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\IBVShead{4901}{8 May 2000}

\IBVStitletl{New Photoelectric Minima and Light Elements of}{ MM Herculis }

\IBVSauth{Ta\c{s}, G.}

\IBVSinsto{Ege University Observatory, 35100 Bornova, \.{I}zmir, Turkey, e-mail: tas@alpha.sci.ege.edu.tr}

\SIMBADobjAlias{MM Her}{HD 341475}
\IBVStyp{ RS CVn - type binary star }
\IBVSkey{eclipsing binaries}

\IBVSabs{In this study, the times of minima obtained from 1998-1999}
\IBVSabs{photometric observations of MM Herculis are presented and}
\IBVSabs{the new light elements are given. The variation of $O-C$ residuals can either}
\IBVSabs{be the result of a light-time effect or magnetic activity.}

\begintext

The variability of the RS CVn type eclipsing binary MM Herculis
(BD\,+22\deg 3245, HD 341475) was discovered by Tsesevich (1954).
Previous observational data were well studied up to now by several
authors. The last period analysis of MM Her was made by Evren (1985)
and the light elements of the system were computed.

The observations in Johnson's $B$, $V$, $R$ filters were made at the Ege
University Observatory in 1998 and 1999. The new light curves obtained
from these observations have been published by Ta\c{s} (2000). The
times of four primary minima obtained in this study are listed in Table
1.

The $O-C$ (I) residuals in Table 1 were computed from the light elements
given by Evren (1985) as
$$
{\rm HJD_{min\,I}} = 2445551.4336 + 7\fday960358 \times E.
$$

The least squares solution has been computed from all photoelectric
minima given by Hall and Kreiner (1980), Evren (1985) and this study,
and the new light elements were derived as follows:
$$ \begin{array}{r@{}r@{}l}
{\rm HJD_{min\,I}} = 2445551.4274 & {} + 7\fday960326 & {} \times E. \\
{} \pm 7 & {} \pm 2 \\
\end{array} $$

The $O-C$ (II) residuals were computed using these new light elements
and all of them have negative sign. These residuals were plotted
against cycle values ($E$) and are shown in Figure~1.

As seen from Figure 1, the $O-C$ (II) residuals may be represented with
a sine-like variation. Our values (filled circles in Figure 1) are seen
on the descending branch of this variation. This variation can either
be the result of a light-time effect or magnetic activity. Our studies
concerning the third body orbit and the physical parameters of the
third companion being continued and will be discussed elsewhere.



\begin{table}
\caption{Times of new primary minima for MM Her}
\begin{center}
\begin{tabular}{ccccc}
\hline
JD (Hel.) & \lower6pt\hbox{$E$} & $O-C$ (I) & $O-C$ (II) & \lower6pt\hbox{Filter} \\[-3pt]
(24 00000+) & & (day) & (day) & \\
\hline
50956.48586 & 679 & $-$0.03082 & $-$0.00288 & $V$ \\ 
50956.48592 & 679 & $-$0.03076 & $-$0.00282 & $B$ \\ 
50956.48615 & 679 & $-$0.0305 & $-$0.0026 & $R$ \\ 
50964.44694 & 680 & $-$0.0301 & $-$0.0021 & $R$ \\ 
50964.44701 & 680 & $-$0.0300 & $-$0.0021 & $V$ \\ 
50964.44801 & 680 & $-$0.0290 & $-$0.0011 & $B$ \\ 
51362.45861 & 730 & $-$0.0363 & $-$0.0067 & $V$ \\ 
51362.45949 & 730 & $-$0.0354 & $-$0.0059 & $R$ \\ 
51362.46187 & 730 & $-$0.0331 & $-$0.0035 & $B$ \\ 
51378.38174 & 732 & $-$0.0339 & $-$0.0043 & $R$ \\ 
51378.38212 & 732 & $-$0.0335 & $-$0.0039 & $B$ \\ 
51378.38272 & 732 & $-$0.0329 & $-$0.0033 & $V$ \\ 
\hline
\end{tabular}
\end{center}
\end{table}

\IBVSfig{8.9cm}{4901-f1.ps}{The $O-C$ (II) variation of MM Her. The symbols of plus and
filled circle represent the data taken from literature and this study, respectively.}

{\it Acknowledgements:} I would like to thank Drs.~C.~Ibanoglu and
S.~Evren for their guidance. This work was supported by Ege
University Research Fund (Project No.\ 99 FEN 014).

\references

Evren, S., 1985, {\it Astrophys.\ Space Sci.}, {\bf 108}, 113

Hall, D.S. and Kreiner, J.M., 1980, {\it Acta Astron.}, {\bf 30}, 387

Ta\c{s}, G., 2000, {\it IBVS}, No.\ 4883.

Tsesevich, V.P., 1954, {\it Odessa Izv.}, {\bf 4}, Part 2, 116

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