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The study of V 839 Oph shows that it is an A-type W UMa eclipsing system
and that the common envelope of the system has a structure with convective
"continents'' on a radiative envelope. Examination of our solutions for the
period variations and the light curve leads to the following conclusions.
In this paper, we have found that the current period of V 839 Oph increases
in time. On top of this, it seems likely that the period also oscillates
sinusoidally with a period of years. At the moment we cannot
give a unique explanation for these oscillations but we have made several
suggestions. It is clear that only systematic and continuous
photometric and spectroscopic observations help to understand the connection
between light curve and the period variation.
- Our solution for the period variation of V 839 Oph indicates that
the mass transfer rate from the less massive component to the more massive
component is higher than expected for an A-type (Cruddace & Dupree
1984). For this system we find .
- If the sinusoidal variations are due to conservative
mass transfer in the system, the mass should have flown from the primary to
the secondary between 1978-1988, and from the secondary to the primary
between 1988-1998. It seems that such a frequent shift (every yr)
in the direction of mass transfer is not possible dynamically.
- One other possible mechanism for the sinusoidal variations
is a third body in the system. For a hypothetical third body, the period
() and semi-amplitude (0.0065 d) of the sinusoidal
variations in Fig. 4 (click here) lead to a small mass function of f(M3)=0.00376
. We obtain with the assumption of circular
and co-planar orbits of the third body. The semi-major axis a3 of third
body orbit around the center of mass of the triple system is about .
The bolometric absolute magnitude of the third body was found to be
using the mass-luminosity function;
for (Demircan & Kahraman 1991).
The third body, if it exists, should revolve much beyond the outer Lagrangian
points of V 839 Oph, if it were to be stable.
- Another possible mechanism to explain the sinusoidal period
variation of V 839 Oph is a period modulation mechanism described by
(1992) due to magnetically induced deformations in the outer layers of one of
the two components. This mechanism can however not be tested at present,
since not enough data is available about the level of the minima and maxima
of the light curves, to compare with detailed models. Assuming that the
primary component is the active component, we estimate, by using
(1992) formula, that an angular momentum transfer of
is needed to produce the
observed orbital period change in the 19.62 yr cycle that is . The subsurface mean magnetic field of the primary then should be
about 8.21 kG. According to the discussion in photometric solution section,
if the presence of magnetic spots could create a long-term light variation
which is strongly possible but, unfortunately now, we cannot discuss the
possible relation between the long-term light curve variation and their
probable connection with the sinusoidal period variation cause of absence
enough light curves on published.
We should admit that in last few years, however the period modulation
mechanism seems to be the main cause of such periodicities, the insufficient
light curves on literature cannot give permit to reach final conclude in many
of W UMa systems, for example, V 839 Oph (the present work), BX And
et al. 1993), AB And (Demircan et al. 1994b,
Kalimeris et al. 1994), DK
Cyg (Awadalla 1994)
while except well observed systems, for example, SW Lac
(Glownia 1986), VW Cep (Karimie 1983)
and TZ Boo (Awadalla 1989).
We express our thanks to Dr. R.F. Peletier for help with the presentation.
We are greatly indebted to the referees, Drs. A. Gimenez and A. Claret for
valuable suggestions and helpful comments. Thanks are due to Dr. Z.
Müyesseroğlu for helpful running of Wilson-Devinney code. We are
grateful to the amateur astronomer, H.E. Kum, for his careful
observations and participation to the observation program.
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