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\IBVShead{4167}{8 March 1995}

\title{PRECISION B,V LIGHT CURVES OF EK COMAE BERENICES}
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\begintext

        EK Comae Berenices was discovered by Kinman et al. (1966) in a study 
of fields near the north galactic pole.  He identified it as a W UMa variable.
The paper includes accurate positions,  a finder chart, and a list of 
photographic magnitudes giving a range of 12.7 to 13.4 mag.  This binary 
was brought to our attention by AAVSO observer Borovicka (1990),  
who conducted a thorough visual investigation determining 
the preliminary light elements to be:
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\hspace*{25mm}JD Hel Min.\,I = 2447609.405 + 0\fd 2666874$\times$E. \hfill  (1)
\hspace*{7.3cm}$\pm$\,.007\,$\pm$\,\ \ .0000001
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\noindent
making it among the shortest period non-degenerate systems known.
     
   Our present observations were made on 11, 12 and 14 February 
and 9, 12 May, 1994 at Lowell Observatory, Flagstaff, Arizona.  A 
thermoelectrically cooled EMI 6256S (S-13 cathode) PMT was used in 
conjunction with the 0.78 m National Undergraduate Research 
Observatory reflector.  Approximate coordinates of the variable, 
comparison and the check star are given in Table 1 and are designated
as star 33, d, and c, respectively, on the charts by Kinman et al. (1966).  
About 250 observations were taken in each passband.
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\centerline{Table 1}                          
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\begin{center}
\begin{tabular}{lcc}
\hline                           
           Star      &  R.A. (2000)&        Dec. (2000)\\
\hline
\\              
          EK Com     & 12\fh 51\fmm 20\fss 2 &27\degr 12'57"\\          
          Comparison & 12\fh 51\fmm 55\fss 7 &27\degr 16'17"\\
          Check      & 12\fh 50\fmm 59\fss 2 &27\degr 15'30"\\
\hline
\end{tabular}
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        Five mean epochs of minimum light were determined from the 
observations made during two secondary and three primary eclipses.
The bisection of chords technique was utilized in their determination.
These minima are given in Table 2 accompanied by their probable errors 
in parentheses.  The five precision epochs, along with eight times of low 
light from Kinman et al. (1966), the epoch by Borovicka (1990) and the visual timing by 
Locher (1986) were introduced into a weighted least squares solution 
to obtain a linear ephemeris.  A quadratic ephemeris was also determined.  
In both of these calculations, visual timings and photographic timings given a weight 
of 0.1.  While photoelectric observations were given a weight of 1.0 
with the exception of our last timing which was given a lower weight 
of 0.5.  The improved ephemerides are:
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\hspace*{25mm}
        JD Hel Min. I=2449399.0022 + 0\fd 26668726$\times$E and,\hfill   (2)
\hspace*{7.2cm}$\pm$.0019\ $\pm$\ \ .00000011
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\hspace*{1.5cm}JD Hel Min. I=2449399.0018+0.26668637$\times$E $-$2.05$\times 10^{-11}\times$ E$^2$ \hfill (3)
\hspace*{6cm}$\pm$.0018\,$\pm$\,.00000036 \hspace*{.63cm}$\pm$\ \ .80
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        Figure 1. Photoelectric light curves of EK Com as defined by the 
 individual observations.
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 Figure 2. Period behavior of EK Com as calculated from Equation 2.     
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\centerline{3}
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\centerline{Table 2}
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\begin{tabular}{lcrrr}
\hline
    JD HEL.& & & & \\
    2400000+        &Minimum  &  Cycles& (O$-$C)$_1$  &  (O$-$C)$_2$\\
\hline
\\
    49397.0006(3)    & II &       $-$7.5&   $-$0.0015 & $-$0.0011\\
    49399.0022(5)    & I  &        0.0  &      0.0000 &  0.0004\\
    49482.7440(1)    & I  &      314.0  &   $-$0.0020 &  0.0027\\
    49482.8740(7)    & II &      314.5   &  $-$0.0013 & $-$0.0007\\
    49485.6710(13)   & I  &      325.0   &  $-$0.0002 & $-$0.0038\\
\hline
\end{tabular}
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Equation 2 was used to calculate the (O$-$C)$_1$ residuals in Table 2 
and the phases of the present observations. Equation 3  was 
used to calculate the (O$-$C)$_2$ residuals.  The quadratic term in the second ephemeris is marginally significant and negative.  Because of its small 
magnitude and doubtful significance, we cannot regard this as proof that
the present period behavior of EK Com is dominated by magnetic breaking. 
More timings of minimum light are needed, both from photographic archives 
and future observations.                                     
  
     The B,V light curves of EK Com as defined by their individual 
observations are shown in Figure 1 as differential magnitude 
(variable--comparison) versus phase. The period behavior of the system as calculated  
from the linear ephemeris, equation (1), is shown as Figure 2.
Our preliminary unspotted solution yields a mass ratio of 0.32 and a 
fill-out  of 13\% for this W-type W UMa system.
The analysis of the observations is underway.
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\beginauthors
\authorsrightcol
 Ronald G. SAMEC$^{\star}$,  
 Brian CARRIGAN$^{\star}$ and 
 Eric E. PADGEN$^{\star}$
 Millikin University
 Decatur, IL  62522  USA
\endauthors
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 $^{\star}$Visiting Astronomer, Lowell Observatory, Flagstaff, Arizona, USA

 \references
 
Borovicka, J., 1990, {\it J. AAVSO}, {\bf 19}, 8 

Kinman, T.D., Wirtanen, C.A. and Janes, K. A., 1966, {\it ApJSS}, {\bf 119}, 379

Locher, K., 1986, {\it BBSAG}, No\,79

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