalucía, CSIC, Apartado 3004, 18 080 Granada, Spain e-mail: claret@iaa.es
Received:
11
December
2006
Accepted:
29
March
2007
Context.Precise stellar masses and radii provide unique information on stellar evolution. In a Galactic context, they may also provide information on the evolution of the Solar neighbourhood.
Aims.We aim to determine absolute dimensions for the mid B-type eclipsing binary
U Ophiuchi and compare
the inferred ages and chemical compositions to those
of other binary stars with masses near 5 
.
Methods.We determine
masses, radii, 
, 
, and
luminosities for the stars in
U Oph from new radial velocities and uvby light curves. By
improving the Wilson-Devinney code, we also derive precise
apsidal-motion and light-time orbits of this triple system, using 353 times of
minimum over 120 years. Finally, we compare the data for U Oph and
three similar systems with the predictions of stellar models.
Results.The stars in U Oph have masses of 5.27 ± 0.09 and
4.74 ± 0.07 , radii of
3.48 ± 0.02 
and
3.11 ± 0.03 ; we argue that systematic
errors are negligible.
The apsidal motion period is exceptionally short, 
yr,
while the light-time orbit has 
38.4 yr. The
precise values for DI Her, U Oph,
V760 Sco, and MU Cas, all within
10% of 5 , place them
successively from the ZAMS to the TAMS, at ages of 5-100
106 yr.
Current stellar evolution models fit both stars
in each system very
well if the (otherwise unconstrained)
metal abundance Z is adjusted in each case.
Conclusions.More accurate
data and/or binary systems with larger mass ratios are
needed to actually test stellar models near 5 . The
different Z values found for these young, nearby systems suggest
that disk stars form with a range of metal abundances even today, but
more data are needed to confirm this result.
Key words: stars: binaries: eclipsing / stars: fundamental parameters / stars: evolution / Galaxy: evolution
© ESO, 2007
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