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\IBVShead{5029}{7 February 2001}

\IBVStitle{The Short-Period Eclipsing Binary GSC 3123.1618}

\IBVSauth{Billings, G. W.$^1$; Kaiser, D. H.$^2$; Terrell, D.$^3$; Henden, A. A.$^4$}

\IBVSinst{2320 Cherokee Drive NW, Calgary, Alberta, Canada T2L
0X7, e-mail: obs681@telusplanet.net}

\IBVSinst{2631 Washington Street, Columbus, Indiana, U.S.A.
47201, e-mail: dhkaiser@sprynet.com}

\IBVSinst{Dept.\ of Space Studies, Southwest Research Institute,
1050 Walnut St., Suite 426, Boulder, Colorado, U.S.A. \\
\indent 80302, e-mail: terrell@boulder.swri.edu}

\IBVSinst{Universities Space Research Association/U.S. Naval
Observatory, P. O. Box 1149, Flagstaff, Arizona, U.S.A. \\ \indent
86002-1149, U.S.A., e-mail: aah@nofs.navy.mil}

\IBVSabs{This report discusses the nature of GSC 3123.1618}

\SIMBADobj{GSC 3123-1618}

\IBVStyp{ EW }

\begintext

Variability of the star GSC 3123-1618 = ROTSE1
J185538.25+405859.0 was detected by the ROTSE1 CCD survey
(Akerlof et al.\ 2000). Bl\"{a}ttler and Diethelm (2000) presented
an unfiltered light curve and found a period of 0\fday2559007.
Our CCD photometry during the same observing season produced a
$V$-band light curve and improved light elements.

Billings observed in the $V$ band with a 0.35-m Schmidt--Cassegrain
telescope and Apogee AP-7 CCD\@. Kaiser observed in $VRI$ with a
0.35-m Schmidt--Cassegrain and SBIG ST-9E CCD\@. Terrell observed
in $B$ with a 0.60-m Cassegrain and SBIG ST-8 CCD at the
Sommers--Bausch Observatory of the University of Colorado. Henden
observed with the 1.0-m Ritchey--Chr\'etien telescope of the U.~S.
Naval Observatory, Flagstaff Station with a Tektronix/SITe
$1024\times1024$ thinned, backside--illuminated CCD and 
${BVR_c I_c}$ filters. His photometry of the
variable near maximum light and of the comparison and check stars
is shown in Table 1 (photometry for other stars in the field can
be found in Henden 2001). Henden also used the USNO-A2.0
astrometric catalog to determine the precise position for GSC
3123-1618 of 18\hr55\mm38\fsec20, $+$40\deg58\arcm57\farcs06
(J2000).

Altogether, we obtained timings of 7 primary and 3 secondary minima
(Table~2). Times of minima were determined with the computer program
AVE (Barbera 2000) based on the Kwee--Van Woerden (1956) method. In
addition to the 10 new minima reported here, we have included 5 minima
timings published recently by Bl\"{a}ttler (2000). A least-squares
solution of the 15 timings resulted in the following light elements:
$$ \begin{array}{r@{}r@{}l}
{\rm Min.~I = HJD~} 2451766.5840 & {} + 0\fday2559067 & {} \times E.\\
\pm 0.0001 & {} \pm 0.0000001 \\
\end{array} $$

\begin{table}
\caption{${BVR_c I_c}$ photometry with errors less
than 0\fmm02, GSC 3123.1618, comparison and check stars}
\begin{center}
\begin{tabular}{cccccc}
\hline
Star & GSC & $V$ & $B-V$ & ${V-R_c}$& ${R_c-I_c}$\\
\hline
variable (max) & 3123:1618 & 13.439 & 0.990 & 0.602 & 0.556\\
comparison & 3123:0834 & 13.938 & 1.074 & 0.584 & 0.479\\
check & 3123:0596 & 13.694 & 0.671 & 0.372 & 0.331\\
\hline
\end{tabular}
\end{center}

\caption{Times of minima, GSC 3123.1618}
\begin{center}
\begin{tabular}{ccrrll}
\hline
HJD 2400000\,+ & Error $\pm$ & Epoch & $O-C$ & Observer & Type\\
\hline
51721.6729 & 0.0003 & $-$175.5 & $+$0.0005 & Kaiser & ccd${}-V$ filter\\
51722.8238 & 0.0001 & $-$171.0 & $-$0.0002 & Billings & ccd${}-V$ filter\\
51732.8043 & 0.0001 & $-$132.0 & $ $0.0000 & Billings & ccd${}-V$ filter\\
51739.8413 & 0.0002 & $-$104.5 & $-$0.0004 & Billings & ccd${}-V$ filter\\
51741.7610 & 0.0001 & $-$97.0 & $-$0.0001 & Kaiser & ccd${}-V$ filter\\
51756.7314 & 0.0005 & $-$38.5 & $-$0.0002 & Terrell & ccd${}-B$ filter\\
51756.8594 & 0.0002 & $-$38.0 & $-$0.0001 & Terrell & ccd${}-B$ filter\\
51766.4559 & 0.0005 & $-$0.5 & $-$0.0001 & Bl\"{a}ttler& ccd${}-{}$unfiltered\\
51766.5841 & 0.0005 & 0.0 & $+$0.0001 & Bl\"{a}ttler& ccd${}-{}$unfiltered\\
51771.4464 & 0.0006 & $+$19\phantom{.0} & $+$0.0002 & Bl\"{a}ttler& ccd${}-{}$unfiltered\\
51781.4271 & 0.0010 & $+$58.0 & $+$0.0005 & Bl\"{a}ttler& ccd${}-{}$unfiltered\\
51781.5543 & 0.0015 & $+$58.5 & $-$0.0002 & Bl\"{a}ttler& ccd${}-{}$unfiltered\\
51790.6392 & 0.0001 & $+$94.0 & $ $0.0000 & Kaiser & ccd${}-V$ filter\\
51864.5962 & 0.0001 & $+$383\phantom{.0} & $-$0.0001 & Billings & ccd${}-V$ filter\\
51867.6670 & 0.0001 & 395\phantom{.0} & $ $0.0001 & Billings & ccd${}-V$ filter\\
\hline
\end{tabular}
\end{center}
\end{table}

\IBVSfig{10cm}{5029-f1.eps}{Phased light curve, GSC
3123.1618${}-V$ filter}

\vskip-11pt
Henden observed on two nights, at phase 0.70, $V = 13.444$ and phase 0.26,
$V = 13.434$. We adopt the average of the two as the magnitude at
maximum, 13.439 $V$. Differential measurements yield 
14.61 $V$ in primary minimum and 14.22 $V$ in secondary minimum. The $V$-band
light curve is shown in Figure~1. Terrell used the latest
version of the Wilson--Devinney program (Wilson and Devinney 1971,
Wilson 1979) to explore preliminary solutions for the system
parameters. As expected for a light curve with partial eclipses,
the mass ratio could not be determined. A grid of solutions at
fixed values (0.5 to 1.5) of the mass ratio showed very little
variation in the goodness of fit. Until the mass ratio can be
determined by spectroscopic observations, we cannot make any
definitive claims about the nature of the system. However, our
solutions indicate that the system is in weak or broken contact.

This observing project was conducted in association with the AAVSO
eclipsing binary program. We wish to thank Marvin Baldwin,
chairman of the AAVSO Eclipsing Binary Committee, for bringing
this variable to our attention. P.R. Guilbault and D.B. Williams
assisted in preparing this report for publication. Billings
acknowledges the use of software (KAPPA, PHOTOM) provided by the
Starlink Project which is run by CCLRC on behalf of PPARC.


\IBVSedata{5029-t3.txt}

\references

Akerlof, C., et al., 2000, {\it AJ}, {\bf 119}, 1901

Bl\"{a}ttler, E., and Diethelm, R., 2000, {\it IBVS}, No.\ 4985

Bl\"{a}ttler, E., 2000, {\it BBSAG Bull.}, No.\ 123

Barbera, R., 2000, {\tt http://www.astrogea.org/soft/ave/aveint.htm}

Henden, A., 2001,\\ {\tt
ftp://ftp.nofs.navy.mil/pub/outgoing/aah/sequence/gsc3123.dat}

Kwee, K.K., and Van Woerden, H., 1956, {\it BAN}, {\bf
12}, No.\ 464, 327

Wilson, R.E., 1979, {\it ApJ}, {\bf 234}, 1054

Wilson, R.E. and Devinney, E.J., 1971, {\it ApJ}, {\bf 166}, 605

\endreferences

\end{document}
