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\IBVShead{4390}{4 November 1996}

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{\ft PHOTOMETRIC AND POLARIMETRIC OBSERVATIONS \smallskip \\ OF SEVEN MIRAS}
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Photometric and polarimetric observations of red giants and supergiants have been carried out at 
the Byurakan Astrophysical Observatory since 1957. In 1994, Magnan suggested to include in that 
program systematic photometric observations of Mira Ceti type long period variables. Preliminary 
results of those observations are given in this paper.

Seven  long period  Mira-type variables were observed in Byurakan Observatory during 
April-September 1996. The observations have been made with the photopolarimeter attached to the 
AZT-14 50cm-telescope. That photopolarimeter works in the regime of intensification of the 
direct current. It can be used either as a photoelectric photometer (without the polaroid) or as 
a photopolarimeter (with the polaroid). The maximum of sensitivity of the photomultiplier lies 
in the wavelength interval 4000--4400~{\AA}. The observations have been done in the U, B, V, R 
bands, sometimes without the filter (``filter~0''). A more detailed description of the method 
and instruments has already been given elsewhere (Eritsian and Nersisian, 1984).

The results of polarimetric observations for the Mira variables are presented in Table~1. The 
columns of the table successively give (i) the name of the star from the General Catalogue of 
Variables Stars (GCVS), (ii) the date of the observation, (iii) the observed degree of 
polarization $P$ in the U, B, V, R bands (when the observations have been done without any 
filter, this is indicated by the term ``filter~0'') and (iv) the angle of polarization  
$\theta$. The uncertainties in the photometric and polarimetric measurements respectively are 
$\sigma_{UBV}$ = 0\fm 02 - 0\fm 04, 
$\sigma_P({UBV})$ = 0.1 - 0.2\%. The uncertainty in the determination of the 
polarization angle is $\sigma_{\theta} = 1\degr - 3\degr$.

As can be seen from Table~1, a light polarization has been detected for the stars R~Aql, RT~Cyg 
and S~UMi. In those three cases, the variable character of the polarization has been confirmed.

As a noteworthy result, a rapid light variation of the star T~Cep has been found
about two months after the maximum of brightness. The corresponding data in the B and V bands 
are given in Table~2. The light variations  are drawn in Figure 1. The solid straight line 
represents the mean light-curve in V-color, which has been obtained from the data of the GCVS 
(1985) by knowing the epoch of maximum and the phase. One can see that the whole event lasted 
less than 20 days but the duration of the peak itself represents only a few days.


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\centerline{Table 1. Polarimetric observations of 7 Mira Ceti type stars}
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\begin{tabular}{|cc|cccc|cccc|}
\hline
 star & date & \multicolumn{4}{c|}{$P$(\%)}&\multicolumn{4}{c|}{$\theta(^\circ)$}
\\
\cline{3-10}
(GCVS)& (UT)  &\multicolumn{1}{|c}U&B&V&\multicolumn{1}{c|}R&U&B&V&\multicolumn{1}{c|}R\\
\hline
R Aql& 14.07.96&\multicolumn{3}{c}{filter 0}&2.2&
 \multicolumn{4}{c|}{130}\\
&08.08.96&--&--&--&$\leq 0.3$&--&--&--&--\\
&09.09.96&--&--&$\leq 0.3$& 0.6& --&--&--&31\\
&15.09.96&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&1.0&--&--&--&35\\
&&&&&&&&&\\
T Cep & 20.05.96&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&--&--&--&--\\
&21.05.96&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&--&--&--&--\\
&22.05.96&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&--&--&--&--\\
&09.06.96&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&--&--&--&--\\
&10.09.96&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&--&--&--&--\\
&&&&&&&&&\\
RT Cyg&15.07.96&--&1.5&1.2&0.9&--&65&35&40\\
&16.07.96&5.0&1.5&1.3&1.2&45&35&45&60\\
&10.09.96&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&--&--&--&--\\
&15.09.96&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&--&--&--&--\\
&&&&&&&&&\\
R Dra&14.07.96&--&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&--&--&--&--\\
&15.09.96&--&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&--&--&--&--\\
&&&&&&&&&\\
X Oph&09.06.96&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&--&--&--&--\\
&13.07.96&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&--&--&--&--\\
&16.07.96&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&--&--&--&--\\
&09.09.96&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&$\leq 0.3$&--&--&--&--\\
&&&&&&&&&\\
S UMi&15.07.96&--&$\leq 0.5$&$\leq 0.5$& 0.9&--&--&--&45\\
&15.09.96&$\leq 0.5$&$\leq 0.5$&$\leq 0.5$&$\leq 0.5$&--&--&--&--\\
&&&&&&&&&\\
R Vir&22.04.96&$\leq 0.5$&$\leq 0.5$&$\leq 0.5$&$\leq 0.5$&--&--&--&--\\
&&&&&&&&&\\
\hline
\end{tabular}
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\centerline{Table 2. Rapid variation of T~Cep}
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\begin{tabular}{|c|c|c|}
\hline
Date   &    B    &   V  \\
\hline
20 May 1996 & 8.72 & 7.06\\
21 May 1996 & 8.12 & 6.67\\
22 May 1996 & 8.56 & 6.91\\
09 June 1996 & 9.11 & 7.80\\
\hline
\end{tabular}
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\centerline{Figure 1. Rapid variation of T Cep}

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{\noindent Acknowledgements:}
 One of the authors (Melikian) is very grateful to Drs. Christian Magnan and Marie-Odile 
Mennessier for their hospitality and the possibility they gave him to work in the Montpellier 
University. He duly acknowledges the support of the direction of the PICS~247, which coordinates 
the French--Armenian collaboration in astronomy at the national level. He is also much indebted 
to the University of Montpellier for its financial support in the framework of the exchanges 
with the University of Erevan.

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\beginauthors
\authorsrightcol
C. MAGNAN, 
M.-O. MENNESSIER
GRAAL, Universit\'e de Montpellier~II, 
France
e-mail: magnan@graal.univ-montp2.fr
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N.D. MELIKIAN 
M.H. ERITSIAN, 
A.A. KARAPETIAN
Byurakan Astrophysical Observatory, 
Armenia
e-mail: byurakan@pnas.sci.am
\endauthors


%\references
Reference:

Eritsian, M.A.,  Nersisian, S.E., 1984, {\it Astrofizika}, {\bf 20}, 355

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\centerline{\bf ERRATUM}

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In IBVS No.\,4359 issue, Table 1 contains incorrect data on the minima of V676 Cen. 
The revised table is as follows:
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\begin{tabular}{cccrc}
\hline
JD Hel&Eclipse Type&Cycles&(O$-$C)$_1$&(O$-$C)$_2$\\
2400000+& & & & \\
\hline
48393.5174(1)&I&4863.0&$-$0.0001&0.0001\\
48394.6872(1)&I&4867.0&0.0001&0.0002\\
\hline
\end{tabular}
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\hfill J.D. GRAY

\hfill S. WOISSOL

\hfill R.G. SAMEC

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