All times of minima of V 839 Oph available in the literature have been
compiled, which altogether contain 71 times of minimum light (24 visual,
3 photographic and 44 photoelectric), cover about 45000 orbital
revolutions, and thus provides important new information about the change of
the orbital period of the system. There are however 2 big gaps in the data.
One, following the discovery by Rigollet (1947), contain cycles,
while the other, between the first group of photometric times of minima and
the second visual time of minima, contains cycles. The first
minimum is visual, as are many around *E*=-20000. However, one can see that the
visual estimates in general show a large amount of scatter. Rigollet's
minimum is of good quality, because his light curve contains 131 visual
estimates.

The diagram which is calculated using the present work's linear ephemeris are shown in Fig. 2 (click here) and are listed as in Table 5 (click here) (available in electronic form). This form of the diagram indicates clearly that the orbital period of V 839 Oph is increasing. Both primary and secondary times of minima follow the same trend on the diagram.

**Figure 2:** The () diagram of V 839 Oph is shown is a quadratic fit
through the data points. Photometric data (asteriscs),
photographic data (squares) and visual data (diamonds) are
shown

We fitted a quadratic function to the distribution of
variations using all photometric and photographic times of minima together
with the first visual time (see Fig. 2 (click here)). The following quadratic ephemeris
was obtained:

where the coefficient of the square term represent the rate of change
of the period (), which is acceptable. In
fact, such a representation of the data is statistically much better
than the alternative (linear) representation.
The residuals from the quadratic ephemeris are also listed in
Table 5 (click here) and displayed Fig. 3 (click here)a. We found for the goodness of fit
==0.000033.
If the period increase is purely due to the conservative mass
transfer from the less massive to the more massive component (from
to (Al-Naimy et al. 1989))
then with the equation ,
such a transfer rate would be about
for the period variation.
After fitting the parabolic form, we also applied to the residuals a
sinusoidal fit of the form

**Figure 3:** The calculated residuals from **a)** the quadratic ephemeris,
**b)** the best sinusoidal fit

to all photographic and photoelectric times of minimum light include
first Rigollet's visual time. Here , and
are the
half-amplitude (in days), the period (in days), and a minimum time
(in units of *E*) of the proposed sine curve of the diagram,
respectively. We found that the data are best represented
by the following
sinusoidal ephemeris:

The best-fitting parabolic and sinusoidal curves are displayed,
superimposed on the observational data, in Fig. 4 (click here). The residuals
from the best fit, which are listed in Table 5 (click here) and displayed in Fig. 3 (click here)b
and the goodness of fit of the representation,
is
much better than that of the previous quadratic one. The period of the
cyclic variation is 19.62 yrs.

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