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\IBVShead{4405}{6 December 1996}


\centerline{\ft NEW ECLIPSING BINARY STAR CoD $-$24\degr 12698 IN THE
DIRECTION}
\centerline{\ft  OF THE STAR-FORMING REGION $\rho$ Oph}
\vskip 8mm

\begintext

The members of the Upper Scorpius region were observed by Eggen (1983) in an
extensive intermediate band and $H_{\beta}$ photometry. He detected the
variability of CoD $-$24\degr 12698 (SAO\,184441). The
star was changing its light from 10\fm 1 V (August 24, 1980) to
10\fm 3 V (September 23, 1981). In September 1980 the star had a brightness of 9\fm 4 R and 0\fm 594 R$-$I while the respective values were and 9\fm 7 and
0\fm 607 in July 1981. Herbig (see Struve and Straka, 1962) determined 
the spectral type to be A0 or A1, but found no emission in 1949. The star is
situated in the direction of the star-forming region $\rho$ Oph,
near the weak-line T Tauri stars Rox~42 and Rox~43.

We present the results taken from a long-term photometric monitoring program
for CoD $-$24\degr 12698 made during three runs from August 5, 1993 to
July 23, 1996. Our UBVR observations were obtained at the Mt. Maidanak
Observatory, Uzbekistan, using  0.48m and 0.60m telescopes equipped with
a pulse counting FEU-79 photomultiplier tubes. The mean error of a
observation is typically $\pm$ 0\fm 01 in V. CoD$-$24\degr 12690 was used as comparison star (7\fm 538 V, 0\fm 012 U$-$B,
0\fm 382 B$-$V and 0\fm 236 V$-$R).

A periodogram analysis of observations proved that CoD $-$24\degr 12698
is a short period eclipsing binary star likely of W UMa type. The ephemeris
for the primary minimum is

$$
\begin{array}{rrrrr}
{\rm Min.I=JDH}~2449204.349&+&0\fd 589352&\times&E\\
                     \pm 1&&      \pm 1&\\
\end{array}
$$

The total number of observations are 151 in U, 203 in B, 210 in V and 197
in R. We detected 11 moments of minima and they are listed in Table 1. The
light curves of the binary are shown in Figure 1. The main photometric
characteristics are given in Table 2.

\begin{center}
Table 1
\vskip 1mm
\end{center}
\begin{center}
\begin{tabular}{cccccc}
\hline\\
JDH2400000+ & E & O$-$C & JDH2400000+ & E & O$-$C \\
\hline\\
\ 49213.1855 & 15  & $-0\fd 004$ & 50243.3686 & 1763 & $-0\fd 008$\\
\ 49226.1520 & 37  & $-0.003$ & 50243.3788 & 1763 & $+0.002$\\
\ 49520.2530 & 536 & $+0.011$ & 50249.2761 & 1773 & $+0.006$\\
\ 49540.2772 & 570 & $-0.002$ & 50275.1964 & 1817 & $-0.005$\\
\ 49540.2821 & 570 & $+0.002$ & 50275.2101 & 1817 & $+0.008$\\
\ 49543.2351 & 575 & $+0.009$ & & &\\
\hline
\end{tabular}
\end{center}
\vfill \eject

\centerline{2}
\vskip 1mm
\begin{center}
Table 2
\vskip 1mm
\end{center}
\begin{center}
\begin{tabular}{ccccc}
\hline\\
Phase & V & U$-$B & B$-$V & V$-$R \\
\hline\\
\ Max   & 10.01 & 0.40 & 0.95 & 1.03 \\
\ MinI  & 10.38 & 0.49 & 1.00 & 0.96 \\
\ MinII & 10.11 & 0.40 & 0.95 & 1.03 \\
\hline
\end{tabular}
\end{center}

\epsfysize=7cm
\centerline{\epsffile{4405-f1.ps}}
\begin{center}
Figure 1. Light curves in the U,B,V and R bands for CoD  $-$24\degr 12698. \end{center}
\vskip 4mm

The change in the colors of the variable is slight. We note that the position of the binary in
the color-color diagram does not correspond to a spectrum A0. The
components of the binary may be F-G stars. Perhaps, the binary is a foreground
 object in the direction of the star-forming region $\rho$ Oph.

One of us (MMZ) was supported by Fund for Fundamental Research of Republic
Uzbekistan (Contract 33/96).

\vskip .6cm

\beginauthors
\authorsrightcol
K.N. GRANKIN
M.M. ZAKIROV
G.C. ARZUMANYANTS
S.Yu. MELNIKOV
Astronomical Institute
Astronomical str. 33, Tashkent
700052 Uzbekistan, CIS
e-mail: grankin@silk.glas.apc.org
e-mail: mamnun@astro.gov.us
\endauthors
\vskip -4mm

\references

Eggen, O.J.: 1983, {\it Mon. Not. R. Astr. Soc.}, {\bf 204}, 377

Struve, O. and Straka, W.C.: 1962, {\it Publs Astr. Soc. Pacific}, {\bf 74}, 474


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