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\centerline{\ft PHOTOMETRIC OBSERVATION OF T TAURI TYPE STARS:}
\centerline{\ft DI Cep, T Tau, V410 Tau, GW Ori, V649 Ori}
\vskip 8mm

\begintext

Most of the pre-main sequence stars, as well as T Tauri type
stars, are characterized by some kind of variability of their brightness.
In the $UBV$ photometric system, magnitudes of these stars change by up to
2.8 mag on a time scale of hours to years (e.g. Appenzeller and Mundt,
1989; Herbst et al., 1994).

Photometric observations over the past 50 years showed that sometimes
regular, sometimes erratic behaviour casts some light on the processes
taking place in these objects and on their interaction with the
environment. On the analysis of more than 10000 entries on 80 young stars,
Herbst et al. (1994)  proposed that there were three groups of light
variations related to the spectra of these stars. Application of modern
Fourier analysis methods now allows to reveal periodic components of
light variability for some of these objects. This property of the T
Tauri stars can be explained by rotational modulation for a star with
an asymmetric distribution of spots on its surface (e.g. Vrba et al.,
1989; Shevchenko et al., 1991). However, a more detailed study of these
objects needs a large quantity of observational data on individual
stars during a long time interval.

Our $WBVR$ observations of the T Tauri type stars DI Cep, T Tau, V410 Tau,
GW Ori, and V649 Ori were carried out in autumn 1995 with the single-channel
photon-counting photometer attached to the 60 cm telescope at the
Crimean laboratory of Sternberg Astronomical Institute (Moscow).
Observations were done by differential photometry. All stars were
measured together with two comparison stars, and background light was
measured at least twice in each  band.  For transformation to the
standard system, we observed standard stars of luminosity classes IV--V
and late spectral types from the list of Kornilov et al. (1991). Rms
errors of the differential photometry are about 0.01--0.02 mag for
$BVR$ bands and 0.03 mag for the $W$ band.  In this note, we report on
the results of observations for five objects.  The results are
presented in the table.

Application of the $W$ photometric band (Straizys, 1977) for CTTSs has
some advantages compared to the $U$ band; thus, the $W$ band has lower
transmission at larger wavelengths decreasing the influence of the
Balmer jump, which is essential for stars with emission-line spectra.
On the other hand, the $W$ band reduces the red leak, while the $U$
band has a considerable red leak. Our measurements in the $W$ band
showed little difference compared to
$U$ band measurements of other authors (see, e.g., Herbst et al., 1994).
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\centerline{2}
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\begin{center}
Table 1. $WBVR$ observations of T Tauri stars
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\medskip
\normalsize
\begin{tabular}{lrrrrlrrrr}
\hline
\noalign{\medskip}
JD24...&$V$&$W-B$&$B-V$&$V-R$&JD24...&$V$&$W-B$&$B-V$&$V-R$\\
\noalign{\medskip}
\hline
\noalign{\medskip}
{\bf T Tau}& & & & &{\bf GW Ori}\\[5pt]
  50002.223&9.91&0.59&1.28&0.75&    50002.320&9.67&0.38&1.03&0.90\\
  50003.423&9.90&0.47&1.20&0.76&    50003.377&9.69&0.38&1.02&0.88\\
  50004.420&9.96&0.57&1.16&0.78&    50004.390&9.73&0.37&1.03&0.89\\
  50004.502&9.89&0.55&1.19&0.70&    50004.552&9.81&0.34&0.96&0.92\\
  50005.402&9.91&0.58&1.19&0.73&    50006.467&9.80&0.46&0.88&0.95\\
  50006.355&9.92&0.57&1.10&0.80&    50006.550&9.97&0.38&0.86\\
  50006.379&9.94&0.50&1.18&0.80&    50007.464&9.93&0.38&0.89\\
  50006.466&9.93&0.58&1.22&0.71&    50008.462&9.88&0.37&0.88\\
  50007.353&9.96&0.56&1.26 & &      50009.434&9.82&0.36&0.91&0.90\\
  50007.420&9.97&0.55&1.23 & &      50010.397&9.75&0.38&0.94&0.94\\
  50008.387&9.86&0.54&1.16\\
  50009.361&9.90&0.52&1.17&0.79\\
  50010.363&9.91&0.53&1.19&0.73\\[5pt]
{\bf DI Cep} \\[5pt]
  49970.420&11.43&--0.15&0.87&0.57&  50006.195&11.46& 0.06&0.91&0.57\\
  49973.401&11.40&--0.13&0.90&0.56&  50006.233&11.46& 0.06&0.94&0.68\\
  49974.422&11.38&--0.17&0.91&0.58&  50007.198&11.36&--0.26&0.89\\
  50002.402&11.68&--0.12&0.62&0.88&  50008.197&11.40&--0.24&0.88\\
  50003.208&11.71&--0.25&0.65&0.89&  50008.242&11.38&--0.25&0.90\\
  50004.202&11.41&--0.18&0.92&0.60&  50009.218&11.36&--0.18&0.87&0.59\\
  50004.289&11.43&--0.12&0.96&0.59&  50009.270&11.36&--0.07&0.80&0.60\\
  50005.206&11.42&--0.21&0.73&0.59&  50010.309&11.36&--0.15&0.91&0.55\\
  50005.261&11.43& 0.04&0.75&0.55&   50010.367&11.35&--0.14&0.91&0.55\\
  50006.177&11.14&--0.32&0.21&0.26\\[5pt]
{\bf V410 Tau} & & & & & {\bf V649 Ori} \\[5pt]
  49969.576&10.77&0.89&1.27&0.93&   50002.379&12.02&0.51&1.11&0.72\\
  49972.533&11.03&0.84&1.01&1.23&   50003.472&12.00&0.49&1.10&0.74\\
  49974.451&10.86&0.82&1.16&0.98&   50004.420&11.99&0.53&0.98&0.77\\
  50002.125&10.86&0.75&1.15&0.97&   50007.473&11.98&0.57&1.01\\
  50003.323&10.98&0.91&1.02&1.20&   50008.484&12.09&0.59&0.91\\
  50004.310&10.75&0.86&1.28&0.97&   50009.442&12.11&0.51&0.99&0.82\\
  50005.420&10.85&0.83&1.17&0.96&   50010.413&12.12&0.46&1.06&0.85\\
  50006.299&10.97&0.95&1.07&1.18\\
  50007.320&11.06&0.89&0.95\\
  50008.346&10.87&1.03&1.16\\
\noalign{\medskip}
\hline
\end{tabular}
\end{center}
\large
\vskip 5mm
Fortunately, a long sequence of clear nights on October 10--20 allowed me
to get continuous measurements of some program stars. In the table, we presented
Julian Dates, $W$, $B$, $V$, and $R$ measurements.

  Photometric monitoring of T Tauri type stars by different authors
  has revealed periodic variations in some stars, with periods
 between 2 and 15 days. Our data allow us to monitor
 variability of the program stars continuously, for 7--10 days. Moreover,
 our measurements show light variability of some stars within a night.

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\centerline{3}
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\epsfysize=9.5cm
\centerline{\epsffile{4470-f1.ps}}
\centerline{Figure 1}

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\centerline{\epsffile{4470-f2.ps}}
\centerline{Figure 2}
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  In Figures 1 and  2, as an example, we present portions of light curves
  respectively of DI Cep and T Tau in all photometric bands. Figure 1 shows
 that, on JD 2450006, DI Cep increased its brightness by 0\fm 2
 in $W$ and $B$ and by 0\fm 1 in $V$ and $R$ bands. Thus, we see photometric
 activity of DI Cep during that night. Other program stars showed no
 marked photometric activity ($\Delta$V$\le$0\fm 1).
\vfill \eject

\centerline{4}
\vskip 1mm

 So, continuous photometric monitoring has not revealed evident
 periodic modulation of brightness for program stars.
 We observed variability in $WBVR$ bands within $\Delta$V=0\fm 1
 for all stars and a higher photometric activity for DI Cep.


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\beginauthors
\authorsrightcol
N.Z. ISMAILOV
Sternberg Astronomical Institute
13, Universitetskij Prosp.,
Moscow 119899, Russia
\endauthors

\references

Appenzeller, I., Mundt, R., 1989, {\it Astron.Astrophys.Rev.}, {\bf 1}, 291

Herbst, W., Herbst, D.K., Grossman, E.J., Weinstein  D., 1994, {\it Astron. J.}, {\bf 108},
1906

Kornilov, V.G., Volkov, M.I., Zakharov, A.I. et al., 1991, Trudi GAISH, LXIII

Shevchenko, V.S., Grankin, K.N., Ibragimov, M.A. et al., 1991, {\it IBVS}, No.\,3652

Straizys, V., 1977, Multicolor Stellar Photometry, ``Mokslas", Vilnius

Vrba, F.J., Rydgren, A.E., Chugainov, P.F. et al., {\it 1989}, {\it Astron. J.}, {\bf 97}, 483

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