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\IBVShead{4117}{28 November 1994}      % Use it with dummy or empty arguments

% Call for macro \title {Title of the paper}
\centerline{\ft PHOTOELECTRIC OBSERVATIONS OF THE CLOSE}
\centerline{\ft ECLIPSING BINARY VW CEPHEI}
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    Differential photoelectric photometry of the close eclipsing binary
VW Cephei (SAO\ 9828, M$_v$=7.45$\pm$0.12,  B$-$V=+0.73$\pm$0.20) was carried 
out during  the summer 1993 at the station of Capanne di  Cosola 
(AL, Italy). A total of 473 data points were collected in  the instrumental V 
color.
    
    The comparison star was HIC\,103219 (SAO\,9911, M$_v$=\,6.047$\pm$0.031,
B$-$V=\,+0.934\ $\pm$0.015) and the check one was HIC\,101824 (SAO\,9836,
M$_v$=\,7.076$\pm$0.031, B$-$V=\,+0.934 $\pm$0.015).
    
    Photometry of VW Cephei was carried out with a 200mm 
Schmidt--Cassegrain f15 telescope equipped with a solid state photoelectric 
photometer Optec SSP3 operating in the Johnson--Morgan B and V bands.
    
    Five heliocentric times of minimum were computed using the available
observations. The heliocentric times of minimum obtained with the Minimum Entropy
SOP method (MEMSOP, Gaspani 1993a) are listed in Table 1.
The O$-$C residuals  computed with respect to the ephemeris (Navratil, 
1994):
\vskip 2mm
\hspace*{30mm}{T$_{min}$ (HJD) = 2448862.5255 + 0\fd 27831460$\times$E \hfill (1)
\vskip 2mm
\noindent are listed in the same table. It is interesting to remark that all the residuals are systematically
negative. This means that the ephemeris (1) must be updated in order to satisfy
our data.

    On the other hand the moments of minima observed by Abbott et al. (1994)
as well as Vink\'o et al. (1993) give as yet negative residuals of 
comparable magnitude with respect to the ephemeris (1).

Therefore we computed an updated ephemeris making use of our data
 as well as the recent data of Navratil (1994), Abbott et al. (1994)
 and Vink\'o et al. (1993) in order to increase the accuracy of the
 least squares fit.
 
     On the basis of the available times we obtained the following
 least squares fit:
\vskip 2mm
                                    
\hspace*{30mm}Min.I (HJD)= 2448862.5220 + 0\fd 2783076$\times$E \hfill (2)
\hspace*{69mm}$\pm$               0.0026 $\pm$\ 0.0000024
\vskip 2mm

Table 2 shows the residuals computed with respect to the 
ephemeris (2).

    VW Cephei is an active close binary whose light curve shows temporal 
changes. This variability has been interpreted as arising from the presence
of dark starspots located mainly on the photosphere of the more
massive star of the system (Bradstreet and Guinan, 1990).

    After these premises, it seems to be useful to try to recover the 
true light curve from the noisy data in order to show changes in the 
height of the maxima, depth of the minima and photometric perturbations.

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\centerline{2}
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\centerline{\epsffile{4117-f1.ps}}
\centerline{Figure 1. Light curve of VW Cephei. The solid line is the signal restored}
\centerline{with the optimum Wiener filter and the squares are the individual data points.}
\vskip 3mm
\centerline{Table 1. Heliocentric times of minimum}
\vskip 1mm
\begin{center}
\begin{tabular}{llcl}
\hline
        Observed Minima    &  E    &\ \ \ \ O$-$C& \\
\hline
\\
     2449186.479 $\pm$0.003&     1164  &    $-$0.005 &   (Min.I)\\
     2449191.479 $\pm$0.008&     1182  &    $-$0.014 &   (Min.I)\\
     2449192.457 $\pm$0.006&     1185.5&    $-$0.010 &   (Min.II)\\
     2449192.604 $\pm$0.005&     1186  &    $-$0.003 &   (Min.I)\\
     2449193.42\ \,\ $\pm$0.02 &     1189  &    $-$0.022 &   (Min.I)\\
\hline
\end{tabular}
\end{center}
\vskip 3mm
    In order to recover a convenient estimate of the true signal from
the  noisy  data  we  processed  the  noisy phased data with a signal
restoration  technique  based  on the Optimum  Wiener  Filter  Theory
(Gaspani, 1993b).

Figure 1 shows the restored light curve, graphed as a solid 
line across the original data points and Table 3 shows the results 
obtained.

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\centerline{3}

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\centerline{Table 2. Residuals from the ephemeris (2).}
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%\hbox to 12.5cm {
\begin{center}
\begin{tabular}{rcrc}
\hline
         Epoch&    Observed time &   Residual&    Source\\
           E\ \ \ \ &     of minimum  &     (O$-$C)& \\
                 &  JD 2440000+& & \\
  \hline
  \\
         $-$7.5&      8860.438 &        0.002 &     (a)\\
         $-$0.5&      8862.386 &        0.002 &     (a)\\
          0.0 &     8862.525   &      0.003   &   (a)\\
              &                &              & \\
       1161.0 &     9185.637   &     $-$0.001 &     (b)\\
       1164.0 &     9186.479   &      0.006   &   (c)\\
       1164.5 &     9186.614   &      0.003   &   (b)\\
       1165.0 &     9186.750   &     $-$0.001 &     (b)\\
              &                &              & \\
       1182.0&      9191.479   &     $-$0.003 &     (c)\\
       1185.5&      9192.457   &      0.001   &   (c)\\
       1186.0&      9192.604   &      0.008   &   (c)\\
       1189.0&      9193.420   &     $-$0.011 &     (c)\\
             &                 &              & \\
       1261.0&      9213.465   &     $-$0.004 &     (d)\\
       1401.0&      9252.431   &     $-$0.001 &     (d)\\
       1404.5&      9253.405   &      0.000   &   (d)\\
\hline
\end{tabular}
\end{center}
\vskip 2mm
 (a) Navratil (1994), (b) Abbott et al. (1994),
 (c) Aluigi et al. (present paper), (d) Vink\'o et al. (1993)
\vskip 4mm
\centerline{Table 3}
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%\hbox to 12.5cm {
\begin{center}
\begin{tabular}{lc}
\hline
 &Delta V\\
 &(VW Cep$-$HIC\,103219)\\
\hline
\\
Primary Minimum&$-$1.748\\
Maximum I&$-$1.367\\
Secondary Minimum&$-$1.630\\
Maximum II&$-$1.380\\
\hline
\end{tabular}
\end{center}

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% Call for macros \authors - \authorsrightcol - \endauthors
\beginauthors
Marco ALUIGI                               
GEOS - 3, Promenade Venezia,               
F-78000 Versailles (France)               
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\authorsrightcol
Gianni GALLI
GEOS - 3, Promenade Venezia, 
F-78000 Versailles (France) 
\endauthors
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\centerline{Adriano GASPANI}
\centerline{Osservatorio Astronomico di Brera}
\centerline{Via Brera 28, Milano (Italy), and}
\centerline{GEOS - 3, Promenade Venezia,}
\centerline{F-78000 Versailles (France)}
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\centerline{4}

% Call for macro \references
\references

Abbott, B. Rumignani, D., 1994, {\it Inf. Bull. Var. Stars}, No.\,4041

Bradstreet D., Guinan, E., 1990 in "Active Close Binaries", ed.
    C. Ibanoglu, pag. 467

Gaspani, A., 1993a, "The algorithms useful in finding the extrema of
    the light curves". Talk presented to the Second GEOS Workshop on the
    Eclipsing  Variable  Stars  and their Data Processing", S.Pellegrino
    Terme (Italy), 1993, 21-22 May

Gaspani, A., 1993b, "The processing and the restoration of the light
    curves". Talk presented to the Second GEOS Workshop on the Eclipsing
    Variable Stars and their Data Processing", S.Pellegrino Terme (Italy),
    1993, 21-22 May

Navratil M., 1994, {\it Inf. Bull. Var. Stars}, No.\,3997

Vink\'o, J., G\'al, J., Szatm\'ary, K., Kiss, L. 1993, {\it Inf. Bull. Var. Stars}, 
    No.\,3965

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