\documentstyle[epsf]{article}

\input ibvs.sty
%\setlength{\parindent}{0pt}

\def\fp{\hbox{$.\!\!^{\scriptscriptstyle\rm p}$}}

\begin{document}

% Call for macro \IBVShead{Number}{Date} - To be filled by the editors!
\IBVShead{4374}{23 September 1996}     % Use it with dummy or empty a

% Call for macro \title {Title of the paper}
\title{A New Ephemeris for ER Cephei}

\vskip -4mm
% Call for macro \begintext
\begintext

On June 20-22, 1995, two of the authors (RMB and RJH) used the Southeastern Association for Research 
in Astronomy (SARA) 0.9 m telescope at Kitt Peak National Observatory to test 
the newly acquired Axiom Research, Inc., AX-4 CCD camera equipped with a Kodak KAF 4200 (2048 $\times$ 2048) chip. Observations 
of the galactic cluster NGC 188 were made using a Cousins $R$ filter. 
The images were
reduced using the MIRA Image Processing Software, developed by Axiom Research, Inc.  Differential aperture photometry was performed,
resulting in light curves for
ER, ES, EQ Cep, and the variables V5 and V8 defined by Kaluzny \& Shara (1987). 
Our ER Cep light curve is shown in Figure 1. Some intrinsic night-to-night variations appear to be present.  A presentation and 
discussion of all the observations will be forthcoming.
After phasing the ER Cep data using the zero-epoch HJD\,2446696.8432 and period 0.2857299 days listed in Kaluzny (1990), 
we noticed that primary minimum occurred at phase 0\fp 235. This indicated the need to
determine a new ephemeris for ER Cep, which we present in this note.

Using the method of 
Kwee \& van Woerden (1956),
one primary and two secondary minima were determined from our observations. 
We also computed minima from the observations by
Kaluzny \& Shara (1987) and Kaluzny (1990). These are listed in Table 1, together with estimates
for their mean errors. $(O-C)_{1}$ residuals are computed with respect to the Kaluzny (1990) ephemeris. 
The zero-epochs listed in Worden et al. (1978) and Kholopov \& Sharov (1967)
were also added to the list, as well as the minimum by Kholopov \& Sharov (1966).
\vskip -1.9cm
\hspace*{-1.8cm}
\epsfysize=10cm
\centerline{\epsffile{4374-f1.ps}}
\begin{center}
Figure 1. ER Cep differential $R_{\rm C}$  magnitudes observed on June 20 (squares), June 21 (triangles) and June 22 (diamonds), 1995
\end{center}
\vfill \eject

\centerline{2}
\vskip -2cm
\hspace*{-1.8cm}
\epsfysize=7.7cm
\centerline{\epsffile{4374-f2.ps}}
\centerline{Figure 2. $(O-C)_{2}$ diagram for ER Cep}

\vskip 2mm
A weighted linear least squares fit to these minima yields the new ephemeris
\vskip -4mm
\begin{eqnarray}
{\rm Min.}\,{\rm (HJD)}& = & 2446696.84215 + 0.28573616 \times E \\
\ & & \phantom{000000..0}\pm33\phantom{+0.0000.}\pm12 \nonumber
\end{eqnarray}
\vskip -2mm
The residuals, with respect to this ephemeris, are listed as $(O-C)_{2}$ in Table 1 and shown plotted in Figure 2.
The orbital period of ER Cep appears to have
remained secularly constant over the past 30 years. This is unusual given the short period of this moderately late
spectral type [$(B-V)_{0}\approx0\fm74$] 
W-type W UMa binary. 
 
\begin{center}
\centerline{Table 1. Minima for ER Cep}
\vskip 1mm
\begin{tabular}{rcccrl}
\hline
$E\;\;\;$ & $(O-C)_1$ &  HJD & Error & $(O-C)_2$ & Reference \\
\hline
$-$26106.0 & $-0.167\phantom{00}$ & $39237.411\phantom{00}$ & $0.001\phantom{00}$ & $-0.003\phantom{00}$ & Kholopov \& Sharov (1966) \\
$-$26106.0 & $-0.168\phantom{00}$ & $39237.410\phantom{00}$ & $0.001\phantom{00}$ & $-0.004\phantom{00}$ & Kholopov \& Sharov (1967) \\
$-$16525.0 & $-0.114\phantom{00}$ & $41975.043\phantom{00}$ & $0.001\phantom{00}$ & $-0.009\phantom{00}$ & Worden et al. (1978) \\
 $-$917.5  & $-0.00189$ &  46434.68413 &  0.00066 & $\phantom{+}0.00490$ & Kaluzny \& Shara (1987)$^{a}$ \\
 $-$868.5  & $-0.00345$ &  46448.68333 &  0.00081 & $\phantom{+}0.00303$ & Kaluzny \& Shara (1987)$^{a}$ \\
 $-$861.5  & $-0.0126\phantom{0}$ &  $46450.6743\phantom{0}$ &  $0.0012\phantom{0}$ & $-0.0062\phantom{0}$ & Kaluzny \& Shara (1987)$^{a}$ \\
    0.5  & $-0.00004$ &  46696.98603 &  0.00007 & $\phantom{+}0.00101$ & Kaluzny (1990) \\
  276.0  & $-0.00019$ &  46775.70446 &  0.00007 & $-0.00087$ & Kaluzny (1990) \\
  276.5  & $\phantom{+}0.00131$ &  46775.84883 &  0.00058 & $\phantom{+}0.00063$ & Kaluzny (1990)$^{a}$ \\
  286.5  & $\phantom{+}0.00100$ &  46778.70582 &  0.00019 & $\phantom{+}0.00026$ & Kaluzny (1990) \\
  287.0  & $\phantom{+}0.00006$ &  46778.84774 &  0.00031 & $-0.00069$ & Kaluzny (1990)$^{a}$ \\
 11171.0 & $\phantom{+}0.06714$ &  49888.79905 &  0.00028 & $-0.00172$ & this paper \\
 11174.5 & $\phantom{+}0.06819$ &  49889.80016 &  0.00065 & $-0.00069$ & this paper \\
 11178.5 & $\phantom{+}0.0674\phantom{0}$ &  $49890.9423\phantom{0}$ & $0.0012\phantom{0}$ & $-0.0015\phantom{0}$ & this paper \\
\hline
\end{tabular}
\vskip 2mm
$^{a}$ Determined in this paper from observations listed in the reference.
\end{center}

\vskip .2cm

\beginauthors
R.M. BRANLY
Department of Physical Sciences
Broward Community College
Fort Lauderdale, FL 33314, U.S.A.
\vskip 3mm
\authorsrightcol
M.E. BELFORT$^{\star}$, P.A. FRIEND$^{\star}$
W. VAN HAMME
Department of Physics
Florida International University
Miami, FL 33199, U.S.A.
\endauthors
\vskip 2mm

\begin{center}

R.J. HIGGINS

Motorola, Inc.

Radio Products Group Applied Research

Fort Lauderdale, FL 33322, U.S.A.
\end{center}
\vfill \eject

\centerline{3}
\vskip 2mm
{\it Acknowledgment:}
$^{\star}$ Participants in the Research Experience for Undergraduates (REU) program
at Florida International University, sponsored by the National Science Foundation, grant PHY-9531353.


\references
 
Kaluzny, J., 1990, {\it AcA}, {\bf 40}, 61

Kaluzny, J., \& Shara, M.M., 1987, {\it ApJ}, {\bf 314}, 585

Kholopov, P.N., \& Sharov, A.S., 1966, {\it Astr. Circ.}, No.\,377

Kholopov, P.N., \& Sharov, A.S., 1967, {\it Astr. Circ.},  No.\,434

Kwee, K.K., \& van Woerden, H., 1956, {\it Bull. Astr. Inst. Netherlands}, {\bf 12}, 327

Worden, S.P., Coleman, G.D., Rucinski, S.M., \& Whelan, J.A.J., 1978, {\it MNRAS}, {\bf 184}, 33
\end{document}
