\documentstyle[twoside,tabularx,epsfig]{article}

\input{ibvs2.sty}

\begin{document}

\IBVShead{5250}{4 April 2002}

\IBVStitle{The flare activity of UV Ceti 1982$-$1984}

\IBVSauth{Panov, Kiril P.; Dimitrov, Dinko P.}

\IBVSinsto{Institute of Astronomy, Bulgarian Academy of Sciences,
Tzarigradsko Chosse 72, 1784 Sofia, Bulgaria \\ email: kpanov@astro.bas.bg, dinko@astro.bas.bg}

\SIMBADobj{UV Cet}

\begintext


Photoelectric monitoring observations of the flare star UV Cet have been 
carried out in 1982$-$1984, using the 60$-$cm telescope of the Rozhen 
National Astronomical Observatory and the UBV photon$-$counting, one channel, 
computer controlled photometer. The 1982 observations have been published in 
Panov et al. (1983) and Panov (1984). Here we list the flares observed in 
1983$-$84 (Table~1).  All observing runs were obtained with $1\sec$ integration
in the U band, because of superior flare detection. During the total of 
$10\hr45\mm35\sec$ monitoring, 20 flares were observed. The flare 
characteristics in Table~1 have been described elsewhere (cf. Panov et al., 
2000). The flare energy $E_f$ is obtained as: 

\begin{equation}
\log{E_f}=\log{ED}+\log{E_q}
\end{equation}

where:

\begin{equation}
E_q(U)=2.77\times 10^{27} \mbox{ergs.s}^{-1}
\end{equation}

and

\begin{equation}
E_q(B)=1.73\times 10^{28} \mbox{ergs.s}^{-1}
\end{equation}
~\\
are the quiescent stellar luminosities in the U and B band, respectively. 
These values are obtained with the respective stellar magnitudes and distance, 
taken from Gershberg et al. (1999).

We used the flares from Table~1 to study the flare activity of UV Cet and added
 also flares from other studies in 1982$-$1984, as follows:


4 U$-$band flares from Panov (1984),  8 U$-$flares from Panov et al. (1983),  
2 B$-$band flares from Panov et al. (1983),  3 B$-$flares from Tsvetkov et al. 
(1983),  5 B$-$flares from Ilyin (1984),  1 B$-$flare from Orchiston  et al. 
(1985), and 1 B$-$flare from Mavridis et al. (1990). Unfortunately, not all of 
the flares published are useful for our study, because of insufficient data.


Altogether, 30 U$-$band flares and 12 B$-$band flares were used. The B$-$band 
flare energies were converted to U$-$band energies, using (Lacy et al., 1976):

\begin{equation}
E_U=1.20\times E_B
\end{equation}


For the total sample of 42 flares (total duration=$45\hr 12\mm 27\sec$) we 
calculated the cumulative flare energy distribution:

\begin{equation}
\log \nu=(14.3 \pm 2.5)-(0.49\pm 0.09) \log E_f(U)
\end{equation}
~\\
where $\nu=\frac{N}{T}$ is the cumulative flare frequency and $a$ and $b$ are 
constants  (cf. Gershberg and Shakhovskaya, 1983). Note that flares No.~9 and 
No.~12 are not included in the sample, as we registered only a part of the 
descending light curve. Moreover, in the fit (5) we consider only the linear 
part of the cumulative distribution, corresponding to energies greater than 
$\log E_f(U)=29.4$\ . In our case, this is the threshold of full flare 
detection. In Fig~1, we plotted the total flare sample, together with the 
linear fit from (5). Also shown are the solutions from  Gershberg and 
Shakhovskaya (1983) and Lacy et al. (1976). Our solution for the parameters  
$a$ and $b$ shows significant difference from the two previous solutions in the
sense that during 1982$-$1984 UV Cet possibly was in a state of increased flare
activity.

We would like to thank Dr. K. Olah for her valuable suggestions.

\vspace*{2cm}

\begin{center}
\centerline{Table~1. Characteristics of the U$-$band flares for UV Cet.}
\vskip 5mm
\begin{tabular}{|c|c|c|c|r|c|r|r|c|}
\hline
No. & Date & Flare max & $t_{rise}$ & Duration & Noise    & Amplitude                              & $\Delta m$ & $\log E_f$ \\
       & [UT] & [UT] & [sec] & [m:s] & $\frac{\sigma}{I_0}$ & $\frac{I_{0+f}-I_0}{I_0}$ &  [mag]        & [ergs]         \\
\hline
1.  & 02.10.1983   & 23:44:12   &   11   & $6\mm07\sec$  & 0.41   & 7.83  & 2.36  &  29.69  \\
2.  & 02.10.1983   & 23:55:53   &   88   & $8\mm52\sec$  & 0.23   & 3.93  & 1.73  &  30.23  \\
3.  & 03.10.1983   & 00:05:21   &   62   & $2\mm28\sec$  & 0.58   & 4.35  & 1.82  & 29.67  \\
4.  & 05.10.1983   & 22:58:45   &   5    & $2\mm02\sec$  & 0.73   & 5.86  & 2.09  &  29.52  \\
5.  & 05.10.1983   &$-$&$-$ & $2\mm42\sec$  & 0.49   & $> 1.45$  & $> 1.00$  &$-$ \\ 
6. & 06.10.1983   & 00:15:10   &   38   & $2\mm56\sec$  & 0.52  & 3.78  & 1.70  & 29.49  \\ 
7. & 06.10.1983   & 23:31:48   &   32   & $2\mm22\sec$  & 0.43   & 2.63  & 1.40  & 29.01  \\   
8. & 09.11.1983   &$-$&$-$ & $> 15\mm34\sec$ & 0.15  & $> 3.7$  & $> 1.7$ &$-$ \\   
9. & 10.11.1983   & 21:50:59   &   30   & $7\mm16\sec$ & 0.38   & 4.84  & 1.90  & 29.54  \\   
10. & 10.11.1983   & 22:02:24   &   61  & $2\mm23\sec$  & 0.38   & 1.89  & 1.14  & 29.03  \\   
11. & 04.01.1984   & 17:21:25   &   16   & $1\mm40\sec$  & 0.45   & 4.00  & 1.75  & 29.32  \\   
12. & 04.01.1984   & 17:53:42   &   23   & $1\mm59\sec$  & 0.46   & 3.52  & 1.62 & 29.52  \\   
13. & 04.01.1984   & 18:08:35   &   5    & $24\sec$     & 0.24   & 2.38  & 1.35  & 28.34  \\  
14. & 04.01.1984   & 18:16:02   &   35   & $3\mm07\sec$  & 0.34   & 2.63  & 1.40  & 29.19  \\   
15. & 04.01.1984   & 18:43:41   &   29   & $2\mm06\sec$  & 0.55   & 5.73  & 2.07  & 29.64  \\   
16. & 23.11.1984   & 21:04:55   &   39   & $9\mm04\sec$  & 0.39   & 2.29  & 1.28  & 29.65  \\   
17. & 23.11.1984   & 20:20:56   &   31   & $6\mm49\sec$  & 0.45   & 15.84 & 3.07 & 30.14  \\ 
18. & 23.11.1984   & 20:47:36   &   40   & $1\mm01\sec$  & 0.37   & 3.03  & 1.51  & 29.10  \\   
19. & 24.11.1984   & 20:43:27   &   7    &  $3\mm36\sec$  & 0.63   & 7.67  & 2.34  & 29.67  \\   
20. & 25.11.1984   & 20:49:56   &   44   & $4\mm14\sec$  & 0.65   & 3.98  & 1.74  & 29.58  \\    
\hline 
\end{tabular}
\end{center}

\newpage

\IBVSfig{8cm}{5250-f1.eps}{Cumulative flare energy distribution of our sample 
(full line), Gershberg and Shakhovskaya (1983) (dashed line), and Lacy et al. 
(1976) (dotted line). Crosses are U band flares and diamonds are B band flares.
}


\references

Gershberg R.E., Shakhovskaya N., 1983, {\it ApSS}, {\bf 95}, 235

Gershberg R.E., Katsova M., Lovkaya M., Terebizh A., Shakhovskaya N., 1999, 
{\it A\&AS}, {\bf 139}, 555

Ilyin I.V., 1984, {\it IBVS}, No.~2484

Lacy C.H., Moffett T., Evans D., 1976, {\it ApJS}, {\bf 30}, 85

Mavridis L., Varvoglis P., 1990, {\it IBVS}, No.~3429

Orchiston W., Bembrick C., Park J., Poppleton B., 1985, {\it IBVS}, No.~2785

Panov K.P., Asteriadis G., Mavridis L., 1983, {\it IBVS}, No.~2359

Panov K.P., 1984, {\it BlDok}, {\bf 37}, 557

Panov K.P., Goranova Yu., Genkov V., 2000, {\it IBVS}, No.~4917

Tsvetkov M., Mavridis L., Asteriadis G., 1983, {\it IBVS}, No.~2437

\endreferences

\end{document}
 
