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\input ibvs2.sty
\begin{document}

\IBVShead{4914}{20 June 2000}

\IBVStitle{A New Eclipsing Binary in the Field of LHS 2176 and 2178} 

\IBVSauth{Robb, R.M.$^1$; Delaney, P.A.$^2$; Edalati, M.T.$^3$; Balam, D.D.$^4$; Berndsen, A.}

\IBVSinst{Guest User, Canadian Astronomy Data Centre, which is operated by
the Herzberg Institute of Astrophysics, National Research Council of
Canada}

\IBVSinst{York University, Toronto, Canada, Internet: pdelaney@yorku.ca}

\IBVSinst{Ferdowsi University of Mashhad, Mashhad, Iran,
Internet: eda@science1.um.ac.ir}

\IBVSinst{Guest Observer, Dominion Astrophysical Observatory, which is
operated by the Herzberg Institute of Astrophysics, National Research
Council of Canada}

\IBVSinsto{Climenhaga Observatory, Dept.\ of Physics and Astronomy, 
University of Victoria, Victoria, BC, Canada, V8W 3P6, 
Internet: robb@uvic.ca}

\IBVSabs{ USNO1575-03003814 is a near contact eclipsing }
\IBVSabs{ binary star with deep eclipses and an orbital period of 0.3234 days.}

\SIMBADobj{USNO-A1.0 1575-03003814}

\IBVStyp{ EW }

\IBVSkey{ stars: activity}
\IBVSkey{ binaries: close}
\IBVSkey{ binaries: eclipsing}

\begintext

The nearby stars LHS 2178 = GJ 362 = GSC 4386\_1592 and LHS 2176 = GJ
360~= =~GSC 4386\_1705 have had their properties summarized by H\"unsch
et al.\ (1999), including their visual and X-ray brightnesses, colors,
spectral types, and distances. Panagi and Mathioudakis (1993) report
H$\alpha$ emission in LHS 2178. We observed these stars in a
continuing search for photometric variations in active stars.

\IBVSfig{6.5cm}{4914-f1.ps}{Finder chart labeled with the GSC
numbers and an $*$ to denote USNO1575--03003814.}

Figure 1 shows the field of stars observed with the automated 0.5m telescope
of the Climenhaga Observatory at the University of Victoria and reduced in a
fashion similar to that described in Robb and Greimel (1999). Table 1 lists
the stars' identification numbers, coordinates (J2000) and magnitudes from the
Hubble Space Telescope Guide Star Catalog (GSC) (Jenkner et al.\ 1990). 
Initially observations were made in R$_c$ and I$_c$, but to increase the
signal to noise ratio we were forced to observe with no filter, which we
designate with a ``C". From standard star observations we found that our
system with no filter had a very wide passband with a center wavelength close
to that of Cousins R, but with 3.5 times the flux. Our differential $\Delta$C
magnitudes are calculated in the sense of the star minus LHS2178. For each
star the mean of the nightly means is shown as $\Delta$C in Table 1. The
standard deviation of the nightly means is a measure of the night to night
variations and is called ``Std Dev Between" in Table 1. Brightness variations
during a night were measured by the standard deviation of the differential
magnitudes and are listed for the most photometric night in the last column as
``Std Dev Within".

\begin{table}
\caption{Stars observed in the field of LHS2178}
\begin{center}
\begin{tabular}{ccccrcc}
\hline
\lower6pt\hbox{GSC No.} & R.A. & Dec. & GSC & \multicolumn1c{$\Delta$C} & Std Dev & Std Dev \\[-3pt]
 & J2000 & J2000 & Mag. & \multicolumn1c{Mag.} & Between & Within \\
\hline
4386\_1592 & $09\hr42\mm54\sec$ & $+70\deg$02\arcm26\arcs & 10.8 & \multicolumn1c- & - & - \\ 
4386\_1705 & $09\hr42\mm37\sec$ & $+70\deg$02\arcm06\arcs & 10.2 & $-0.539$ & 0.016 & 0.002\\ 
4383\_1198 & $09\hr43\mm16\sec$ & $+69\deg$59\arcm44\arcs & 13.8 & 3.875 & 0.031 & 0.011\\ 
USNO1575--03003814 & $09\hr43\mm09\sec$ & $+70\deg$00\arcm09\arcs & 15.4 & 5.159 & 0.130 & - \\ 
4386\_1682 & $09\hr43\mm10\sec$ & $+70\deg$01\arcm23\arcs & 14.6 & 4.867 & 0.098 & 0.029\\ 
4386\_1855 & $09\hr42\mm24\sec$ & $+70\deg$04\arcm12\arcs & 14.5 & 5.020 & 0.090 & 0.035\\ 

\hline
\end{tabular}
\end{center}
\end{table}

From the plots of individual night's data we observed no significant
variations in LHS 2178 or LHS 2176. From night to night there were variations
larger than we would have expected, however the comparison stars are so faint
that we cannot claim to have seen photometric variations on a daily time
scale.

The star USNO1575--03003814 (Monet et al.\ 1996) had obvious variations
during a night and is a new eclipsing binary star.
There is no ambiguity in the determination of its orbital period,
since two of the nights contain more than one minimum.
Using data points within 0\fday04 of the minimum,
and the method of Kwee and van Woerden (1956), 
the heliocentric Julian Dates of minimum brightness were found and are
listed in Table 2 with a letter indicating the filter used. 

\begin{table}[h]
\caption{Times of Minimum (HJD${}-{}$2451000) of USNO1575--03003814 }
\begin{center} 
\begin{tabular}{lllllll}
\hline
Primary & 643.7333R & 651.8163C & 652.7902I & 653.7574C & 671.8686C & 672.8403C\\
Secondary & 643.8984R & 652.9475I & 677.8507C & 680.7647C & & \\
\hline
\end{tabular}
\end{center}
\end{table}

Assuming the secondary minima are at phase 0.5, a fit to these times gives the
ephemeris:
$$
{\rm HJD~of~Primary~Minimum} = 2451643\fday7333(10) + 0\fday32340(3) \times E.
$$
where the uncertainties in the final digit are given in brackets
and the root mean square error of the fit is 0\fday0021.
The 947 differential (LHS 2178${}-{}$USNO1575--03003814 ) unfiltered
magnitudes phased at this period are plotted in Figure 2 with different 
symbols for each of the nights. The large scatter is attributable to the
faintness of the object.

To ascertain the temperature and brightness of the variable star, CCD
frames of the field were obtained with $B$, $V$, R$_c$ and I$_c$ filters.
The stars LHS 2178 and LHS 2176 have $B$, $V$, R$_c$ and I$_c$ magnitudes
measured by Weis (1996), thus allowing us to transform our observed
magnitudes to the standard Cousins system. For USNO1575--03003814 this
yields values of $V=15.43\pm.10$ and $B-V=1.04\pm.10$,
$V-R=0.53\pm.10$, $V-I=0.86\pm.10$ at maximum light. The reddening
would be $E_{B-V}=0.132$, $E_{V-I}=0.182$ with an extinction of
about $A_v=0.439$ (Schlegel et al.\ 1998).
From the dereddened colors we estimate the spectral class of
USNO1575--03003814 to be approximately K0V (Cousins 1981).

\IBVSfig{7cm}{4914-f2.ps}{Unfiltered light curve of USNO1575--03003814 for
spring 2000}

\IBVSfig{6.5cm}{4914-f3.ps}{Unfiltered normal points with curve from an
example model of the eclipsing system}

While the true nature of this system cannot be determined from these
data, a model can be found using reasonable parameters. The light
curve leads us to expect this to be a near-contact system. Using
Binmaker 2.0 (Bradstreet 1993), the model light curve as shown in
Figure 3 was made. We assumed a temperature of 4900K for the primary
and a mass ratio of 0.95. A satisfactory fit to the data was found
with an inclination of $71.5\deg$ and a temperature of the secondary
star 500K cooler than the primary star. Two main-sequence stars of
this temperature difference would have a mass ratio of 0.95. The
eclipses are then well fit with the stars just touching the inner
critical surface of the Roche Lobe (fillout = 0.0). The uncertainty in
the inclination is about $\pm2\deg$ and the difference in temperature
is known to about $\pm10\%$ both dependent on the assumed mass ratio.

\IBVSfig{2.5cm}{4914-f4.ps}{Three-dimensional model of the near-contact
system at phase 0.25}

The relative sizes and shapes of the components of the system
are shown in Figure 4, again using Binmaker 2.0 (Bradstreet 1993).

The absolute magnitude can be estimated from the period and
$(B-V)_0=0.91$ (Rucinski and Duerbeck 1997) and $(V-I)_0=0.68$
(Rucinski 2000) to be $M_V=4.7\pm.3$ giving a distance of
$1140\pm150$~pc. The dependence of the absolute magnitude on the color
through Rucinski's formula is nearly equal to the relationship of
extinction and the reddening making the distance determination almost
independent of the extinction.

The star USNO1575--03003814 is therefore a near-contact eclipsing
system with late-type components. Photometric observations should be
continued to monitor light curve changes due to spot migration, flares,
and period changes. Spectroscopic observations will be valuable to
determine a precise spectral class for the system and to measure radial
velocities to determine the masses and the scale of the system.

\references

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

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

H\"unsch, M., Schmitt, J.H.M.M., Sterzik, M.F., and Voges, W., 1999, 
{\it A\&A Sup}, {\bf135}, 319

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

Monet, D., Bird, A., Canzian, B., Harris, H., Reid, N., Rhodes, A., Sell,
S., Ables, H., Dahn, C., Guetter, H., Henden, A., Leggett, S., Levison,
H., Luginbuhl, C., Martini, J., Monet, A., Pier, J., Riepe, B., Stone, R.,
Vrba, F., Walker, R., 1996, USNO-A1.0, (U.S. Naval Observatory, Washington
DC).

Panagi, P.M., and Mathioudakis, M., 1993, {\it A\&A Sup}, {\bf100}, 343

Robb, R.M. and Greimel, R., 1999, {\it ASP Conf. Ser.}, {\bf 189}, 198
%Changed: Fri Jun  3 09:53:28 MEST 2005

Rucinski, S.M., and Duerbeck, H.W., 1997, {\it PASP}, {\bf109}, 1345

Rucinski, S.M., 2000, {\it AJ}, in press 

Schlegel, D.J., Finkbeiner, D.P., Davis, M., 1998, {\it ApJ}, {\bf500},
525

Weis, E., 1996, {\it AJ}, {\bf112}, 2300

\end{document}
