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\IBVShead{4234}{28 August 1995}


\title{PRECISION U, B, V, R, I, LIGHT CURVES OF LP CEPHEI}

\begintext

    In our study of the eccentric eclipsing binary (EEB) candidates of Heged\"us
(1988), we obtained UBVRI photoelectric light curves of LP Cephei.  LP Cep 
(HBV 484 = SVS 681) was discovered by Wachmann (1972).  He identified it as 
an Algol type variable, with the secondary displaced to approximately 0.55 
phase.  The paper includes accurate positions, a finder chart, a linear 
ephemeris, and a list of photographic magnitudes.

    Our present observations were made on 21 through 25  (inclusive) 
September, 1994  at Kitt Peak National Observatory, Arizona.  The CCD 
photometer system (CCDPHOT) was used in conjunction with the 0.9m Cassegrain 
reflector telescope.  Approximate coordinates of the variable, comparison, and  
check star are given in Table 1 and are designated as star V, C, and K, 
respectively, on the CCD image taken during observation (Figure 1).  About 400 
observations were taken in each passband.
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\centerline{Table 1}
\begin{center}
\begin{tabular}{lcc}
\hline
                  Star   &          R.\,A.\,(2000)  &   Dec.\,(2000)\\
\hline
\\
               LP Cep     &    21\fh 19\fmm 50\fs  &     60\degr 42' 28''\\
               Comparison &    21\fh 19\fmm 44\fs   &    60\degr 41' 20''\\
               Check     &        21\fh 19\fmm 47\fs &   60\degr 40' 24''\\ 
\hline
\end{tabular}
\end{center}
\vskip 2mm

    Four mean epochs of minimum light were determined from the observations 
made during one 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.   We calculated a 
linear ephemeris using Wachmann's data alone (equation 1) and another 
ephemeris using our data alone (equation 2).  From Wachmann's data we obtained 
\vskip 1mm
\hspace*{25mm}JD Hel. Min I = 2430517.4649 + 0\fd 6930642  $\times$ E \hfill        (1)
\hspace*{8cm}$\pm$8 \hspace*{1.7cm}$\pm$4
\vskip 2mm
\noindent in good agreement with Wachmann's (1972) ephemeris, while our observations 
yielded
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\hspace*{25mm}JD Hel. Min I = 2449621.73239 + 0\fd 693180 $\times$ E \hfill    (2)
\hspace*{8.2cm}$\pm$3 \hspace*{1.6cm}$\pm$7
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\centerline{Table 2}
\begin{center}
\begin{tabular}{lcrr}
\hline
 
            JD Hel.& & & \\
          2400000+      &Minimum   &  Cycle      &  O$-$C\\
\hline
\\
         49617.9199 (11) &   II    &  $-$5.5     &   0.0000\\
         49618.9597 (2)  &    I    &  $-$4.0     &   0.0000\\
         49619.6528 (2)  &    I    &  $-$3.0     &  $-$0.0001\\
         49621.7324 (5)  &    I    &   0.0       & 0.0000\\
\hline
\end{tabular}
\end{center}
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\centerline{2}
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\centerline{\epsffile{4234-f1.ps}}
\begin{center}
Figure 1. CCD field image, showing LP Cep (V), the comparison star (C), and
the check star (K).
\end{center}
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\centerline{\epsffile{4234-f2a.ps}}
\begin{center}
Figure 2a. U, B photoelectric light curves of LP Cep as defined by the 
individual observations.
\end{center}
\vfill \eject

\centerline{3}
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\centerline{\epsffile{4234-f2b.ps}}
\begin{center}
Figure 2b. B, V photoelectric light curves of LP Cep as defined
by the individual observations.
\end{center}
\epsfysize=10cm
\centerline{\epsffile{4234-f2c.ps}}
\begin{center}
Figure 2c. R, I photoelectric light curves of LP Cep as defined
by the individual observations.
\end{center}
\vfill \eject
\centerline{4}
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The linear ephemeris  determined by equation 2 was used to calculate the O$-$C 
residuals and the phases of our present observations.  The calculated periods of
each data set indicate a period increase of $\sim$10 s; however, the large gap 
in timings and the sparsity of the data make it unclear if this period change 
is real.  More timings of minimum light are needed, both from photographic 
archives and future observations, so that the period behavior of the system 
can be determined.
   
 The U, B, V, R, I  light curves of LP Cep as defined by their individual 
observations  are shown in Figure 2 as differential magnitude 
(variable$-$comparison) versus phase.  We have obtained a preliminary solution, which 
indicates that LP Cep is a typical short-period Algol with the secondary 
component filling its Roche lobe and the primary component attaining a fillout 
of $\sim$80\% .  The temperature difference between the components is 
$\sim$2800 K.  Further analysis of the observations is underway.

\vskip 3mm
This work was partially supported  by Millikin University Leighty Funds.

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\beginauthors
\authorsrightcol
 Ronald G. SAMEC$^{\star}$
 Brian J. CARRIGAN$^{\star}$ 
 Richard McDERMITH, and 
 Julie FRENCH            
 Millikin University,                                                                                Decatur, 
IL 62522, USA       
\endauthors

\vskip 3mm
\noindent $^{\star}$ Visiting Astronomer, Kitt Peak National Observatory, 
National Optical Astronomical Observatories, which are operated by the 
Association of Universities for Research in Astronomy, Inc. under contract 
with the National Science Foundation 
\vskip 8mm

\references

Wachmann, A.A., 1972, {\it IBVS}, No.\,749

Heged\"us, T., 1988, {\it Bull. Inform. CDS}, No\,35, 23


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