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\IBVShead{4737}{23 July 1999}

\IBVStitle{Times of Minima of Eclipsing Binaries}

\IBVSauth{CLAUD H. SANDBERG LACY$^1$, KYLE MARCRUM$^1$, CAFER IBANOGLU$^2$}

\IBVSinst{Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA}

\IBVSinst{Astronomy \& Space Sciences Department, Ege University, Izmir, Turkey}

\begintext

We report times of minima of eclipsing binaries derived from photometric observations made by CI at the Ege University Observatory in Turkey in Johnson $B,V$ filters, and at the University of Arkansas (unfiltered CCD observations made by KM).  Heliocentric times of minima were estimated for each filter by using the method of Kwee and van Woerden (1956) as adapted to a Macintosh computer.  The adopted time of minimum was then the average over both filters for Ege data.  In all cases the times of minima in different filters were concordant.  Uncertainties in the times of minima were estimated from the values of standard error computed by the method and from differences in times derived from the various filters used.  In Table~1, primary eclipses are designated as type 1 eclipses, and secondary eclipses as type 2.

\begin{table}[h]
\begin{center}
{\normalsize Table 1}
\vskip2mm
\begin{tabular}{llclc}
\hline
Star & ${\rm JD~of~Min - 2400000}$ & Type & Observatory & Notes \\
\hline
WW Cam   & $51134.7232\pm0.0004$ & 1 & Arkansas \\
V459 Cas & $51144.6845\pm0.0005$ & 1 & Arkansas \\
WW Cep   & $51141.6161\pm0.0005$ & 2 & Arkansas & 1 \\
RW Lac   & $51076.6925\pm0.0005$ & 2 & Arkansas & 2 \\
V530 Ori & $51199.2593\pm0.0005$ & 1 & Ege      & 3 \\
BP Vul   & $51063.6717\pm0.0003$ & 1 & Arkansas \\
         & $51128.645 \pm0.005 $ & 2 & Arkansas \\
         & $51129.646 \pm0.001 $ & 1 & Arkansas \\
\hline
\end{tabular}
\end{center}
\end{table}

\noindent{\bf Notes:}

1. The period listed in the GCVS is almost exactly 1/3 of the true period found by Torres (1998)  from spectroscopic observations as $4.600843 \pm 0.000054$ days. From dates of minima found in the eclipsing binary minima database at the web site \\
\centerline{\tt http://www.oa.uj.edu.pl/ktt/index.html} 
we find 
$$
{\rm Min~I} = 4.600841 \times n + 2449218.4631.
$$
From the zero epoch in the GCVS and our observation, assuming a circular orbit (consistent with published dates of minima), we find a period of 4.600849 days, in agreement with the spectroscopic value. The origin of the error in the GCVS period is unknown.

2. Recent spectroscopic observations by Torres (1998) indicate that secondary eclipse now occurs at a phase of $0.491 \pm 0.001$ due to an eccentric orbit. Our observed time of secondary eclipse is in agreement with this prediction. The eccentricity is approximately 0.014 based on the spectroscopic data. 

3. Our observation may be combined with the observations of Lacy \& Fox (1994) to yield an orbital period of $6.110777 \pm 0.000002$ days (assuming a constant period). This appears to be consistent with the period listed in the GCVS, but is more accurate.

\IBVSfig{10cm}{4737-f1.ps}{A typical observation of a primary eclipse}

\references

Kwee, K.K., and van Woerden, H. 1956, BAN, 12, 327

Lacy, C.H.S., \& Fox, G.W. 1994, IBVS, No.\,4009

Torres, G. 1998, private communication

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