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\input ibvs2.sty

\begin{document}

\IBVShead{5596}{17 January 2005}

\IBVStitle{BVRI observations of EM Cygni in the Years 2003-2004}

\IBVSauth{Spogli, Corrado$^1$; Fiorucci, Massimo$^1$; Capezzali, Daniele$^1$; Mancinelli, Van\-nio$^2$; Nucciarelli, Giuliano$^1$; Brunozzi, Paolo$^2$; Fagotti, Paolo$^2$; Rocchi, Gianni$^2$}

\IBVSinst{Osservatorio Astronomico, Universit\`a di Perugia, Via A. Pascoli I-06100 Perugia, Italy}
\IBVSinst{Gruppo Astrofili Monte Subasio, Piazza Santa Maria 2, Assisi, Italy}


\SIMBADobj{EM Cyg}
\IBVStyp{ UG }
\IBVSkey{photometry}
\IBVSabs{In this paper we report BVRI observations of the dwarf nova}
\IBVSabs{EM Cyg obtained in the years 2003 and 2004. A preliminary}
\IBVSabs{statistical analysis is reported.}


\begintext

The dwarf nova EM Cyg is an eclipsing and spectroscopic binary that belongs 
to the Z Cam class (Downes \& Shara 1993). From the
catalogue of Ritter and Kolb (2003), we know that EM Cyg has V $\simeq$ 13\fmm3 
mag during the regular minimum, V $\simeq$ 14\fmm4 at minimum during the eclipse, 
V $\simeq$ 12\fmm5 during the maximum, and V $\simeq$ 12\fmm9 in standstill. 
We observed EM Cyg since 1997 with the aim to study its variability using
broad band photometry (Spogli et al. 2003). Here we improve our previous
analysis using new $BVR_cI_c$ data obtained during the Summer-Autumn 2003
and 2004, for a total of 57 new nights. 
All photometric new data are reported in Tables 1 and 2.

The observations of EM Cyg were made at the Perugia Astronomical Observatory 
with 0.40 m Automatic Imaging Telescope (Tosti et al. 1996), and at Porziano 
Astronomical Observatory (Assisi) with the 0.35 m Schmidt-Cassegrain telescope
equipped with an HiSIS 23 CCD camera (Kodak Kaf 401E of 762$\times$512 pixel). 
The instruments used and the photometric techniques have been already described 
in Spogli et al. (1998). Both telescopes are endowed with standard 
$BVR_cI_c$ Johnson-Cousins broad-band filters. An inter-comparison between 
results obtained during the same nights shows no relevant systematic difference, 
within the typical standard deviation of each instrument.
All data are obtained in differential photometry using the calibration stars 
reported by Misselt (1996) and Spogli et al. (2003).

Figure 1 shows the V light curve during 2003, and the visual estimates available
from AFOEV ({\tt http://cdsweb.u-strasbg.fr/afoev/}). A similar comparison can be
done with all our database (including Spogli et al. 2003), with the conclusion that 
our multi-band photometry samples very well the outburst, the decline and the 
minimum phases, while there are few data about the rising phase. 
The typical time interval between two outbursts is 23 days, with a range of
15-40 days. The general trend is well characterized, with the emission dominated 
by the secondary star during the minimum ($V-I$ $\simeq$ 1\fmm1, see Figure 2) and by 
the accretion disk during the outburst ($V-I$ $\simeq$ 0\fmm6).
The main photometric informations are summarized in Table 3, taking into account
the new data and the 1997-2000 data (Spogli et al. 2003). 


\newpage

\begin{center}
\centerline{{\bf Table 1} 2003 BVR$_c$I$_c$ data of EM Cyg}
\begin{tabular}{cccccc}
\hline
\hline
UT Date  &JD       & $B$              & $V$           & $R_c$       & $I_c$ \\
&(2450000+) &                &               &             &    \\
\hline
02/06/2003 & 2792.528 & 13.02$\pm$0.05& 12.82$\pm$0.04 &12.49$\pm$0.04& 12.01$\pm$0.04\\
05/06/2003 & 2795.549 & 13.29$\pm$0.13& 12.97$\pm$0.05 &12.65$\pm$0.04& 12.14$\pm$0.03\\
06/06/2003 & 2796.556 & 13.61$\pm$0.12& 13.21$\pm$0.05 &12.79$\pm$0.04& 12.21$\pm$0.03\\
11/06/2003 & 2801.581 & 14.08$\pm$0.05& 13.38$\pm$0.05 &12.93$\pm$0.04& 12.33$\pm$0.03\\
12/06/2003 & 2802.574 & 13.96$\pm$0.05& 13.43$\pm$0.05 &13.02$\pm$0.04& 12.37$\pm$0.03\\
20/06/2003 & 2810.554 & 13.11$\pm$0.05& 12.86$\pm$0.05 &12.58$\pm$0.04& 12.14$\pm$0.03\\
21/06/2003 & 2811.546 & 13.38$\pm$0.07& 13.01$\pm$0.05 &12.65$\pm$0.04& 12.12$\pm$0.03\\
22/06/2003 & 2812.558 & 13.57$\pm$0.08& 13.15$\pm$0.04 &12.74$\pm$0.04& \\
25/06/2003 & 2815.542 & 14.31$\pm$0.07& 13.64$\pm$0.04 &13.08$\pm$0.04& 12.46$\pm$0.04\\
26/06/2003 & 2816.592 & 14.43$\pm$0.08& 13.57$\pm$0.05 &13.04$\pm$0.03& \\
08/07/2003 & 2828.501 & 12.78$\pm$0.09& 12.43$\pm$0.04 &12.13$\pm$0.04& 11.66$\pm$0.04\\
12/07/2003 & 2832.521 & 13.35$\pm$0.07& 13.12$\pm$0.05 &12.77$\pm$0.04& 12.22$\pm$0.04\\
15/07/2003 & 2836.496 & 14.51$\pm$0.05& 13.61$\pm$0.04 &13.09$\pm$0.04& 12.47$\pm$0.04\\
18/07/2003 & 2839.475 & 14.49$\pm$0.10& 13.62$\pm$0.05 &13.13$\pm$0.04& 12.46$\pm$0.04\\
19/07/2003 & 2840.495 & 13.99$\pm$0.11& 13.53$\pm$0.04 &13.04$\pm$0.04& 12.41$\pm$0.04\\
22/07/2003 & 2842.536 & 14.01$\pm$0.09& 13.42$\pm$0.06 &13.12$\pm$0.03& 12.48$\pm$0.04\\
23/07/2003 & 2843.526 & 14.47$\pm$0.11& 13.53$\pm$0.03 &13.04$\pm$0.04&\\
03/08/2003 & 2854.509 & 13.44$\pm$0.06& 12.88$\pm$0.05 &12.54$\pm$0.04& 12.07$\pm$0.04\\
05/08/2003 & 2857.334 &  &  &12.86$\pm$0.05& \\
06/08/2003 & 2858.428 & 14.33$\pm$0.05& & & \\
10/08/2003 & 2862.461 & 14.12$\pm$0.11& & & \\
12/08/2003 & 2864.487 & 14.23$\pm$0.07& 13.49$\pm$0.04 &13.15$\pm$0.04& 12.47$\pm$0.04\\
13/08/2003 & 2865.404 & & 13.68$\pm$0.05 &13.18$\pm$0.04& 12.54$\pm$0.04\\
18/08/2003 & 2870.321 & & 13.57$\pm$0.05 &13.08$\pm$0.05& \\
19/08/2003 & 2871.441 & 14.03$\pm$0.05& 13.51$\pm$0.04 &13.01$\pm$0.04& \\
20/08/2003 & 2872.392 & 14.32$\pm$0.12& 13.83$\pm$0.04 &13.21$\pm$0.05& \\
22/08/2003 & 2874.394 & 14.09$\pm$0.08& 13.51$\pm$0.04 &13.02$\pm$0.05& 12.43$\pm$0.04\\
10/09/2003 & 2893.389 & 12.25$\pm$0.12&  &  & \\
15/09/2003 & 2898.346 & 12.51$\pm$0.09& 12.32$\pm$0.05 & & \\
17/09/2003 & 2900.405 & 12.85$\pm$0.05& 12.53$\pm$0.03 &12.25$\pm$0.04& 11.81$\pm$0.04\\
18/09/2003 & 2901.368 & 12.94$\pm$0.07& 12.68$\pm$0.05 &12.35$\pm$0.05& 11.92$\pm$0.04\\
19/09/2003 & 2902.377 & 13.23$\pm$0.09& 12.84$\pm$0.05 &12.54$\pm$0.05& 12.12$\pm$0.04\\
21/09/2003 & 2904.317 & 13.71$\pm$0.06& 13.20$\pm$0.08 &12.86$\pm$0.05& 12.35$\pm$0.04\\
22/09/2003 & 2905.341 & 14.01$\pm$0.05& 13.31$\pm$0.04 &              &               \\
25/09/2003 & 2908.355 & 13.98$\pm$0.05& 13.28$\pm$0.07 &12.85$\pm$0.07& 12.37$\pm$0.05\\
26/09/2003 & 2909.363 & 13.96$\pm$0.07& 13.41$\pm$0.06 &12.92$\pm$0.06& 12.34$\pm$0.05\\
03/10/2003 & 2916.336 & 13.26$\pm$0.08& 12.76$\pm$0.05 &12.44$\pm$0.05& 12.03$\pm$0.04\\
06/10/2003 & 2919.321 & 13.67$\pm$0.08& 13.21$\pm$0.05 &12.72$\pm$0.05&               \\
10/10/2003 & 2923.331 & 14.04$\pm$0.08& 13.44$\pm$0.05 &12.98$\pm$0.05& 12.43$\pm$0.04\\
12/10/2003 & 2925.307 & 13.91$\pm$0.04& 13.39$\pm$0.05 &              &               \\
16/10/2003 & 2929.396 & 13.23$\pm$0.12& 12.86$\pm$0.05 &12.51$\pm$0.05& 12.09$\pm$0.04\\
27/10/2003 & 2940.271 & 13.56$\pm$0.13& 13.07$\pm$0.05 &12.76$\pm$0.03& 12.21$\pm$0.04\\

\hline
\end{tabular}
\end{center}

\newpage

\begin{center}
\centerline{{\bf Table 2} 2004 BVR$_c$I$_c$ data of EM Cyg}
\begin{tabular}{cccccc}
\hline
\hline
UT Date  &JD       & $B$              & $V$           & $R_c$       & $I_c$ \\
&(2450000+) &                &               &             &    \\
\hline
25/05/2004 & 3150.599 & 13.08$\pm$0.09& 12.74$\pm$0.05 &12.45$\pm$0.04& 12.01$\pm$0.03\\
31/05/2004 & 3156.609 & 13.69$\pm$0.08& 13.31$\pm$0.05 &12.91$\pm$0.05& 12.37$\pm$0.04\\
12/06/2004 & 3168.612 & 13.82$\pm$0.08&                &              &               \\
19/06/2004 & 3175.557 & 13.75$\pm$0.08& 13.24$\pm$0.04 &12.84$\pm$0.04&               \\
06/07/2004 & 3193.394 &               & 12.67$\pm$0.07 &              & 11.94$\pm$0.06\\
15/07/2004 & 3202.384 &               & 13.40$\pm$0.05 &              & 12.33$\pm$0.04\\
16/07/2004 & 3203.379 &               & 13.31$\pm$0.05 &              & 12.37$\pm$0.05\\
17/07/2004 & 3204.379 &               & 13.49$\pm$0.05 &              & 12.36$\pm$0.05\\
22/07/2004 & 3209.487 & 14.04$\pm$0.09&                &              &               \\
23/07/2004 & 3210.395 &               & 13.45$\pm$0.05 &              & 12.34$\pm$0.04\\
30/07/2004 & 3217.413 &               & 13.45$\pm$0.05 &              & 12.31$\pm$0.04\\
01/08/2004 & 3219.498 & 14.09$\pm$0.07&                &              &               \\
17/08/2004 & 3235.441 & 14.45$\pm$0.11& 13.58$\pm$0.05 &13.05$\pm$0.05& 12.42$\pm$0.04\\
18/08/2004 & 3235.514 & 14.38$\pm$0.09& 13.62$\pm$0.05 &13.10$\pm$0.04& 12.50$\pm$0.04\\
21/08/2004 & 3239.444 & 13.89$\pm$0.12& 13.19$\pm$0.07 &12.74$\pm$0.04& 12.22$\pm$0.05\\
22/08/2004 & 3239.571 & 13.93$\pm$0.09& 13.26$\pm$0.04 &12.78$\pm$0.04& 12.24$\pm$0.05\\
08/10/2004 & 3287.418 &               & 12.91$\pm$0.05 &              & 12.16$\pm$0.05\\
23/10/2004 & 3302.404 &               & 13.57$\pm$0.05 &              & 12.35$\pm$0.04\\

\hline
\end{tabular}
\end {center}



\vskip 8mm
\centerline{{\bf Table 3} Photometric characteristics of EM Cyg from our 1997-2004 observations.}
\begin{center}
\begin{tabular}{lcccc}
\hline
\hline
&   $B$          & $V$           & $R_c$       & $I_c$ \\
\hline
Maximum Outburst       & 12.25  & 12.20 & 11.98 & 11.62 \\
Minimum of Light       & 14.51  & 13.83 & 13.24 & 12.65 \\
%                      &        &       &       &       \\
Outburst Amplitude     & 2.2    & 1.5   &  1.1  &  0.9  \\
Decay Rates(mag/day)   & 0.18$\pm$0.06  & 0.14$\pm$0.04  & 0.12$\pm$0.04  & 0.09$\pm$0.04 \\
%                      &                &                &                & \\
 \hline
                       & ($B-V$)          &    ($V-R_c$)   &    ($V-I_c$)   & \\
 \hline
Averages during the outburst & 0.2    &    0.3     &     0.7 & \\
Averages during quiescence   & 0.7    &    0.5     &     1.1 & \\
  \hline
 \end{tabular}
\end {center}

\IBVSfig{9.5cm}{5596-f1.eps}{$V$ light curve of EM Cyg from June 1st to October
27th 2003. Circles represent the data here reported, while small crosses are 
visual estimates available from AFOEV 
({\tt http://cdsweb.u-strasbg.fr/afoev/}).}
\IBVSfigKey{5596-f1.eps}{EM Cyg}{light curve}

\IBVSfig{9.5cm}{5596-f2.eps}{Color-Magnitude diagram for the dwarf nova EM 
Cygni. The diagram contains the data here reported and the previous results 
(Spogli et al. 2003).}
\IBVSfigKey{5596-f2.eps}{EM Cyg}{diagram}


\references

Downes R. A., Shara M. M., 1993, {\it PASP}, {\bf 105}, 127
%%\BIBCODE{1993PASP..105..127D}

Misselt K. A., 1996, {\it PASP}, {\bf 108}, 146
%%\BIBCODE{1996PASP..108..146M}

Ritter H., Kolb U. 2003, {\it A\&A}, {\bf 404}, 301  
%%\BIBCODE{2003A&A...404..301R} 

Spogli C., Fiorucci M., Tosti G., 1998, {\it A\&AS}, {\bf 130}, 485 
%%\BIBCODE{1998A&AS..130..485S}

Spogli C., Fiorucci M., Raimondo G., 2003, {\it IBVS}, 5365
%%\BIBCODE{2003IBVS.5365....1S}

Tosti G., Pascolini S., Fiorucci M., 1996, {\it PASP}, {\bf 108}, 706
%%\BIBCODE{1996PASP..108..706T}

\end{document}


