\documentstyle[epsf]{article}

\input ibvs2.sty
\begin{document}

\IBVShead{4504}{6 August 1997}

\IBVStitle{OBSERVATIONS OF THE GSC\,3505\_677 FIELD}

\IBVSauth{R.M. ROBB, R. GREIMEL, J. OUELLETTE}

\IBVSinsto{Climenhaga Observatory, Dept.\ of Physics and Astronomy, University of Victoria, Victoria, BC, Canada, VSW 3P6, Internet: robb@uvic.ca}

\IBVSabs{GSC 3505.677 turned out to be a new eclipsing variable.}

\SIMBADobj{GSC 3505-677}
\IBVStyp{ EW }
\IBVSkey{photometry}

\begintext

We observed the field containing one of the objects, (16548-39) = GSC
3505\_497, found in a survey by Beers et al.\ (1994I, who concluded from
objective prism spectral observations that it was  ``a medium faint star
displaying moderate to strong CaII H\&K and Balmer emission''.

The automated 0.5-m telescope, Cousins V, R and I filters and CCD camera of
the Climenhaga Observatory of the University of Victoria (Robb and
Honkanen, 1992) were used to make photometric observations of the stars.
Using IRAF\footnote{IRAF is distributed by National Optical Astronomy
Observatories, which is operated by the Association of Universities for
Research in Astronomy, Inc., under contract to the National Science
Foundation} routines, the frames were de-biased and flat-fielded, and the
magnitudes were found from 6 arc second aperture photometry using
the Gaussian centering option of the PHOT package.

\IBVSfig{6cm}{4504-f1.ps}{Finder chart of the field labeled with the GSC numbers (Jenkner et al., 1990)}
\vskip -3mm

The field of stars is shown in Figure 1 and
their designations, coordinates (J2000) and magnitudes from
the Hubble Space Telescope Guide Star Catalog (GSC) (Jenkner et al., 1990)
and the measured $\Delta$R magnitudes are tabulated in Table 1.
The $\Delta$R differences in magnitude are found from our data in the
sense of the star minus GSC\,3505\_403.
To look for brightness variations during a night the standard deviation of
the differential\break
\vfill
\eject

\begin{table}
\caption{Stars observed in the field of GSC\,3505\_677}
\begin{center}
\begin{tabular}{cccccccc}
\hline
GSC No. & RA & Dec. & GSC & $\Delta$R & V & V$-$R$_C$ & R$-$I$_C$\\
  & J2000.&J2000.& Mag.& Mag. \\
\hline
3505\_497&
$16\hr32\mm18\sec$& $+50\deg$24\arcm50\arcs&13.3&$+1.080\pm.006$&13.24&0.36&0.38
\\
3505\_403&
$16\hr32\mm24\sec$& $+50\deg$21\arcm33\arcs&12.2&$-$&12.10&0.30&0.29\\
3505\_185&
$16\hr32\mm37\sec$& $+50\deg$20\arcm53\arcs&12.9&$+0.825\pm.006$&12.95&0.31&0.35
\\
3505\_677&
$16\hr31\mm54\sec$& $+50\deg$21\arcm10\arcs&13.3&$+1.368\pm.083$&13.52 &0.59&0.37 \\
3505\_562&
$16\hr31\mm52\sec$& $+50\deg$20\arcm23\arcs&12.2&$+0.097\pm.007$& 12.44 & 0.55&0.33\\
\hline
\end{tabular}
\end{center}
\end{table}

\noindent magnitudes for each star during a night was calculated and
ranged from 0\fmm 005 for bright stars on
a good night to 0\fmm 030 for the faint stars on poor nights.
To measure night to night variations a run mean of the eight nightly averages
was calculated and is shown as $\Delta$R in Table 1.
While the object of our initial interest, GSC\,3505\_497, proved constant,
GSC\,3505\_677 is a significantly variable star.
Due to the small field of view extinction effects were
negligible and no corrections have been made for them. No corrections
have been made to transform the $\Delta$R magnitude to a standard system.
Brightness variations in GSC\,3505\_677 were evident during each night. A least
squares fit of a single sine wave to all the the data shows a deep minimum
in $\chi^2$ at an inverse period of $7.17d^{-1}$, but a plot of the light
curve shows unequal minima which led us to double the period. By the
method of Kwee and van Woerden (1956) eleven heliocentric Julian times of
minima were found and are tabulated in Table 2.
A fit to these times gives the ephemeris:

\vspace {3mm}
\centerline{HJD of Minima = 2450624\fday 7430(5) + 0\fday 27897(2) $\times$ E.}
\vspace {3mm}

\noindent where the uncertainties in the final digit are given in brackets.
The differences of the times of minima and the ephemeris are the O$-$C
values given in Table 2.

\begin{table}
\caption{Heliocentric Julian Dates of minimum light 2450000+}
\begin{center}
\begin{tabular}{rr|rr|rr}
\hline
  &R Filter\ \ \ \ \ \ \ & &R filter\ \ \ \ \ \ \ & &I Filter\ \ \ \ \ \ \ \\
\hline
HJD & O$-$C & HJD & O$-$C & HJD & O$-$C\\
\hline
  624.7432 & .0001& 634.7865& .0005 & 649.8529 & .0024\\
  627.8118& .0001& 634.9254 & $-$.0001& 650.8259 & $-$.0010\\
  632.8325& $-$.0007& 648.7342& $-$.0005& & \\
  633.8095& $-$.0001& 648.8733& $-$.0008& & \\
  633.9494&        .0003&   &   &   & \\
\hline
\end{tabular}
\end{center}
\end{table}

A plot of the differential (GSC\,3505\_677$-$GSC\,3505\_403) R magnitudes
phased at this period is shown in Figure 2 with different symbols for each
of the nights.   I band data, observed on three nights, shows the
same light curve shape.  Forty normal points were formed from the R and
the I light curve and then the color R$-$I was found from the normals.
The maxima were approximately 0.01 redder than the minima, indicating very
little temperature difference across the star and between stars.

\vfil
\eject

\IBVSfig{8cm}{4504-f2.ps}{
R band light curve of GSC\,3505\_677 for 1997}

\IBVSfig{7.5cm}{4504-f3.ps}{R band light curve (points) with example model (line) of the contact system}

To help classify the variable star V, R and I frames were obtained under
photometric conditions along with observations of four nearby bright
standard stars (Moffett and Barnes, 1979). The V band brightness,
$(V-R)_C$, and $(R-I)_C$ colors are listed in Table 1 for the brightest
stars in our field. However great caution should be exercised in using
these data since they are derived from only a few standard stars and the
colors were transformed from the Johnson system to the Cousins system
using the equations of (Taylor, 1986). This period and $(V-I)_C$
agree very well with the short-period/blue envelope relation given
by Rucinski (1997) for W UMa systems.

\vfill 
\eject

While certainly not definitive these colors confirm that GSC 3505\_677 is
a late type (approximately K1V) star (Cousins 1981).  A dwarf star of this
color would be expected to have an absolute magnitude of approximately
V=6.2 (Allen 1976), so from our apparent magnitude of $13.52\pm.08$ at
maximum brightness, we find the distance to be about $300\pm100$ parsecs.
Using the period, $(V-I)$, relation for absolute I magnitude for contact
systems (Rucinski 1997), the distance can be found to be $400\pm60$
parsecs.

From the color information and the shape of the light curve we can
surmise that the primary star and the secondary star is a contact system.
To make an example model light curve using Binmaker 2.0 (Bradstreet 1993),
the phases of the points have been increased half a cycle and the
temperature of the large star was assumed from the $(R-I) C$ to be 4750K.
The data are best fitted with an inclination of $85\deg$, a mass ratio
of 3.45 and a fill out factor of 0.1.
The temperature of the small star was adjusted to 4820 K
to get the excellent fit seen in Figure 3.
The mass ratio and fill-out factor are correlated such that an increase
in the mass ratio of about 0.2 can be compensated by an increase in the

fill out factor by 0.1 to get nearly as good a fit.
The relative sizes and
shapes of the components of the system are shown in Figure
4, again using Binmaker 2.0.
\vskip -1cm

\IBVSfig{4cm}{4504-f4.ps}{
Three-dimensional model of the contact system at phase 0.25}
\vskip -1cm

The star GSC\,3505\ 677 is therefore a W UMa system with late type
components. Further photometric observations
will be valuable to look for period changes due to mass transfer and
to observe precise colors and thus determine the temperature of the stars.
Spectroscopic observations will be important to get a good spectral class
for the system and radial velocities will measure the scale of the system
and the masses.
RG would like to thank the Austrian Ministry of Science for financial support.
\vskip 1cm
\references

Allen, C.W., 1976, Astrophysical Quantities, the Athlone Press, Univ.
of London, UK

Beers, T.C., Bestman, W. and Wilhelm, R., 1994, {\it AJ}, {\bf108}, 268

Bradstreet, D.H., 1993, Binary Maker 2.0 Usermanual, Contact Software,
Norristown, PA 19401-5505, USA

Cousins, A.W., 1981, SAAO Circ., {\bf 6}, 4

Jenkner, H., Lasker, B., Sturch, C., McLean, B., Shara, M., Russell, J., 1990,
{\it AJ}, {\bf 99}, 2082

Kwee, K.K., van Woerden, H., 1956, {\it BAN}, {\bf 12}, 327

Moffett, T.J. and Barnes, T.G. III, 1979, {\it PASP}, {\bf 91}, 180

Robb, R.M. and Honkanen, N.N., 1992, {\it A.S.P. Conf. Ser.}, {\bf 28}, 105,
Automated Telescopes for Photometry and Imaging, ed. Adelman, Dukes and Adelman
%Original: {\it A.S.P. Conf. Ser.}, {\bf 38},
%Corrected: Tue Sep 27 09:13:06 MEST 2005

Rucinski, S.M., 1997, {\it AJ}, {\bf 113}, 407

Taylor, B.J., 1986, {\it ApJS}, {\bf 60}, 577

\end{document}
