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\IBVShead{4523}{3 October 1997}

\IBVStitletl{Photometric and polarimetric observations}{ of the post-AGB star SAO~124414}

\IBVSauth{N.D.~MELIKIAN$^1$, M.A.~ERITSIAN$^1$, A.A.~KARAPETIAN$^1$, A.~LEBRE$^2$}

\IBVSinst{Byurakan Astrophysical Observatory, Armenia, e-mail: nmelikia@helios.sci.am}
\IBVSinst{GRAAL cc072, Universit\'e Montpellier II, 34095 Montpellier, France, 
e-mail: lebre@graal.univ-montp2.fr}

\SIMBADobj{SAO 124414}

\begintext

\vspace{-12mm}

Post-AGB stars are suspected to be in an intermediate evolutionary 
state between asymptotic giant branch and planetary nebula stages. 
Together with the study of long period variables (Mira Ceti type stars) we 
have performed a photometric and polarimetric monitoring of 4 post-AGB stars, 
from March to July 1997. 
In this paper, we present the preliminary results of these observations 
for one of these objects: SAO~124414.

The observations have been carried out with the photopolarimeter 
attached to the 50cm AZT-14 telescope of Byurakan observatory. Detailed 
description of the observational method and instruments has already been 
published (Eritsian, Nersisian, 1984 and Magnan et al., 1996). 
The observations have been done in B, V, R bands. 
The uncertainties in the photometric and 
polarimetric measurements are $\sigma$=0.01--0.02 mag and 
$\sigma_P$=0.1--0.2\%, respectively. The uncertainty in the 
determination of the polarization angle is $\sigma$($\theta$)=1--2\deg.

During the observational period, no significant light variation was 
detected. In Table 1 we present the results 
of photometric and polarimetric observations for the star SAO~124414. 
We display the Heliocentric Julian 
dates of observations (column 1), the  B, V and R magnitudes (columns 2 to 4), 
the degree of polarization in B, V and R bands (columns 5 to 7) and the 
polarization angle (columns 8 to 10).




\begin{table}
\caption{
Photometric and polarimetric measurements for SAO~124414}
\begin{center}
\begin{tabular}{cccccccccc}
\hline
Julian date   &  B  &  V & R   &  P\%(B)  &  P\%(V)  &  P\%(R)   &  $\theta$(B)  &  
$\theta$(V) 
& $\theta$(R)\\
\hline
2450603.33 & 9.58 & 8.61 & 8.42 &  3.0  &   2.0  &  1.8 & 124\deg & 132\deg &  127\deg\\
2450603.39 & 9.58 & 8.61  &8.42  & 3.0   &  2.0  &  1.8 & 124  &    132 & 127\\
2450604.27 & 9.58 & 8.60  &8.41  & 3.0  &   2.0 &   1.7 & 125  &    130 &  127\\
2450613.23 & 9.62 & 8.61 & 8.40 &  3.5  &   2.0  &  2.0 & 129  &    129 & 126\\
2450613.27 & 9.61 & 8.61 & 8.40  & 3.5  &   2.0  &  2.0 & 129  &    129 &  126\\
2450613.32 & 9.60 & 8.59 & 8.42  & 3.5  &   2.0  &  2.0 & 128  &    127 &  126\\
2450613.36 & 9.60 & 8.60 & 8.41  & 3.5  &   2.0  &  2.0 & 129  &    128 &  126\\
2450613.42 & 9.62 & 8.61 & 8.40  & 3.5  &   2.0  &  2.0 & 129  &    128 &  127\\
2450637.29 & 9.59 & 8.60 & 8.40  & 2.7  &   2.1  &  1.6 & 138  &    129 &  128\\
2450638.31 & 9.59 & 8.61 & 8.41  & 2.8  &   2.2  &  1.5 & 124  &    148 &  138\\
2450640.30 & 9.60 & 8.62 & 8.40  & 2.1  &   1.6  &  0.8 & 140  &    135 &  135\\
2450640.38 & 9.61 & 8.60 & 8.40  & 2.1  &   1.6  &  0.8 & 139  &    135 &  133\\
2450640.50 & 9.60 & 8.61 & 8.40  & 2.2  &   1.6  &  0.8 & 140  &    135 &  135\\
2450641.25 & 9.58 & 8.59 & 8.42  & 3.7  &   3.1  &  1.3 & 143  &    138 &  129\\
2450641.39 & 9.58 & 8.59 & 8.40  & 3.7  &   3.1  &  1.3 & 142  &    137 &  126\\
2450641.47 & 9.58 & 8.60&  8.40  & 3.7 &    3.1 &   1.3 & 142  &    137 &  127\\
\hline
\end{tabular}
\end{center}
\end{table}

As one can see from the data listed in Table~1, while the 
brightness of the star is constant during the observational period, a 
significant time variation of polarization is 
detected. The absence of polarization of nearby background stars that 
we have also observed, the time variation and the wavelength dependence 
of linear polarization of SAO~124414 
indicate that this detected polarization has an intrinsic character, 
as already mentioned in Trammell et al.\ (1994). This confirms that the 
star SAO~124414 has an extended circumstellar envelope (see for instance 
Hawkins et al, 1995). The varying polarized light that we have detected 
for SAO~124414 may be the result of inhomogeneities and/or unstable 
morphology of the nebula.

\pagebreak

\references

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

Hawkins, G.W., Skinner C.J., Meixner M.M., Jernigan J.G., Arens J.F., 
Keto E., Graham J.R. 1995, {\it Astrophys.\ J.}, {\bf 452}, 314

Magnan, C., Mennessier, M.O., Melikian, N.D., Eritsian, M.H., Karapetian, A.A., 
1996, {\it IBVS},\ No. 4390

Trammell, S.R., Dinerstein, H.L., Goodrich R.W., 1994, {\it Astron.\ J.}, 
{\bf 108}, 984 

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