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\begin{document}
\IBVShead{5253}{8 April 2002}

\IBVStitle{{\large ${\mathbf{BV(RI)_C}}$} observations of FY V\lowercase{ul}}

\IBVSauth{Spogli, Corrado$^1$; Fiorucci, Massimo$^1$; Nucciarelli, Giuliano$^1$; Tosti, Gino$^1$; Raimondo, Gabriella$^2$; Macchia, Enrico$^3$; Monacelli, Giuseppe$^3$}

\IBVSinst{Osservatorio Astronomico, Universit\`a di Perugia, Via A. Pascoli
I-06100 Perugia, Italy}
\IBVSinst{Teramo Astronomical Observatory, Collurania, Teramo, Italy}
\IBVSinst{Societ\'a Astronomica Umbra, via Ilci 7, Todi, Italy} 

\SIMBADobj{FY Vul}
\IBVStyp{ UGZ }
\IBVSkey{photometry}
\IBVSabs{In this paper we report BVRI observations of the dwarf nova}
\IBVSabs{FY Vul during low-amplitude variations.}


\begintext

FY Vul is  a poorly known dwarf nova (DN) of the Z Cam subtype, characterized 
by a typical interval time between two subsequent outbursts of 30-50 days
(Richter, 1961). The star varies between $B$=13\fmm4 to $B$=15\fmm3 (Downs and
Shara,  1993). First photometric studies were made by Meinunger (1965), while
Bruch  (1984) reported the color index of the variable: ($U-B$)=$-$0\fmm65 and
($B-V$)=0\fmm53. Spectroscopic observations were taken by Downes et al. (1995):
they revealed H$\alpha$ in emission, while H$\beta$ and H$\gamma$ are in 
absorption with an emission core. Although, the spectrum is typical of a dwarf
nova near the end of an outburst and it confirms the DN classification for the 
object, the overall variability is less than 2 magnitudes.

In this paper we report photometric observations of FY Vul obtained at the Teramo 
Astronomical Observatory of Collurania in August-September 1998, and at the
Perugia Astronomical Observatory in July-August 2001. 
The first series of observations were taken with the 0.72 m Ritchey-Chretien
reflector of Collurania, equipped with a Tektronix 512 CCD camera and $B$, $V$
(Johnson), $R_C$, $I_C$ (Cousins) filters: the data are reported in Table~1.
The photometric techniques used have already been described in two parallel 
papers about V503 Cyg (Spogli et al. 2000a) and V516 Cyg (Spogli et al. 2000b).
The standard magnitudes of the comparison stars are reported by Misselt 
(1996), additionally, we calibrated the standard magnitudes of some of these stars
with the $I_C$ filter: 
$I_C$(2)=13\fmm24$\pm$0\fmm04, $I_C$(3)= 12\fmm96$\pm$0\fmm04, $I_C$(4)=13\fmm82$\pm$0\fmm04, 
$I_C$(5)= 13\fmm99$\pm$0\fmm04, and $I_C$(11)=13\fmm13$\pm$0\fmm04. 

\vskip 0.4cm

\centerline{Table~1: $BV(RI)_C$ magnitudes of FY Vul in August-September 1998}
\vskip 3mm
\begin{center}
\begin{tabular}{cccccc}
\hline
\hline
Date & JD (2451000+) &$B$        & $V$       &      $R_C$     &       $I_C$        \\
\noalign{\smallskip}
\hline
\noalign{\smallskip}
 30/08/1998 & 56.385 & 15.11$\pm$0.08 & 14.76$\pm$0.05 & 14.47$\pm$0.04 & 14.23$\pm$0.04\\
 31/08/1998 & 57.368 & 14.98$\pm$0.05 & 14.66$\pm$0.04 & 14.31$\pm$0.04 & 14.10$\pm$0.04\\
 01/09/1998 & 58.351 & 14.89$\pm$0.05 & 14.52$\pm$0.04 & 14.28$\pm$0.04 & 13.99$\pm$0.04\\
 02/09/1998 & 59.355 & 14.83$\pm$0.06 & 14.50$\pm$0.04 & 14.21$\pm$0.04 & 13.97$\pm$0.04\\
\hline
\end{tabular}
%inserire commenti o note
\end{center}
\vskip 0.4cm

We observed FY Vul in July-September 2001 with the 0.40 m Automatic
Imaging Telescope at the Perugia University Observatory. The equipment used
and the procedures of data analysis have already been described in Spogli et al. 
(1998). The $BV(RI)_C$ data collected are reported in Table 2.

\vskip 3mm

\centerline{Table~2: $BV(RI)_C$ magnitudes of FY Vul in July-September 2001}
\vskip 3mm
\begin{center}
\begin{tabular}{cccccc}
\hline
\hline
Date &JD       & $B$              & $V$           & $R_C$       & $I_C$ \\
 &(2451000+) &                &               &             &    \\
\hline
  15/07/01 &1106.589& 14.65$\pm$0.08& 14.19$\pm$0.02& 14.01$\pm$0.03& 13.59$\pm$0.04\\
  17/07/01 &1108.551& 14.88$\pm$0.03& 14.25$\pm$0.01& 14.72$\pm$0.02& 13.91$\pm$0.04\\
  22/07/01 &1113.517& 14.79$\pm$0.13& 14.61$\pm$0.05& 14.29$\pm$0.06& 13.74$\pm$0.04\\
  23/07/01 &1114.479& 14.77$\pm$0.11& 14.49$\pm$0.03& 14.26$\pm$0.07& 13.97$\pm$0.04\\
  24/07/01 &1115.469& 14.85$\pm$0.08& 14.59$\pm$0.07& 14.26$\pm$0.03& 13.97$\pm$0.04\\
  27/07/01 &1118.480& 14.74$\pm$0.09& 14.47$\pm$0.06& 14.27$\pm$0.03& 13.92$\pm$0.04\\
  28/07/01 &1119.541& 14.71$\pm$0.09& 14.34$\pm$0.06& 14.14$\pm$0.04& 13.57$\pm$0.04\\
  04/08/01 &1126.415& 14.22$\pm$0.12& 14.09$\pm$0.04& 13.92$\pm$0.04\\
  05/08/01 &1127.406& 14.55$\pm$0.13& 14.13$\pm$0.07& 14.08$\pm$0.05\\
  06/08/01 &1128.413& 14.52$\pm$0.13& 14.39$\pm$0.05& 14.25$\pm$0.05& 13.83$\pm$0.04\\
  09/08/01 &1131.408& 14.81$\pm$0.08& 14.62$\pm$0.04& 14.39$\pm$0.03& 14.06$\pm$0.04\\
  11/08/01 &1133.414& 14.79$\pm$0.11& 14.38$\pm$0.03& 14.15$\pm$0.05& 13.88$\pm$0.04\\
  12/08/01 &1134.413& 14.58$\pm$0.04& 14.39$\pm$0.03& 14.09$\pm$0.07& 13.93$\pm$0.04\\
  13/08/01 &1135.562& 14.63$\pm$0.08& 14.43$\pm$0.03& 14.26$\pm$0.07& 13.88$\pm$0.04\\
  14/08/01 &1136.395& 14.65$\pm$0.07& 14.37$\pm$0.05& 14.11$\pm$0.05& 13.88$\pm$0.04\\
  18/08/01 &1140.389& 14.15$\pm$0.09& 13.94$\pm$0.05& 13.71$\pm$0.04& 13.49$\pm$0.04\\
  19/08/01 &1141.419& 14.28$\pm$0.07& 13.97$\pm$0.05& 13.85$\pm$0.04\\
  20/08/01 &1142.366& 14.32$\pm$0.07& 14.05$\pm$0.05& 13.85$\pm$0.04& 13.64$\pm$0.04\\
  21/08/01 &1143.421& 14.32$\pm$0.09& 14.16$\pm$0.05& 13.94$\pm$0.04& 13.66$\pm$0.04\\
  27/08/01 &1149.443& 14.87$\pm$0.06& 14.45$\pm$0.06& 14.23$\pm$0.04& 13.92$\pm$0.04\\
  28/08/01 &1150.382& 14.64$\pm$0.14& 14.44$\pm$0.07& 14.23$\pm$0.06& 13.74$\pm$0.04\\
  12/09/01 &1165.328& 14.83$\pm$0.13& 14.55$\pm$0.09& 14.32$\pm$0.07& 14.09$\pm$0.05\\
\hline
\end{tabular}
%inserire commenti o note
\end {center}
\vskip 0.4cm

The light curve (see Figure 1) seems to show quasi-periodic variation with a period 
of $\sim$ 15-20 days, and a full amplitude of $\sim$ 0.7 mag. Probably FY Vul was 
in a long phase of standstill, but it is not excluded in a previously
unrecognized group of low-amplitude dwarf novae (see Kato et al. 1999). 
Table 3 resumes the main photometric characteristics of the variable during this phase.


\vskip 0.4cm
\centerline{Table~3: Photometric characteristics of FY Vul in July-September 2001}
\vskip 3mm
\begin{center}
\begin{tabular}{lcccc}
\hline
\hline
                  &   $B$            &       $V$      &       $R_C$      &  $I_C$ \\   
\hline     
 Maximum  & 14.15        &   13.94    &    13.71          & 13.57 \\
 Minimum   & 14.88        &   14.62    &    14.49          & 14.09 \\
  & & & & \\ 
\hline
Mean color  index &  ($B-V$)         &   ($V-R_C$)   & ($R_C-I_C$)    &   ($V-I_C$)      \\
                                             &   0.29         &    0.18       &  0.33      &     0.51     \\
\hline
\end{tabular}
%inserire commenti o note
\end {center}
\vskip 0.4cm

To study the behavior of the optical continuum of FY Vul, we computed the 
spectral index $\alpha$ using the same procedure used in Spogli et al. (1998), 
neglecting interstellar reddening.
We find that in this phase the spectral distribution is probably dominated by the 
emission of the secondary star. However, more observations are needed to 
clarify the nature of this interesting object.


\IBVSfig{9cm}{5253-f1.eps}{Light curve of FY Vul. Dashed line
connects consecutive points by natural cubic spline after rendering the
data monotonic}


\references

Bruch, A., 1984, {\it  A\&AS}, {\bf 56}, 441

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

Downes, R., Hoard, D. W., Szkody, P., Wachter, S., 1995, {\it AJ}, {\bf 110},
1824

Kato T., Nogami D., Baba H., 1999, {\it IBVS}, {\bf 4766}

Meinunger, L., 1965, {\it Mitt. Ver\"anderl. Sterne}, {\bf 3}, 109 

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

Richter, G., 1961, {\it Veroeff. Sternw. Sonneberg}, {\bf 4}, 434

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

Spogli C., Fiorucci M., Raimondo G., 2000a, {\it IBVS}, {\bf 4944}

Spogli C., Fiorucci M., Raimondo G., 2000b, {\it IBVS}, {\bf 4977}

\endreferences


\end{document}

