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\IBVShead{5175}{15 September 2001}

\IBVStitletl{A 100 Year Period Study of V523 Cassiopeiae:}{ A Triple Star System?}

\IBVSauth{Samec, Ronald G.$^{1}$; Banks, Daniel F.$^1$; Hernandez, Rey$^1$; Faulkner, Danny R.$^{2,4}$;\\ \indent Williams, David B.$^{3}$}

\IBVSinst{Astronomy program, Dept.\ of Physics, Bob Jones University,
Greenville, SC 29614 USA,\\ \indent email: rsamec@bju.edu}

\IBVSinst{The University of South Carolina -- Lancaster, Box 899,
Lancaster, SC 29721 USA, email: faulkner@sc.edu}

\IBVSinst{P.O. Box 58, Whitestown, IN 46075, USA,
email: DBwilyumz@aol.com}

\IBVSinst{Visiting astronomer, Lowell Observatory, Flagstaff, Arizona}

\SIMBADobj{V523 Cas}

\begintext

V523 Cassiopeiae [WR16, CSV 5867, GSC 3257-167] has figured prominently
in studies of very short period K-type non-degenerate eclipsing
binaries over the past 15 years or so.  At 336.5 minutes, its period is
one of the shortest among late type, W UMa contact binaries.  V523 Cas
is also noted for variations in its light curve and for large period
changes. One of the authors (DBW) has acquired 50 times of low light
found from a search of the archival photographic Harvard/SAO plate
stacks. The timings cover the interval from 1901 to 1942 and greatly
extend the baseline over which the period behavior of V523 Cas may be
studied. In addition, seven mean epochs of minimum light were
determined from observations made during three primary and four
secondary eclipses  from 1999 observations at Lowell Observatory
carried out by DRF\@. These times of minimum light are announced in
Table 1 (available electronically through IBVS Web-site as file
5175-t1.txt) with standard errors in parentheses. Also listed is the
starting epoch of our light elements presented below.  These were
combined with the over 400 timings of minimum light available in the
literature (see Table). These span the interval from 1963 to 2001,
yielding a hundred year period history (with a 21 year gap) spanning
nearly 185,000 orbits.  This is probably the longest period study ever
undertaken for a W UMa binary. The amazing results are reported here.

\IBVSedata{5175-t1.txt}

A least-squares linear fit to all available timings resulted in the
following linear light elements:
\begin{equation}
{\rm J.D.~Hel.~Min~I} = 2446708\fday7706(27) + 0.23368973(8)\times E,
\end{equation}
where the probable errors are in parentheses.  The $O-C$ residuals for
Equation (1) are plotted in Figure 1.  The $(O-C)_1$ residuals in Table~1
calculated with these light elements. Mathematically, the data strongly
suggest the sum of a sinusoidal variation and a continuous period
increase.  We fitted the data to just such an equation.  This equation
gives a final ephemeris of:
\begin{equation}
\begin{array}{c}
{\rm J.D.~Hel.~Min~I} = 2446708\fday800(9) + 0.23369099 (18) \times E + {}\\
{} + 1.02(9)\times 10^{-11}\times E^2 + 0.036(5)\times \sin[4.0(0.3)\times 10^{-5} \times E - 1.0(0.1)]. \\
\end{array}
\end{equation}

\IBVSfig{10cm}{5175-f1.ps}{$O-C$ residuals calculated from Equation (1)
for V523 Cas overlain with the sum of a sinusoid quadratic ephemeris.
The sinusoid and quadratic curves also are shown separately}

The fit is plotted with the data in Figure 1, and the $(O-C)_2$
residuals for Equation (2) are given in Table 1. The correlation
coefficient for this excellent fit, $R = 0.97$ (a perfect curve fit
would yield $R^2=1$). The quadratic term, $1\fday02\times10^{-11}\times
E^2$, may be due to mass accretion onto the primary component or some
as yet unexplained physical process causing the binary components to
continuously separate.  Such a continuous period increase or decrease
is not unusual for short period contact binaries.  However, the
sinusoidal behavior with an amplitude of 0.036(5) d (light time:  6.22
AU) is seen only in systems that have a third body present in the
system. Assuming that this is the case, and that the inclination from
our orbital solution for the close pair is the same as the larger
orbit, from Kepler's third law and Equation (2) we obtain a mass for
the third star of 0.37 solar masses.  This is similar to the masses of
the stars that comprise the contact binary. Milone, Hrivnak, and Fisher
(1985) point source model gives a total mass of $\sim0.88$ solar
masses, our simultaneous (using our 1999 light curves) Roche-lobe model
yields  0.96.  The period of the larger system is 101(8) years. If
there is a third member of this system as we suggest here, then from
Figure 1 we see the companion should be near greatest separation now.
The size of the orbit and the distance of the system result in a
maximum angular separation of about 0\farcs3. The expected $V$
magnitude of the companion should be about 15.0.  With adaptive optics
on a large telescope with good seeing it should be possible to resolve
the companion, if it exists.

\bigskip

This research was partially supported by a grant from NASA administered
by the American Astronomical Society.

\clearpage

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