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\begin{document}
\IBVShead{4466}{11 April 1997}

\centerline{\ft SA98-185(=HD\,292574) - A NEW ECLIPSING BINARY}
\centerline{\ft AMONG LANDOLT'S STANDARD STARS} 
\vskip 8mm

\begintext

We present observational results of a newly discovered eclipsing binary
SA98-185 (=HD\,292574, RA$_{2000}$ = 6\fh 52\fmm 01\fss 85, DEC$_{2000}$ = 
$-$00\degr 27\farcmm 21\farcs 7, A2). It is one of well observed stars 
in the Landolt's (1983, 1992) standard star list, being widely used 
in the UBVRI photometry (for examples, Menzies {\it et al.} 1991 and Richer {\it et al.} 1985).

During the observing runs at Siding Spring Observatory (SSO) from November 5, 1996 to March 4, 1997, 
abnormal data points of SA98-185 were detected on February 28, 1997 
(HJD2450508.07) for the first time.
The brightness decreased by $\sim$0\fm 06 in the B, V, I magnitudes relative to that of the other 
standard stars (see Figure 2, upper panel).
The field of view of SSO 40\farcss\ telescope ($f/8$) with SITe $2048 \times 2048$ CCD is
20\farcm 6 $\times$ 20\farcm 6 and covers the whole area of SA98 which contains many well observed standard stars.

We carried out time-series CCD observations of SA98-185 over four nights from March 13 to 29, 1997 
at the Bohyunsan Optical Astronomy Observatory (BOAO) in order to detect its light variability.
These observations were done with a TEK1024 CCD camera attached to the BOAO 1.8m telescope.
The field of view in the CCD image is 5\farcm 8 $\times$ 5\farcm 8 at the f/8 Cassegrain focus of the telescope. 
Three comparison stars (SA98-193, 666 and 688; see Table 1) were monitored to check the light variability of 
SA98-185 (Figure 1).

The CCD preprocessings such as bias subtraction and flat fielding were made with the IRAF/CCDRED package.
We adopted simple aperture photometry to obtain instrumental magnitudes, using the IRAF/DAOPHOT
package (Massey \& Davis 1992) and transformed to the standard system as follows:
\vskip -2mm
$$ B (V) = {\it b (v)} + a_1 + a_2 \times X + a_3 \times (B-V) + a_4 \times (B-V) \times X $$

\noindent
where $B (V)$ and ${\it b (v)}$ are standard and instrumental magnitudes and {\it X } is the airmass. 
Four coefficients of $a_1$, $a_2$, $a_3$ and $a_4$ are zero level, primary extinction, color and secondary
extinction term, respectively. We then obtained differential magnitudes of SA98-185 which are plotted in Figure 2 and listed in Table 2 ($\Delta$B and
$\Delta$V in the sense Var--C1, $\Delta$I in the sense of Var--C2).

\vskip 3mm

\centerline{Table 1. Photometric properties of observed stars (Landolt, 1992)}
\vskip 1mm
\begin{center}
\begin{tabular}{ccrrr}
\hline
\noalign{\smallskip}
\hskip 5mm ID$_{ours}$ & Star Name \hskip 10mm & \hskip 10mm V \hskip 10mm & \hskip 10mm B$-$V \hskip 10mm 
& \hskip 10mm U$-$B \hskip 10mm \\
\noalign{\smallskip}
\hline
\noalign{\smallskip}
Var  & SA98-185 &  10.536 & 0.202 & 0.113  \\
C1 & SA98-193 &  10.030 & 1.180 & 1.152  \\
C2 & SA98-666 &  12.732 & 0.164 & $-$0.004  \\
C3 & SA98-688 &  12.754 & 0.293 & 0.245  \\
\noalign{\smallskip}
\hline
\end{tabular}
\end{center}
\vfill
\eject

\centerline{2}
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\epsfysize=10cm
\centerline{\epsffile{4466-f1.ps}}
\begin{center}
Figure 1. A CCD frame (5\farcm 8 $\times$ 5\farcm 8) of SA98-185 observed in the BOAO. Three comparison stars 
(SA98-193, 666 and 688) are denoted by their number
\end{center}

\epsfysize=10.2cm
\centerline{\epsffile{4466-f2.ps}}
\begin{center}
Figure 2. Light variations of SA98-185 observed at SSO (upper panel) and BOAO(lower panel). It is noted that the brightness of SA98-185 decreased by about 0\fm 06 in B and V near HJD\,2450508.07 and by 0\fm 14 in B near HJD\,2450521.04
\end{center}

\eject

\centerline{3}

\centerline{Table 2. Differential magnitudes of SA98-185}
\small
\begin{center}
\begin{tabular}{cccccccccc}
\hline
HJD & $\Delta$ B & HJD& $\Delta$ B & HJD & $\Delta$ B & HJD & $\Delta$ V & HJD & $\Delta$ I \\
\hline
2450000.+&        & 520.9896 & $-$0.459 & 521.0369 & $-$0.334 & 2450000.+&        & 2450000.+&        \\
393.1518 & $-$0.469 & 520.9902 & $-$0.462 & 521.0374 & $-$0.336 & 393.1430 & +0.522 & 393.1231 & $-$2.215 \\
393.1547 & $-$0.476 & 520.9909 & $-$0.460 & 521.0380 & $-$0.333 & 393.1456 & +0.522 & 393.1255 & $-$2.223 \\
393.1577 & $-$0.473 & 520.9915 & $-$0.455 & 521.0389 & $-$0.326 & 393.1487 & +0.516 & 393.1303 & $-$2.238 \\
393.2190 & $-$0.472 & 520.9921 & $-$0.454 & 521.0396 & $-$0.325 & 394.2323 & +0.503 & 393.1328 & $-$2.236 \\
393.2219 & $-$0.472 & 520.9928 & $-$0.455 & 521.0401 & $-$0.331 & 457.2027 & +0.503 & 393.1366 & $-$2.207 \\
396.2363 & $-$0.460 & 520.9934 & $-$0.456 & 521.0407 & $-$0.328 & 458.1895 & +0.521 & 393.1390 & $-$2.240 \\
458.2010 & $-$0.467 & 520.9943 & $-$0.453 & 521.0413 & $-$0.325 & 458.1919 & +0.513 & 393.2301 & $-$2.230 \\
458.2034 & $-$0.470 & 520.9951 & $-$0.453 & 521.0419 & $-$0.323 & 507.9734 & +0.512 & 393.2326 & $-$2.235 \\
507.9708 & $-$0.483 & 520.9957 & $-$0.457 & 521.0425 & $-$0.325 & 508.0717 & +0.572 & 394.2025 & $-$2.223 \\
508.0690 & $-$0.435 & 520.9962 & $-$0.451 & 521.0430 & $-$0.326 & 510.9329 & +0.512 & 396.2302 & $-$2.209 \\
512.0770 & $-$0.486 & 520.9968 & $-$0.451 & 521.0438 & $-$0.327 & 512.0799 & +0.520 & 457.2037 & $-$2.203 \\
520.9539 & $-$0.466 & 520.9974 & $-$0.448 & 521.0443 & $-$0.328 & 534.9655 & +0.503 & 458.1924 & $-$2.220 \\
520.9554 & $-$0.467 & 520.9980 & $-$0.448 & 521.0449 & $-$0.327 & 534.9661 & +0.512 & 458.1947 & $-$2.204 \\
520.9565 & $-$0.464 & 520.9986 & $-$0.445 & 521.0455 & $-$0.330 & 534.9664 & +0.513 & 507.9776 & $-$2.221 \\
520.9581 & $-$0.462 & 520.9991 & $-$0.439 & 521.0461 & $-$0.325 & 535.0140 & +0.516 & 508.0757 & $-$2.162 \\
520.9587 & $-$0.459 & 520.9997 & $-$0.444 & 534.9604 & $-$0.471 & 535.0155 & +0.520 & 508.9356 & $-$2.233 \\
520.9591 & $-$0.458 & 521.0003 & $-$0.441 & 534.9618 & $-$0.467 & 535.0159 & +0.517 & 509.0682 & $-$2.221 \\
520.9596 & $-$0.458 & 521.0015 & $-$0.440 & 534.9627 & $-$0.468 & 535.0530 & +0.521 & 510.9347 & $-$2.225 \\
520.9601 & $-$0.460 & 521.0030 & $-$0.439 & 535.0109 & $-$0.458 & 535.0540 & +0.523 & 511.0626 & $-$2.203 \\
520.9605 & $-$0.463 & 521.0042 & $-$0.434 & 535.0118 & $-$0.459 & 535.0544 & +0.522 & 511.9300 & $-$2.247 \\
520.9612 & $-$0.462 & 521.0051 & $-$0.426 & 535.0124 & $-$0.460 & 535.9592 & +0.497 \\
520.9619 & $-$0.463 & 521.0058 & $-$0.422 & 535.0504 & $-$0.437 & 535.9621 & +0.507 \\
520.9623 & $-$0.460 & 521.0064 & $-$0.423 & 535.0514 & $-$0.445 & 535.9649 & +0.504 \\
520.9628 & $-$0.460 & 521.0070 & $-$0.420 & 535.0521 & $-$0.441 & 535.9677 & +0.503 \\
520.9633 & $-$0.457 & 521.0076 & $-$0.418 & 535.9577 & $-$0.472 & 535.9707 & +0.499 \\
520.9637 & $-$0.459 & 521.0081 & $-$0.418 & 535.9608 & $-$0.467 & 535.9733 & +0.504 \\
520.9652 & $-$0.463 & 521.0093 & $-$0.418 & 535.9634 & $-$0.473 & 535.9759 & +0.502 \\
520.9666 & $-$0.468 & 521.0102 & $-$0.416 & 535.9663 & $-$0.470 & 535.9785 & +0.497 \\
520.9681 & $-$0.461 & 521.0107 & $-$0.418 & 535.9694 & $-$0.473 & 535.9815 & +0.497 \\
520.9694 & $-$0.462 & 521.0112 & $-$0.411 & 535.9720 & $-$0.476 & 535.9843 & +0.506 \\
520.9700 & $-$0.458 & 521.0117 & $-$0.413 & 535.9747 & $-$0.476 & 535.9874 & +0.504 \\
520.9705 & $-$0.465 & 521.0123 & $-$0.410 & 535.9773 & $-$0.479 & 535.9902 & +0.499 \\
520.9710 & $-$0.463 & 521.0143 & $-$0.401 & 535.9800 & $-$0.470 & 535.9928 & +0.510 \\
520.9714 & $-$0.463 & 521.0151 & $-$0.393 & 535.9830 & $-$0.475 & 535.9955 & +0.504 \\
520.9719 & $-$0.464 & 521.0160 & $-$0.392 & 535.9862 & $-$0.477 & 535.9982 & +0.504 \\
520.9723 & $-$0.461 & 521.0165 & $-$0.389 & 535.9889 & $-$0.472 & 536.0009 & +0.505 \\
520.9732 & $-$0.454 & 521.0170 & $-$0.388 & 535.9915 & $-$0.466 & 536.0037 & +0.507 \\
520.9738 & $-$0.461 & 521.0175 & $-$0.387 & 535.9942 & $-$0.475 & 536.0081 & +0.517 \\
520.9743 & $-$0.461 & 521.0180 & $-$0.393 & 535.9969 & $-$0.470 & 536.0120 & +0.509 \\
520.9748 & $-$0.467 & 521.0202 & $-$0.383 & 535.9996 & $-$0.477 & 536.0161 & +0.504 \\
520.9752 & $-$0.462 & 521.0207 & $-$0.377 & 536.0024 & $-$0.476 & 536.0200 & +0.505 \\
520.9757 & $-$0.458 & 521.0212 & $-$0.377 & 536.0061 & $-$0.480 & 536.0238 & +0.507 \\
520.9762 & $-$0.465 & 521.0217 & $-$0.378 & 536.0100 & $-$0.474 & 536.0275 & +0.505 \\
520.9767 & $-$0.459 & 521.0223 & $-$0.371 & 536.0142 & $-$0.474 & 536.0317 & +0.510 \\
520.9772 & $-$0.463 & 521.0233 & $-$0.370 & 536.0182 & $-$0.469 & 536.0363 & +0.507 \\
520.9776 & $-$0.462 & 521.0241 & $-$0.367 & 536.0258 & $-$0.473 & 536.0400 & +0.512 \\
520.9781 & $-$0.462 & 521.0247 & $-$0.362 & 536.0296 & $-$0.466 & 536.0441 & +0.499 \\
520.9786 & $-$0.465 & 521.0253 & $-$0.364 & 536.0345 & $-$0.478 & 536.0479 & +0.518 \\
520.9792 & $-$0.451 & 521.0259 & $-$0.359 & 536.0382 & $-$0.472 & 536.0516 & +0.519 \\
520.9798 & $-$0.452 & 521.0265 & $-$0.355 & 536.0418 & $-$0.470 & 536.0551 & +0.513 \\
520.9802 & $-$0.452 & 521.0273 & $-$0.352 & 536.0461 & $-$0.474 & 536.0589 & +0.522 \\
520.9807 & $-$0.462 & 521.0281 & $-$0.350 & 536.0498 & $-$0.470 & 536.0626 & +0.524 \\
520.9811 & $-$0.455 & 521.0287 & $-$0.345 & 536.0534 & $-$0.457 & 536.0663 & +0.530 \\
520.9816 & $-$0.449 & 521.0292 & $-$0.357 & 536.0571 & $-$0.471 & 536.9469 & +0.534 \\
520.9820 & $-$0.460 & 521.0298 & $-$0.351 & 536.0608 & $-$0.460 & 536.9487 & +0.530 \\
\hline
\end{tabular}
\end{center}

\large
\vfill
\eject
\centerline{4}
\centerline{Table 2 (cont.)}
\small
\begin{center}
\begin{tabular}{cccccccccc}
\hline
HJD & $\Delta$ B & HJD& $\Delta$ B & HJD & $\Delta$ B & HJD & $\Delta$ V\\
\hline
2450000.+&        & 520.9896 & $-$0.459 & 521.0369 & $-$0.334 & 2450000.+&  \\  
520.9825 & $-$0.456 & 521.0304 & $-$0.344 & 536.0645 & $-$0.462 & 536.9502 & +0.523 \\
520.9830 & $-$0.462 & 521.0310 & $-$0.345 & 536.9461 & $-$0.460 & 536.9519 & +0.524 \\
520.9834 & $-$0.464 & 521.0316 & $-$0.342 & 536.9480 & $-$0.453 & 536.9548 & +0.522 \\
520.9839 & $-$0.455 & 521.0324 & $-$0.342 & 536.9495 & $-$0.456 & 536.9577 & +0.516 \\
520.9851 & $-$0.459 & 521.0330 & $-$0.341 & 536.9512 & $-$0.457 & 536.9598 & +0.513 \\
520.9859 & $-$0.452 & 521.0338 & $-$0.343 & 536.9532 & $-$0.452 & 536.9626 & +0.510 \\
520.9868 & $-$0.457 & 521.0346 & $-$0.340 & 536.9566 & $-$0.463 & 536.9643 & +0.514 \\
520.9877 & $-$0.461 & 521.0351 & $-$0.340 & 536.9586 & $-$0.458 &          &        \\
520.9883 & $-$0.461 & 521.0357 & $-$0.337 & 536.9612 & $-$0.465 &          &        \\
520.9890 & $-$0.457 & 521.0363 & $-$0.337 & 536.9636 & $-$0.470 &          &        \\
\hline
\end{tabular}
\end{center}

\vskip 2mm
\large
Light variations of SA98-185 were clearly detected on one night (HJD\,2450521.0). 
Its brightness started decreasing at HJD\,2450520.99, then reached  minimum near HJD 2450521.042 and
then slightly increased again (Figure 2). The light curves are similar to that of an Algol-type 
eclipsing binary (Hoffmeister {\it et al.} 1985). Its binary nature can be also deduced from the 
SSO data which showed a similar brightness decrease of about 0\fm 06 in all filters (B, V and I).

Light variations of SA98-185 have not been reported before (Kholopov {\it et al.} 1988). 
The UBVRI photometry performed by Landolt (1992) for 37 nights (45 data points) did not show any peculiarity 
of SA98-185 and gave very low mean errors of magnitudes and colors (for example, V=10.536$\pm$0.0018).
However, our observations suggest that it is a detached eclipsing binary with a minimum brightness
near HJD\,2450521.042, and an amplitude of at least 0\fm 14 in the blue band. 

\vskip .4cm

\beginauthors
S.-L. KIM$^1$
H. SUNG$^2$
S.-G. LEE$^1$
$^1$Korea Astronomy Observatory
Taejon, 305-348, Korea
e-mail : slkim@seeru.boao.re.kr
\vskip 1mm
$^2$Visiting Fellow, MSSSO, 
Australian National University, Australia 
\endauthors
\vskip -5mm
%\vskip - 5mm
\references

Hoffmeister, C., Richter, G., Wenzel, W., 1985, in {\it Variable stars}, p.\,201

Kholopov, P.N., Samus', N.N., Frolov, M.S., Goranskij, V.P., Gorynya, N.A., Kireeva, N.N., Kukarkina, N.P., Kurochkin, N.E., Medvedeva,  G.I., Perova, N.B., Shugarov, S.Yu. 1985-1988, {\it General Catalogue of 
Variable Stars}, 4th Edition (Moscow: Nauka Publishing House)

Landolt, A.U., 1983, {\it AJ}, {\bf 88}, 439

Landolt, A.U., 1992, {\it AJ}, {\bf 104}, 340

Massey, P., Davis, L.E., 1992, {\it A User's Guide to Stellar CCD photometry with IRAF}

Menzies, J.W., Marang, F., Laing, J.D., Coulson, I.M., Engelbrecht, C.A., 1991, {\it MNRAS}, {\bf 248}, 642

Richer, H.B., Pritchet, C.J., Crabtree, D.R., 1985, {\it ApJ}, {\bf 298}, 240

\vskip 4mm
\centerline{\bf ERRATUM}
\vskip 1mm

In the printed version the affiliation for author S.-G. LEE was erroneously
given as "3".

\end{document}
