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\IBVShead{4408}{10 December 1996}

\title{RY TAURI AT HIGH BRIGHTNESS}

\begintext

    The T Tau star RY Tau has increased its brightness from V=10\fm 6 to V=9\fm 6 
in the period from middle of October to middle of November this year, with 
no changes in U$-$B and B$-$V. Photometric monitoring of RY Tau is going on
at the Crimean Laboratory of the Sternberg Astronomical Institute, Russia,
with the 60-cm telescope and the photon-counting photometer. The following is 
a subset of the photometric data from 1995 and the recent observations in 
October and November 1996 (also plotted in Figure 1):
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\begin{tabular}{crcc}
\hline
JD 2450... &   V  &    U$-$B&     B$-$V \\
\hline
060.3042 &   10.57 &  +0.56 &  +1.09\\
064.4076 &   10.46 &   0.56 &   1.08\\
 ...     &  ...    & ...    & ... \\
362.5437 &   10.60  &  0.38 &   0.96\\
373.5500 &   10.22  &  0.51 &   1.04\\
392.5924 &   10.01  &  0.59 &   1.09\\
400.4896 &    9.85  &  0.58 &   1.05\\
402.5382 &    9.60  &  0.46 &   1.01\\
408.4861 &    9.72  &  0.60 &   1.07\\
\hline
\end{tabular}
\end{center}
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\centerline{Figure 1. Light and colour variations of RY Tau}
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Figure 2. Variations in H$\alpha$ profile: the most intensive profile
is of December 1995 (low brightness of the star), others are of November 1996
(high brightness)
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Figure 3. Fragment of the photospheric absorption spectrum of RY Tau,
taken at different brightness of the star (the spectra are overplotted). 
No difference in line profile or intensity is noticeable
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\centerline{3}
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    High-resolution echelle spectra of RY Tau were taken with the SOFIN 
spectrograph at the 2.5-m Nordic Optical Telescope (La Palma, Spain), 
at low brightness of the star (5 Dec. 1995) and at high brightness (20 Nov., 
22 Nov., 25 Nov., 27-30 Nov. and 1 Dec. 96). The spectral range was 400-900 nm, the resolving power 25000, S/N ratio 170. In spite of the large 
brightness difference, all the spectra show the same photospheric spectrum 
of a late G star, with the same line depths and line ratios, and with the 
same veiling factor of about 0.5. The equivalent width of H$\alpha$ emission 
has changed from 1.8 nm to 0.7 nm, that is the flux radiated in the line 
remains at about the same level as before the brightening of the star (see Figure 2). 
The spectra taken at high brightness of RY Tau show the usual night-to-night 
variations in emission line profiles of HI and CaII: superposition of broad 
emission with multiple variable absorption components at radial velocities 
from +50 to $-$150 km/s. No variations were found in photospheric absorption 
lines (see Figure 3).

    Similar event of brightening of RY Tau by more than one magnitude with
constant colours was observed in 1983/84 (Zajtseva et al., Sov. Astron.Lett.,
11(2), 109, 1985). 
  
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\beginauthors
\authorsrightcol
G. ZAJTSEVA
Sternberg Astronomical Institution, 
Russia
\vskip 2mm
P. PETROV
Crimean Astrophysical Observatory,
Ukraine
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I. ILYIN
R. DUEMLER
I. TUOMINEN
University of Oulu, Finland
\endauthors

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