\documentstyle[twoside,epsf]{article}

\input ibvs2.sty
\input ibvst.sty

\begin{document}

\IBVShead{5136}{12 July 2001}

\IBVStitletl{Times of Minima of Eclipsing Binaries}{ DI Herculis and V1143 Cygni}

\IBVSauth{Dariush, A.$^1$; Afroozeh, A.$^1$; Riazi, N.$^{1,2}$}

\IBVSinst{Biruni Obs., Shiraz University, Shiraz 71454, Iran, email: dariush@phys11.susc.ac.ir}

\IBVSinst{Physics Dept., Shiraz University, Shiraz 71454, Iran, email:  riazi@sun01.susc.ac.ir}

\SIMBADobj{DI Her}
\SIMBADobj{V1143 Cyg}

\begintext

{\bf VAR 1}\smallskip\hrule

\IBVSTnam{DI Herculis = HD 175227}

\IBVSTcoo{18\hr53\mm26\fsec24}{+24\deg16\arcm40\farcs8}{J2000}

\IBVSTcomp{HD 174932}

\IBVSTchk{HD 343238}

{\bf VAR 2}\smallskip\hrule

\IBVSTnam{V1143 Cygni = HD 185912}

\IBVSTcoo{19\hr38\mm41\fsec18}{+54\deg58\arcm25\farcs7}{J2000}

\IBVSTcomp{HD 184240}

\IBVSTchk{HD 186239}

\hrule

\IBVSTobs{51-cm Cassegrainian telescope of Biruni Observatory at Shiraz University, Shiraz, Iran}

\IBVSTdet{Unrefrigerated RCA4509 photomultiplier tube}

\IBVSTfil{$B$ and $V$ bands of Johnson system}

\IBVSTsysn

\IBVSTtyp{ Eclipsing binaries with apsidal motion }

\IBVSfig{10cm}{5136-f1.eps}{Light curve of DI Herculis in $B$ filter}

\IBVSfig{10cm}{5136-f2.eps}{Light curve of DI Herculis in $V$ filter}

\IBVSfig{10cm}{5136-f3.eps}{Light curve of V1143 Cygni in $B$ filter}

\IBVSfig{10cm}{5136-f4.eps}{Light curve of V1143 Cygni in $V$ filter}

\IBVSTrem{
DI Herculis and V1143 Cygni are stars with apsidal motion, moving in
highly eccentric orbits.  The eccentricities are 0.49 and 0.54 for DI
Herculis and V1143 Cygni, respectively (Guinan and Maloney, 1985).  The
observations were made during the summer of 2000. Heliocentric times of
minima were computed by fitting a Lorentzian function to the minima.
Uncertainties were estimated from the combined errors in the two
filters.  Table 1 presents the derived times of minima (I for primary
and II for secondary).  The depths of minima in each filter are
presented in Table 2.  The probable errors of the individual
observation were estimated from an examination of the scatter in the
outside eclipse portions of the light curves.  Finally, the observed
light curves of DI Herculis and V1143 Cygni in $B$ and $V$ filters are
plotted in Figures 1--4.  These light curves are calculated according
to the ephemeris of Guinan et al.\ (1994) for DI Herculis and of Lacy
and Fox (1994) and Andersen et al.\ (1987) for V1143
Cygni.\belowdisplayskip-12pt
$$\begin{array}{l}
{\rm Min.~I~(DI~Herculis) = HJD}~2449491.8622 +10\fday55016766 \times E; \\
{\rm Min.~I~(V1143~Cygni) = HJD}~2449234.6144 + 7\fday64075217 \times E. \\
\end{array}$$
}


\begin{table}
\caption{The photoelectric times of minima}
\begin{center}
\begin{tabular}{lcc}
\hline
\lower6pt\hbox{System} & \lower6pt\hbox{Min.~type} & Heliocentric~JD \\[-2pt]
& & 2400000\,+ \\
\hline
DI Her    & I  & $51781.25030\pm.00021$ \\
DI Her    & II & $51789.37072\pm.00081$ \\
V1143 Cyg & I  & $51771.34410\pm.00066$ \\
V1143 Cyg & II & $51792.28645\pm.00220$ \\
\hline
\end{tabular}
\end{center}

\caption{The depth of minima, according to the present study}
\begin{center}
\begin{tabular}{lccc}
\hline
System & Filter & Min.~I & Min.~II \\
\hline
DI Her    & $B$ & $0\fmm70\pm0.01$ & $0\fmm55\pm0.01$ \\
DI Her    & $V$ & $0\fmm69\pm0.02$ & $0\fmm58\pm0.02$ \\
V1143 Cyg & $B$ & $0\fmm53\pm0.01$ & $0\fmm25\pm0.01$ \\
V1143 Cyg & $V$ & $0\fmm48\pm0.02$ & $0\fmm23\pm0.02$ \\
\hline
\end{tabular}
\end{center}
\end{table}

\IBVSTack{We would like to thank Mr.~Mehdi Nazem for his help with some
of the observations.}

\references

Andersen, J., Garc\'{\i}a, J.M., Gim\'enez, A., and Nordstr\"om, B., 1987, {\it Astron.\ Astrophys.},
{\bf 174}, 107

Guinan, E.F., Maloney, F.P., 1985, {\it Astron.\ J.}, {\bf 90}, 1519

Guinan, E.F., Marshall, J.J., Maloney, F.P., 1994, {\it IBVS}, No.\ 4101

Sandberg Lacy, C.H., Fox, G.W., 1994, {\it IBVS}, No.\ 4009

\end{document}

