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\IBVShead{5293}{17 June 2002}

\IBVStitletl{A possible periodic term in the period}{ of the eclipsing binary V701 S\lowercase{co}}

\IBVSauth{Mayer, Pavel; Wolf, Marek}

\IBVSinsto{Astronomical Institute, Charles University Prague, 
           V~Hole\v sovi\v ck\'ach 2, 180 00 Praha 8, Czech Republic,\\
           e-mail: mayer@mbox.cesnet.cz}

\SIMBADobj{V701 Sco}
\IBVStyp{eclipsing binaries}
\IBVSkey{photometry; times of minima; orbital period changes}

\IBVSabs{Times of minima are used}
\IBVSabs{to suggest a periodic term in the length of the orbital period}


\begintext

The early-type (B1) eclipsing binary V701~Scorpii (also HD~317~844, HIP~85985, 
\hbox{CD~$-$32~12924}), due to its membership in the open cluster NGC~6383, was 
studied several times: spectroscopically by Andersen et al. (1980) and 
photometrically e.g. by Bell \& Malcolm (1987). Its period is apparently 
variable, as found already by Andersen et al. (1980).
These authors invoked large mass transfer to explain the variability;
however, Bell \& Malcolm (1987) did not confirm any large period change and
noted that there is some evidence of small-scale period changes only.

One of us (MW) recently measured a part of a minimum using the 0.84-m 
telescope at San Pedro M\'artir Observatory (Baja California, Mexico). 
Only the rising part of the minimum was catched, nevertheless the time 
of the minimum can be estimated when the data are compared with measurements 
by Bell \& Malcolm (1987) or Lorenz et al. (1991). In Table 1, all available 
times of minimum light are collected; in agreement with previous 
studies, the minimum time published by Bruton \& Chambliss (1985) is not
considered. In the column $O-C_1$ the values calculated using the ephemeris
by Bell \& Malcolm are given:

\medskip
Pri.Min. = HJD $2446199.5059 + 0\fday76187645 \cdot E,$ 
\medskip

\noindent and in the column $O-C_2$ are values according to a somewhat 
arbitrary ephemeris

\medskip
Pri.Min. = HJD $2446199.4850 + 0\fday7618728 \cdot E. $
\medskip

\noindent The $O-C_2$ values are displayed in Fig. 1. It can be observed 
that there might be a periodic term in $O-C$ values, and a sine curve is
also shown. Its semiamplitude is $0\fday028$, period 67 years, phase zero
at JD 2442390; these values are however constrained only weakly. In case
the periodic change is due to a third body, the mass function is 
0.0256~M$_{\odot}$ and the minimum third body mass is 2.2 M$_{\odot}$ (a
better fit would be obtained assuming nonzero eccentricity of the third 
body orbit). If the periodic behaviour is confirmed, no assumption of
mass exchange is necessary.


\newpage

{\small
\begin{table}
\begin{center}
\caption{Times of minima of V701~Sco}
\bigskip
\begin{tabular}{clrccc}
\hline
HJD$-2400000$ & Error  & Epoch$\;\;$ & $O-C_1$ & $O-C_2$ & Source \\
              & [days] &             & [days]  & [days]  &         \\    
\hline
 27943.5114&  0.010 & $ -23962\,\;\;$  & 0.0890& 0.0224 &1\\
 28545.3648&  0.012 & $ -23172\,\;\;$  & 0.0600&$-$0.0037 &1\\
 39330.0455&  $-$     & $ -9016.5     $  &$-$0.0014&$-$0.0134 &2\\
 39331.9516&  $-$     & $  -9014\,\;\;$  & 0.0000&$-$0.0120 &2\\
 39341.8572&  $-$     & $  -9001\,\;\;$  & 0.0012&$-$0.0107 &2\\
 43574.8358&  0.0002 & $  -3445\,\;\;$  &$-$0.0057& 0.0026 &3\\
 46199.5059&  0.0003 & $      0\,\;\;$  & 0.0000& 0.0209 &4\\
 46201.4110&  0.0005 &     2.5       & 0.0004& 0.0213 &4\\
 46569.3960&  0.0003 &   485.5       &$-$0.0009& 0.0218 &4\\
 46598.3489&  0.0003 &   523.5       &$-$0.0007& 0.0235 &4\\
 48070.6727&  0.0002 & $   2456\,\;\;$  &$-$0.0018& 0.0281 &5\\
 48071.8152&  0.0002 &  2457.5       &$-$0.0021& 0.0278 &5\\
 48072.5777&  0.0002 &  2458.5       &$-$0.0015& 0.0284 &5\\
 48704.1699&  0.0011 &  3287.5       &$-$0.0048& 0.0281 &6\\
 48704.5510&  0.0018 & $   3288\,\;\;$  &$-$0.0047& 0.0282 &6\\
 52385.9046&  0.0035 & $   8120\,\;\;$  &$-$0.0381& 0.0125 &7\\
\hline
\end{tabular}
\end{center}

Source 1: from the data by Plaut (1948) two groups were formed and their
mean values are listed, 2: Leung (1974), 3: Andersen et al. (1980),
4: Bell \& Malcolm (1987), 5: Lorenz et al. (1991), 6: HIPPARCOS; ESA (1997); 
a time is given in the Hipparcos Catalogue, here we give 
times calculated from two minima covered by HIPPARCOS photometry, 
7:~this paper.

\end{table}
}

\IBVSfig{6.6cm}{5293-f1.eps}{$O - C$ graph of V701~Sco.}


\vspace*{-1cm}

\references

Andersen, J., Nordstr\"om, B., \& Wilson, R.E., 1980, {\it A\&A}, {\bf 82}, 225

Bell, S.A., \& Malcolm, J., 1987, {\it MNRAS}, {\bf 226}, 899

Bruton, J.R., \& Chambliss, C.R., 1985, {\it IBVS}, No.\ 2805

ESA 1997, {\it Hipparcos and Tycho Catalogue}, ESA SP-1200, Noordwijk

Leung, K.-Ch., 1974, {\it A\&AS}, {\bf 13}, 315

Lorenz, R., Mayer, P., \& Drechsel, H., 1991, {\it IBVS}, No.\ 3629

Plaut, L., 1948, {\it Leiden Ann.}, {\bf 20}, 1

\endreferences


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