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\IBVShead{5240}{20 February 2002}

\IBVStitle{{\large \boldmath ${\rm BV(RI)_C}$} observations of some dwarf novae}


\IBVSauth{Spogli, C.$^1$; Fiorucci, M.$^1$; Tosti, G.$^1$; Nucciarelli, G.$^1$;  Giretti, A. M.$^1$; \break Monacelli, G.$^2$; Macchia, E.$^2$}

\IBVSinst{Observatorio Astronomico, Universit\'a di Perugia, Via A. Pascoli
I-06100 Perugia, Italy}
\IBVSinst{Associazione Astronomica Umbra, Via Ilci 7, Todi, Italy}

\begintext
Dwarf Novae (DN) are erupting cataclysmic variable stars. The 2-6 mag
outbursts last from few days to more than a month and the recurrence times can
be as short as a few days and as long as 30 years (see e.g. Warner 1995).
According to differences in their outburst light curves, they are divided into
three sub-groups, the U Gem stars (UG), the SU UMa stars (SU) and Z Cam stars (ZC).
The U Gem systems have normal outbursts which last a few days to weeks.
In SU UMa systems, except for normal outbursts, there
are so-called superoutbursts which last weeks and occur more regularly
than the normal ones. In Z Cam systems, during decline from some outbursts,
so-called standstills are observed in which the systems stay at a
brightness level somewhat below maximum for a prolonged interval of time,
before returning to quiescence. 
 
In this brief paper we present a sample of photometric $B$, $V$, $R_C$, $I_C$
observations of dwarf novae made in the years
1993-1997  with the 0.40 m Automatic Imaging Telescope at the Perugia
Astronomical Observatory (Tosti et al. 1996). The telescope is mainly devoted
to the monitoring of a large sample of blazars (Fiorucci and Tosti 1996),
however, a fraction of  the telescope time is dedicated to the photometric
observations of DNe.  The instruments used and the photometric techniques have
been already described in Spogli et al. (1998). Part of the data were elaborated by 
the Associazione Astronomica Umbra, using the usual IRAF photometric packages. 
For many DNe we used the calibration stars reported in Misselt (1996), moreover 
we calibrated them with the $I_C$ filter, by observing, on photometric nights,
several standard stars (Landolt, 1992) having ($B-V$) from $-0\fmm2$ to 
$1\fmm4$ over a
wide range of airmass.  The same Landolt stars were used to compute the
standard magnitude for the other DNe during the photometric nights.

The data (Table 1) were obtained during the years in which
we worked to automatize the telescope. Sometimes
the weather conditions varied suddenly  or the telescope blocked and therefore,
in some cases observations exist only in one filter or in some of the filters. 
However, these data are always important since,
joined to other photometric observations, can be used to draw the 
historical light curve. 

The dwarf novae selected have been observed in different phases of 
luminosity: some of them were in outburst, others at minimum. 
For some dwarf novae, that were in outburst at the 
time of the observations, we calculated the spectral slope $\alpha$ (see table 2)
using the same procedure used in Spogli et al. (1998), neglecting interstellar reddening.

\vskip 15mm

{\small 
\centerline{{\bf Table~1}: $BV(RI)_C$ magnitudes of some Dwarf Novae}
\begin{center}
\begin{tabular}{cccccccc}
\hline
\hline
 Name  &Type& Date  & JD         & $B$              & $V$           & $R_C$       & $I_C$ \\
       &       & UT & (2449000+) &                &             &             &    \\
\hline
KW And  & UG  & 95/09/29 & 990.816 & & & 17.3$\pm$0.3 & \\
RX And   & ZC  & 94/10/18 & 644.405 &  & 13.50$\pm$0.05  &  &  \\ 
       &  &94/10/30 & 657.476 & 11.45$\pm$0.05&11.24$\pm$0.05&11.09$\pm$0.05& 9.87 $\pm$0.02\\ 
        &  &94/11/04 & 662.426 & 11.29$\pm$0.09&11.15$\pm$0.05&11.13$\pm$0.05&10.95$\pm$0.03\\  
        &  &94/11/04 & 662.441 & 11.25$\pm$0.08&11.17$\pm$0.05&11.12$\pm$0.05&10.91$\pm$0.02\\
        &  &94/12/15 & 703.341 & 12.23$\pm$0.08&12.21$\pm$0.05&12.05$\pm$0.05&11.71$\pm$0.02\\
AK Cnc &   & 95/01/12 & 729.555 & & & 15.82$\pm$0.08 & \\
             & UG &95/02/02 & 750.434 &    &15.92$\pm$0.08 &15.77$\pm$0.07&15.51$\pm$0.06\\
YZ Cnc& SU &95/01/12 & 729.621 & 13.11$\pm$0.06&13.21$\pm$0.06&13.35$\pm$0.06&13.13$\pm$0.05\\
SS Cyg & UG  &94/10/18&644.362 &  & 12.24$\pm$0.05 & & \\
       &     &94/11/09&667.239 & & 12.51$\pm$0.05 & &\\ 
V503 Cyg& UG &95/07/06 & 905.497 & & &14.69$\pm$0.07& \\
V516 Cyg& UG &97/07/06&1636.552 &               & 17.2$\pm$0.3   &16.9$\pm$0.2  &16.7$\pm$0.2\\
         & &97/08/06&1667.527 & 15.04$\pm$0.13&15.17$\pm$0.09&14.69$\pm$0.06&14.68$\pm$0.08\\
         & &97/08/15&1676.461 &               &16.7$\pm$0.3   &16.5$\pm$0.2  &15.52$\pm$0.07\\
         & &97/08/19&1680.449 & 15.84$\pm$0.12&14.93$\pm$0.09&14.91$\pm$0.08&14.43$\pm$0.06\\
         & &97/08/21&1682.441 &               &17.8$\pm$0.3  &16.7$\pm $0.3 &16.3$\pm$0.2\\ 
         & &97/08/31&1692.455 &               &16.4$\pm$0.2  &16.1$\pm$0.2  &15.75$\pm$0.07\\
         & &97/09/01&1693.437 &               &16.3$\pm$0.2  &15.88$\pm$0.09&15.08$\pm$0.07\\
         & &97/09/02&1694.421 & 13.98$\pm$0.09&13.81$\pm$0.04&13.71$\pm$0.09&13.69$\pm$0.08\\ 
V542 Cyg& UG & 95/07/06 & 905.525 & & &16.4$\pm$0.2&\\
V792 Cyg& UG &95/07/01 & 900.562 & & &15.85$\pm$0.09&\\
V811 Cyg& UG &95/07/01 &900.585 & & &16.1$\pm$0.2&\\  
         & &95/07/13&912.495 & &15.24$\pm$0.08 &15.03$\pm$0.05&14.88$\pm$0.06\\
        & &95/07/16& 915.556 &               &15.71$\pm$0.07 &15.32$\pm$0.06&15.33$\pm$0.07\\   
        & &95/07/21 & 920.506 & & &15.71$\pm$0.05&\\
        & &95/08/03 & 932.435 & & &15.18$\pm$0.05&\\  
        & &95/09/29& 990.648 &               &17.2$\pm$0.3   &16.4$\pm$0.2  &16.1$\pm$0.2\\
 V823 Cyg& UG  &95/07/23 & 912.517 & & & 14.96$\pm$0.08&\\
V1006 Cyg& UG &95/08/03& 932.443 & &&16.1$\pm$0.2&\\
V1028 Cyg& UG &95/08/03& 932.465 & 13.65$\pm$0.08&13.86$\pm$0.05&13.76$\pm$0.07&13.69$\pm$0.06\\
V1251 Cyg& UG & 95/09/27& 988.754 & &&15.01$\pm$0.08&\\
V1316 Cyg& SU &95/07/01&900.602 &               &17.3$\pm$0.3   &16.5$\pm$0.2  &16.3$\pm$0.2\\
        & &95/07/16&915.478 & 16.4 $\pm$0.3 &16.3 $\pm$0.2 &16.1 $\pm$0.1 &15.92$\pm$0.06\\
        & &95/08/23& 953.321 &               &16.1$\pm$0.09  &15.84$\pm$0.08&15.34$\pm$0.04\\
V1390 Cyg& SU &95/07/16& 915.568 &               &16.6$\pm$0.2   &15.86$\pm$0.09&15.13$\pm$0.07\\
V1504 Cyg& SU &95/07/21& 920.543 & & &14.38$\pm$0.06&\\
U Gem  & UG   & 93/02/03& 022.361  & & 14.45$\pm$0.05 & & \\
       &    &93/03/17 & 064.331 & &14.30$\pm$0.07  & & \\
       &    &93/12/30 & 352.367 & & 11.44$\pm$0.05 & & \\
       &    &94/11/17 & 674.592 & & 14.18$\pm$0.05 & & \\
AH Her & ZC &94/04/28&470.449 & 13.97$\pm$0.09&13.80$\pm$0.05&13.57$\pm$0.05&13.01$\pm$0.03\\
         & &94/04/29&471.432 & 13.66$\pm$0.09&13.38$\pm$0.04&13.04$\pm$0.04&12.75$\pm$0.03\\
         & &94/05/01&473.466 & 12.67$\pm$0.09&12.56$\pm$0.05&12.39$\pm$0.04&12.26$\pm$0.03\\
         & &94/05/15&488.467 & 13.91$\pm$0.08&              &13.41$\pm$0.04&13.07$\pm$0.04\\
         & &94/05/21&494.513 & 12.87$\pm$0.07&12.62$\pm$0.05&12.45$\pm$0.04&12.27$\pm$0.03\\
         & &94/06/02&506.377 & 13.41$\pm$0.12&13.36$\pm$0.06&13.07$\pm$0.05&12.86$\pm$0.05\\
         & &94/06/06&510.457 & 12.71$\pm$0.07&12.23$\pm$0.08&11.84$\pm$0.04&11.72$\pm$0.03\\
         & &94/06/16&520.407 & 13.80$\pm$0.10&13.76$\pm$0.05&13.33$\pm$0.04&12.80$\pm$0.04\\
         & &94/06/17&521.475 &               &14.22$\pm$0.05&13.84$\pm$0.04&13.32$\pm$0.03\\
         & &94/06/19&523.451 & 14.68$\pm$0.09&14.12$\pm$0.05&13.64$\pm$0.05&13.15$\pm$0.04\\
         & &94/06/20&524.444 & 14.35$\pm$0.14&14.14$\pm$0.05&13.58$\pm$0.04&              \\
         & &94/06/22&526.383 & 14.56$\pm$0.09&14.10$\pm$0.05&13.64$\pm$0.04&13.16$\pm$0.03\\
         & &94/06/24&528.436 & 12.42$\pm$0.09&12.28$\pm$0.06&12.24$\pm$0.04&              \\
         & &94/06/30&534.385 & 14.54$\pm$0.07&13.92$\pm$0.05&13.55$\pm$0.04&13.17$\pm$0.04\\ 
\hline
\end{tabular}
\end{center}
}

\newpage

{\small 
\vskip 25mm
\centerline{{\bf Table~1}: (continued)}
\begin{center}
\begin{tabular}{cccccccc}
\hline
\hline
Name & Type & Date  & JD         & $B$              & $V$           & $R_C$       & $I_C$ \\
     &         & UT & (2449000+) &                &             &             &    \\
\hline
PR Her &  UG &95/06/30&  899.398 & &&15.17$\pm$0.08&\\
V611 Her&  UG & 95/06/30 & 899.367 & &&16.8$\pm$0.3&\\
V632 Her&  UG & 95/06/30 & 899.437 & &&16.4$\pm$0.2&\\
T Leo   & SU &95/02/02& 750.628 &                &15.95$\pm$0.09 &15.81$\pm$0.09&15.22$\pm$0.07\\
RZ LMi  & UG &95/02/02& 750.568 &                &15.16$\pm$0.08 &15.04$\pm$0.06&14.95$\pm$0.04\\
IR Lyr& UG & 95/06/30 & 899.553 & &&15.19$\pm$0.08&\\
V415 Lyr& UG:  & 95/06/30 & 899.598 &&& 16.5$\pm$0.2&\\
V419 Lyr& ZC & 95/06/30 & 899.588 & &&15.43$\pm$0.08&\\
BI Ori&  UG & 94/12/01  & 729.481 & & &16.2$\pm$0.1 &\\
         & &95/01/16& 733.431 &                &15.69$\pm$0.06 &15.56$\pm$0.05&15.27$\pm$0.06\\
CZ Ori  & UG &93/01/27&043.462 & 13.74$\pm$0.08&13.38$\pm$0.05&13.69$\pm$0.03&              \\      
         & &94/01/12&394.491 &  & 14.65$\pm$0.08 & & \\
         & &94/01/18&400.455 &  &15.07$\pm$0.09 & & \\
         & & 94/10/14& 640.538 & & & 16.1$\pm$0.1 &\\
         & &94/10/22&649.508 &  &12.87$\pm$0.05 & & \\
         & &94/10/27&654.494 &                &15.99$\pm$0.08 &15.52$\pm$0.05&14.59$\pm$0.05\\
         & &94/11/17&675.589 &                &15.46$\pm$0.07 &15.21$\pm$0.05&14.53$\pm$0.05\\
         & &94/12/02&690.403 & 13.14$\pm$0.08&13.19$\pm$0.05&13.06$\pm$0.05&12.77$\pm$0.05\\
         & &95/01/12&729.461 & 15.11$\pm$0.09&15.28$\pm$0.05&15.02$\pm$0.05&14.35$\pm$0.05\\
         & &95/01/16&733.329 & & &15.75$\pm$0.07 &\\   
         & &95/02/02&750.399 & 16.3 $\pm$0.2 &15.99$\pm$0.08&15.52$\pm$0.05&14.35$\pm$0.05\\
         & &95/09/27&988.981 & 13.39$\pm$0.06&13.43$\pm$0.05&13.33$\pm$0.05&13.04$\pm$0.05\\
         & &95/09/29&990.931 & 14.52$\pm$0.07&14.65$\pm$0.05&14.39$\pm$0.05&13.87$\pm$0.05\\
         & &96/12/03&1421.565 &               &15.89$\pm$0.07 &15.39$\pm$0.04&14.69$\pm$0.04\\
         & &96/12/04&1422.417 &               &15.74$\pm$0.06 &15.29$\pm$0.04&14.42$\pm$0.04\\
         & &96/12/05&1423.437 &               &15.57$\pm$0.05 &15.13$\pm$0.04&14.51$\pm$0.04\\
RU Peg & UG &94/10/18&644.365 & & 12.65$\pm$0.05 & & \\       
KT Per & ZC &94/10/18&644.396 & &14.71$\pm$0.05 & &\\
NS Per&  UG & 95/09/27  & 988.933 & & &17.2$\pm$0.3 &\\
PU Per&  UG & 95/09/29  & 990.859 & & &17.1$\pm$0.3 &\\
PY Per  & ZC &95/01/12&729.431 & 14.09$\pm$0.08&14.01$\pm$0.06 &14.21$\pm$0.06&13.56$\pm$0.06\\
        & &95/01/16&733.254 & &15.18$\pm$0.09 &15.07$\pm$0.06&14.88$\pm$0.06\\                
        &  & 95/09/27  & 988.923 &  & &16.1$\pm$0.2&\\    
TZ Per& ZC & 94/10/13  & 639.569 & &&14.29$\pm$0.05&\\
        & &94/10/18& 644.415 & 13.43$\pm$0.07&13.22$\pm$0.05&12.97$\pm$0.05&12.74$\pm$0.05\\
        & &94/10/18& 644.536 & 13.45$\pm$0.06&13.17$\pm$0.05&12.98$\pm$0.05&12.77$\pm$0.05\\
        & &95/01/16& 733.345 & 12.93$\pm$0.06&12.61$\pm$0.05&12.58$\pm$0.05&12.28$\pm$0.05\\
FY Vul  & ZC &95/08/23& 953.298 & 14.24$\pm$0.08&13.99$\pm$0.05&13.71$\pm$0.05&13.43$\pm$0.05\\
\hline
\end{tabular}
\end{center}
}

\vskip 8mm
\centerline{
{\bf Table 2}: The spectral slope of some Dwarf Novae}
\begin{center}
\begin{tabular}{c c c c}
\hline
\hline
Name &Type &JD(2449000+) &$\alpha$ \\
\hline
RX And &ZC &662.426  & 0.4$\pm$0.1 \\
YZ Cnc &SU &729.621 & 0.9$\pm$0.1\\
V516 Cyg& UG&1694.421  &0.4$\pm$0.1\\
V1028 Cyg&UG &932.465 &0.9$\pm$0.2\\
AH Her&ZC &473.466 &0.2$\pm$0.1\\
CZ Ori&UG &690.403 &0.3$\pm$0.2\\

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

\newpage

\references

Fiorucci, M., Tosti, G., 1996, {\it A\&AS}, {\bf 117}, 475

Landolt A.U., 1992, {\it AJ}, {\bf 104}, 340 

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

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

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

Warner B., 1995, {\it ``Cataclysmic Variable Stars''}, Cambridge University Press, 
Cambridge 

\end{document}
