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\IBVShead{4597}{3 June 1998}

\IBVStitle{TIMES OF MINIMA OF ECLIPSING BINARIES}


\IBVSauth{CLAUD H. SANDBERG LACY$^1$, JAMES L. CLEM$^1$, MAMNUN ZAKIROV$^2$, G.C. ARZUMANYANTS, N.R. BAIRAMOV$^2$, A.S. HOJAEV$^2$}

\IBVSinst{Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA}
\IBVSinst{High Altitude Maidanak Observatory, Astronomical Institute, Tashkent 700052, Uzbekistan}

\begintext


	We report times of minima of eclipsing binaries derived from 
photometric observations made at the High Altitude Maidanak Observatory in 
Uzbekistan in Johnson B,V filters, and at the University of Arkansas 
(unfiltered CCD observations; all but one of the Arkansas minima were
observed by JLC). 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 Maidanak 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 
the 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.

\vskip 2mm
\centerline{Table 1}
\vskip 1mm
\begin{center}
\begin{tabular}{lccl}
\hline
	Star &JD of Min	$-$2400000&Type&Observatory\\
\hline
\\		       
	KP Aql	&  50670.6586 $\pm$ 0.0008	&  1&	Arkansas\\
 & & & \\
	WW Cam	&  50319.3520 $\pm$ 0.0005&	  2	&Maidanak\\
		&  50667.3343 $\pm$ 0.0004&	  2	&Maidanak\\
		&  50675.3063 $\pm$ 0.0005&	  1	&Maidanak\\
		&  50843.6054 $\pm$ 0.0002&	  1	&Arkansas\\
		&  50852.7028 $\pm$ 0.0003&	  1	&Arkansas\\
		&  50868.6209 $\pm$ 0.0004&	  1	&Arkansas\\
 & & & \\
	AY Cam	&  50847.7598 $\pm$ 0.0004&	  1&	Arkansas\\
 & & & \\
	IT Cas	&  50848.6032 $\pm$ 0.0009&	  1&	Arkansas\\
 & & & \\
	PV Cas	&  50321.4771 $\pm$ 0.0006&	  2&	Maidanak\\
 & & & \\
	V459 Cas&  50307.3162 $\pm$ 0.0005&	  1&	Maidanak\\
 & & & \\
	EK Cep&	  50311.3135 $\pm$ 0.0004&	  1&	Maidanak\\
\hline
\end{tabular}
\end{center}

\vskip 2mm
\centerline{Table 1 (cont.)}
\vskip 1mm
\begin{center}
\begin{tabular}{lccl}
\hline
	Star &JD of Min	$-$2400000&Type&Observatory\\
\hline
\\		
        RT CrB&	  50640.3389 $\pm$ 0.0010&	  1&	Maidanak\\
 & & & \\
	V442 Cyg&  50725.7468 $\pm$ 0.0003&	  2&	Arkansas\\
 & & & \\
	V541 Cyg&  49935.3911 $\pm$ 0.0006&	  2&	Maidanak\\
 & & & \\
	V909 Cyg & 50284.3338 $\pm$ 0.0004&	  2	&Maidanak\\
		 & 50305.3752 $\pm$ 0.0003&	  1	&Maidanak\\
		 & 50312.3868 $\pm$ 0.0010&	  2	&Maidanak\\
		 & 50319.3520 $\pm$ 0.0005&	  2	&Maidanak\\
		 & 50622.3782 $\pm$ 0.0030&	  1	&Maidanak\\
		 & 50629.3962 $\pm$ 0.0020&	  2	&Maidanak\\
		 & 50653.2405 $\pm$ 0.0010&	  1	&Maidanak\\
		 & 50660.2535 $\pm$ 0.0010&	  2	&Maidanak\\
		 & 50689.7076 $\pm$ 0.0004&	  1	&Arkansas\\
		 & 50682.6993 $\pm$ 0.0007&	  2	&Arkansas\\
 & & & \\
	V364 Lac & 49947.4106 $\pm$ 0.0010	 & 1	&Maidanak\\
		 & 50686.3545 $\pm$ 0.0009	 & 2	&Maidanak\\
 & & & \\
	RU Mon	 &50837.6714 $\pm$ 0.0004	&  1&	Arkansas\\
\hline
\end{tabular}
\end{center}
\vskip 2mm

	For some of the binaries, JLC has collected from the literature
all published dates of minima in order to improve the eclipse ephemerides.
Based on a preliminary analysis of all data, visual dates of minima were
assigned a standard error of 0.014 days, photographic dates were assigned
a standard error of 0.018 days, relatively old photoelectric minima were
assigned a standard error of 0.0037 days, and recent photoelectric minima
were assigned a standard error of 0.0020 days unless the standard error
was explicitly stated in the publication.  A weighted least squares fit
to the dates of minima resulted in the improved ephemerides listed in Table 2.

\vskip 2mm
\centerline{Table 2}
\vskip 1mm
\begin{center}
\begin{tabular}{lrl}
\hline
	Star	&           Period (days)	&Zero Epoch (HJD)$-$ 2400000\\
\hline
\\
	KP Aql	& Min I	3.3674753 $\pm$ 0.0000005	&50670.6586 $\pm$ 0.0003\\
		 &Min II	3.3674748 $\pm$ 0.0000008	&49931.4981 $\pm$ 0.0017\\

	WW Cam	& Min I	2.2743614 $\pm$ 0.0000006	&50843.6050 $\pm$ 0.0002\\
		& Min II	2.2743634 $\pm$ 0.0000023	&41781.3914 $\pm$ 0.0056\\

	AY Cam	& Min I	2.7349681 $\pm$ 0.0000004	&50847.7597 $\pm$ 0.0003\\
		 &Min II	2.7349627 $\pm$ 0.0000014	&49555.4675 $\pm$ 0.0042\\

	IT Cas	& Min I	3.8966431 $\pm$ 0.0000008	&50848.6186 $\pm$ 0.0006\\
		& Min II	3.8966489 $\pm$ 0.0000009	&49962.3378 $\pm$ 0.0008\\

	V442 Cyg &Min I	2.3859454 $\pm$ 0.0000011	&44919.5609 $\pm$ 0.0037\\
		& Min II	2.3859378 $\pm$ 0.0000009	&50725.7472 $\pm$ 0.0003\\

	V909 Cyg& Min I	2.8053850 $\pm$ 0.0000009	&50689.7076 $\pm$ 0.0004\\
		 &Min II 2.8053881 $\pm$ 0.0000011	&50682.6994 $\pm$ 0.0007\\
\hline
\end{tabular}
\end{center}
\vskip 5mm

	
	Differences between the periods for Min I and Min II are expected
for the eccentric eclipsing binary IT Cas due to apsidal motion (Lacy et
al. 1997). The period of RU Mon, however, is found to be quite variable,
suddenly increasing or decreasing in value (the average period is 3.5846
days, with sudden variations at the level of 0.0001 days), and cannot be 
well represented by a single linear ephemeris.  RU Mon is discussed by
Martynov \& Khaliullin (1986). This erratic behavior cannot be due to
simple apsidal motion mechanisms, and is likely due to some kind of mass
loss or transfer, or some unknown mechanism.
	We would like to acknowledge financial support of our work by the 
American Astronomical Society through the Edith J. Woodward Award and from the 
Margaret Cullinan Wray Charitable Lead Annuity Trust.

\references

Kwee, K.K., and van Woerden, H., 1956, {\it B.A.N.}, {\bf 12}, 327

Lacy, C.H.S., Torres, G., Latham, D.W., Zakirov, M.W., \& Arzumanyants,
  G.C. 1997, {\it AJ}, {\bf 114}, 1206

Martynov, D. Ya., \& Khaliullin, Kh. F., 1986, {\it Astron. Zh.}, {\bf 63}, 288


	
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