Orbits of spectroscopic binary systems have been studied for more than a century. Over
three thousand orbits of spectroscopic binary systems have been derived. These orbits
are based on the radial velocities measured from the spectra recorded by a photographic
plate to a high precision spectrum observed from a modern spectrograph. In many cases,
the shape of the orbit was assumed to be circular, of hence the eccentricity is zero. This
assumption is based on the fact that a small eccentricity (e < 0.1) measured from the
observed data might be a result from the error of observations or from the intrinsic
variation of a spectroscopic binary system.
Sixteen southern spectroscopic binary systems, including twelve single-lined binaries
and four double-lined binaries, were selected to study in this research program. These
systems were assumed to have circular orbits or have very nearly circular orbits (e <
0.1) from their previous published solutions. The HERCULES spectrograph was used
in conjunction with the 1-m McLellan telescope at Mt John University Observatory
to collect the spectra of these systems. The observations, taken from October 2004
to August 2007, comprised about 2000 high-resolution spectra of spectroscopic binary
systems and standard radial-velocity stars. Radial velocities of spectroscopic binary
systems were measured from these spectra and orbital solutions of the systems were
derived from these radial velocities.
It was found that from HERCULES data, we are able to achieve high-precision orbital
solutions of all the systems studied. The best-fit solutions can be improved as much as
70 times from the literature’s orbital solutions. It has been found that the precision of
a system depends on the rotational velocities of the components as well as the level of
their chromospheric activity.
We are able to confirm the eccentricity in the orbit of only one of the selected spectroscopic
binary systems, HD194215. Its eccentricity is 0.123 29 ± 0.000 78. The small
eccentricities of other systems are not confirmed.
There are four systems; HD22905, HD38099, HD85622 and HD197649, that have
circular orbital solutions from the large errors in their measured eccentricities. Two
systems, HD77258 and HD124425, have too small eccentricities, e = 0.000 85±0.000 19
and 0.002 60 ± 0.000 99 to be acceptable.
An intrinsic variation is a presumed cause of the spurious eccentricities derived from
the data of the other eight systems. Photometric data from Mt John University Observatory
service photometry program, as well as the photometric data from the Hipparcos
satellite and information of these systems from the literature, using various methods and
instruments, give a wider view on the systems’ behaviour.
It is possible that the spurious eccentricities derived for these systems result from
the eclipsing behaviour of a system (HD50337), or from the nature of the components,
such as, the distortion of their shape (HD352 and HD136905), their chromospheric
activity (HD9053, HD3405, HD77137, HD101379 and HD155555), or stellar pulsation
(HD30021).
Models of the active chromosphere system, HD101379, have been simulated. An
analysis of synthetic radial velocity data shows that spots on the star’s photosphere can
cause a spurious eccentricity. The values of the spurious eccentricity and the longitude
of periastron are dependent on the spot size, the spot temperature, and the position of
the spots.
| Identifer | oai:union.ndltd.org:canterbury.ac.nz/oai:ir.canterbury.ac.nz:10092/1590 |
| Date | January 2008 |
| Creators | Komonjinda, Siramas |
| Publisher | University of Canterbury. Department of Physics and Astronomy |
| Source Sets | University of Canterbury |
| Language | English |
| Detected Language | English |
| Type | Electronic thesis or dissertation, Text |
| Rights | Copyright Siramas Komonjinda, http://library.canterbury.ac.nz/thesis/etheses_copyright.shtml |
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