Issue |
Astron. Astrophys. Suppl. Ser.
Volume 134, Number 1, January I 1999
|
|
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Page(s) | 1 - 19 | |
DOI | https://doi.org/10.1051/aas:1999122 | |
Published online | 15 January 1999 |
Variations of the orbital periods in semi-detached binary stars with radiative outer layers
Astronomical Institute, Academy of Sciences, 251 65 Ondřejov, Czech Republic
Send offprint request to: V. Šimon
Received:
29
January
1998
Accepted:
23
June
1998
A detailed analysis of the period changes of sixteen semi-detached binaries
which contain only stars with radiative outer layers (ET-systems) has been
performed and their respective O–C diagrams are brought and discussed. It
was found that the course of the period variations is monotonic and in some
systems the period is even constant. This detailed analysis of extensive sets
of timings covering several decades brings a strong support to an earlier
finding of Hall (1989) and develops it further. We show that all systems with
the orbital periods shorter than nine days display constant period or its
increase, with the exception of an uncertain case of V 337 Aql. The course of
the period variations in TT Aur appears more complex but the cyclic term can
be plausibly explained by the third body.
A search for general relations between the parameters of the systems and the
period changes was undertaken. The mass ratio q appears to play a role in
the period variations. Clear changes in systems with orbital periods shorter
than 9 days were detected only for while constant periods are common
in systems with
in this period range. The sense of the secular
changes in most systems is in accordance with the dominant conservative mass
transfer in evolved binary and corresponds to the slow phase. The role of the
evolutionary scenarios (case A versus B) and the influence of changes of the
rotational angular momenta of the components are discussed.
Key words: stars: activity / binaries: eclipsing / binaries: close / circumstellar matter / stars: early- type / stars: evolution
© European Southern Observatory (ESO), 1999