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\IBVShead{4953}{6 September 2000}

\IBVStitletl{UBV Observations of AG D\lowercase{ra}}{ in the End of the Latest Active Phase and After It}

\IBVSauth{Tomov, N.; Tomova, M.}

\IBVSinsto{NAO Rozhen, Institute of Astronomy, P.O. Box 136, BG-4700
Smolyan, Bulgaria,\\ \indent e-mail: rozhen@mbox.digsys.bg}

\SIMBADobj{AG Dra}
\IBVStyp{ symbiotic }
\IBVSkey{photometry}

\IBVSabs{Three colour UBV photometry of the symbiotic binary AG Dra during}
\IBVSabs{its last eruption in 1998 and afterwards was obtained. One brightening}
\IBVSabs{of the star was detected which was followed by a decline to the}
\IBVSabs{quiescent magnitude. The increased U light in the quiescent phase}
\IBVSabs{of the orbital minimum is concluded to be due to mass outflow from the}
\IBVSabs{hot companion during the active phase as well as variations of the}
\IBVSabs{giant's mass-loss rate.}

\begintext

The photometric history of the symbiotic star AG Dra includes many
active phases separated by quiescent periods, which are characterized
with an $U$ colour orbital variability whose amplitude is about one
magnitude.  This variability is supposed to be due to an occultation of
a bright nebular region by the cool giant in the system (Mikolajewska
et al.\ 1995, Friedjung et al.\ 1998). The last active phase was
characterized by five rapid brightenings realized every year from 1994
to 1998 (Petrik \& Hric 1994, Skopal \& Chochol 1994, Montagni et
al.\ 1996, Petrik et al.\ 1998, Tomova \& Tomov 1998). Their amplitudes
were about one magnitude in the $V$ band and reached up to four
magnitudes in the $U$ band. In this note we present new $UBV$ photometric
data acquired during the latest eruption in 1998 and after it, when the
brightness gradually reached its quiescent values.

\begin{table}[h]
\caption{Photometric observations of AG Dra}
\begin{center}
\begin{tabular}{@{}rrccc|rrccc@{}}
\hline
JD${}-{}$2450000&$n$&$V$&$B$&$U$&
JD${}-{}$2450000&$n$&$V$&$B$&$U$\\
\hline
 828.7 & 2 & 9.790 & 11.176 & 11.566 & 1357.3 & 3 & 9.728 & 11.097 & 11.525 \\
 865.7 & 3 & 9.707 & 11.103 & 11.429 & 1401.3 & 3 & 9.702 & 11.094 & 11.460 \\
 866.6 & 3 & 9.713 & 11.089 & 11.433 & 1404.3 & 3 & 9.708 & 11.061 & 11.442 \\
 867.6 & 4 & 9.728 & 11.098 & 11.418 & 1408.3 & 2 & 9.715 & 11.101 & 11.469 \\
 877.6 & 3 & 9.725 & 11.089 & 11.402 & 1437.3 & 3 & 9.766 & 11.150 & 11.422 \\
1007.5 & 2 & 9.659 & 10.828 & 10.195 & 1509.2 & 1 & 9.713 & 11.097 & 11.338 \\
1015.4 & 3 & 9.621 & 10.680 & 10.023 & 1510.2 & 1 & 9.702 & 11.087 & 11.324 \\
1027.3 & 2 & 9.410 & 10.334 & \phantom{1}9.389 & 1581.6 & 3 & 9.758 & 11.120 & 11.112 \\
1087.2 & 2 & 9.643 & 10.764 & 10.181 & 1626.5 & 4 & 9.753 & 11.088 & 11.026 \\
1088.2 & 2 & 9.628 & 10.777 & 10.222 & 1627.5 & 4 & 9.740 & 11.090 & 11.011 \\
1226.6 & 3 & 9.747 & 11.148 & 11.402 & 1715.4 & 3 & 9.822 & 11.222 & 11.320 \\
1239.6 & 3 & 9.754 & 11.135 & 11.407 & 1716.5 & 2 & 9.833 & 11.235 & 11.343 \\
1293.4 & 3 & 9.818 & 11.219 & 11.513 & 1718.5 & 2 & 9.823 & 11.220 & 11.362 \\
1298.4 & 4 & 9.797 & 11.217 & 11.518 & 1721.4 & 3 & 9.827 & 11.240 & 11.379 \\
1332.4 & 3 & 9.794 & 11.190 & 11.527 & & & & & \\
\hline
\end{tabular}
\end{center}
\end{table}

Three colour $UBV$ photometry of AG Dra was obtained during January
1998--June 2000 (Table~1) with a single channel photoelectric
photometer, mounted at the Cassegrain focus of the 0.6-m telescope of
the National Astronomical Observatory Rozhen. The comparison stars and
the accuracy of the measurements were the same like those presented in
the work of Tomova \& Tomov (1998). To consider our quiescent data we
used the ephemeris ${\rm JD}(U_{\rm min})=2\,442\,514.4+552.4\times E$
of Skopal and Chochol (1994). The zero epoch is that of the photometric
minimum, when the cool giant is in front of the hot component.

\IBVSfig{12cm}{4953-f1.eps}{The $UBV$ light curves of AG Dra}

Figure~1 gives the three-colour light curve of AG Dra during the time
of the observations. It is seen that the brightening of the star in
1998 is followed by a period of quiescence when the light in the $B$
and $V$ spectral regions reached its typical values during quiescent
state. At that time the variations of the $U$ light were probably
determined by the orbital motion, since the smallest and greatest
values are at the epochs of the orbital photometric minimum and
maximum. Our data are not complete during the eruption, but they show
that the light varied in all the colours and the amplitude of the
variation was larger for the shorter wavelengths. The variation of the
$U$ magnitude indicates an increase by a factor of 4.8 of the light
compared with the quiescent period before the 1994--1998 active phase.
The $B$ and $V$ increase factors are 2.0 and 1.3.

The brightness at the time of the orbital minimum is greater than the
brightness at the orbital minima during the quiescent stage before 1994
(Hric et al.\ 1993, Hric et al.\ 1994). Its increased value is
determined by the greater number of the recombinating ions in the
circumbinary nebula. Tomov et al.\ (2000) considered the $U$ orbital
variations of AG Dra during quiescence.  They came to the conclusion
that the whole circumbinary nebula of this system is an ionized region
(except the portion occulted by the cool star) as its hot stellar
component is very luminous.  Consequently, the growth of the luminosity
alone will not lead to an increase of the number of the recombinating
ions. It can be caused by a growth of the mass-loss rate of the giant
star (Friedjung et al.\ 1998), and because of a mass outflow by the hot
component during the active phase as well.  On the other hand, there are
no pronounced minima on the $B$ and $V$ light curves at the epoch of this
orbital minimum, which is due to the different pattern of variability
of the light of AG Dra in the region of these photometric systems
(Bastian 1998, Friedjung et al.\ 1998).

The authors thank their colleague Dr.\ R.~Zamanov for his helpful modification 
of the processing software.

\references

Bastian, U., 1998, {\it A\&A}, {\bf 329}, L61

Friedjung, M., Hric, L., Petrik, K., Galis, R., 1998, {\it A\&A},
{\bf 335}, 545

Hric, L., Skopal, A., Urban, Z., Kom\v{z}\'{i}k, R., Luthardt, R.,
Papou\v{s}ek, J., Han\v{z}l, D., Blanco, C., Niarchos, P., Veli\v{c},
Z., Schweitzer, E., 1993, {\it Contr.\ Astr.\ Obs.\ Skalnat\'{e} Pleso},
{\bf 23}, 73

Hric, L., Skopal, A., Chochol, D., Kom\v{z}\'{i}k, R., Urban, Z., 
Papou\v{s}ek, J., Blanco, C., Niarchos, P., Rovitis-Livaniou H.,
Rovitis, P., Chinarova, L.L., Pikhun, A.I., Tsvetkova, K., Semkov, E.,
Veli\v{c}, Z., Schweitzer, E., 1994, {\it Contr.\ Astr.\ Obs.\ Skalnat\'{e} 
Pleso}, {\bf 24}, 31

Mikolajewska, J., Kenyon, S.J., Mikolajewski, M., Garcia, M.R., Polidan, R.S.,
1995, {\it AJ}, {\bf 109}, 1289
	
Montagni, F., Maesano, M., Viotti, R., Altamore, A., Tomova, M.,
Tomov, N., 1996, {\it IBVS}, No.~4336

Petrik, K., Hric. L., 1994, {\it IAU Circ.}, No. 6073

Petrik, K., Hric. L., Galis, R., Friedjung, M., Dobrotka, A., 1998, 
{\it IBVS}, No.~4588

Skopal, A., \& Chochol D., 1994, {\it IBVS}, No.~4080

Tomova, M., Tomov, N., 1998, {\it IBVS}, No.~4561

Tomov, N., Tomova, M., Ivanova, A., 2000, {\it A\&A}, submitted


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