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\IBVShead{4544}{12 January 1998}

\IBVStitletl{DETERMINING THE PERIOD OF AN ECLIPSING BINARY:}{ V1094 T\lowercase{au} = DHK41}

\IBVSauth{Daniel H. KAISER$^1$, Gary FREY$^2$}

\IBVSinst{Crescent Moon Observatory, 2631 Washington Street, Colombus, IN 47201,
USA}
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\IBVSinsto{e-mail: kaiser@iquest.net}
\IBVSinst{North Pines Observatory, P.O. Box 1114, Mayer, Arizona, 86333, USA}
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\IBVSinsto{e-mail: gfreynpo@primenet.com}

\SIMBADobj{V1094 Tau}

\begintext              

	V1094 Tau = DHK41 = SAO 76494 is a ninth-magnitude star of spectral type
G0 at RA 4\hr 9\mm 6\sec\ DEC +21\deg 49\arcm 11\arcs\ (1950).  It was discovered to be an eclipsing
variable by Kaiser  in October 1994 from  patrol photographs.  A period of
3.176 day was published  after several eclipses were observed
visually (Kaiser 1994).  Initially it was thought to be a possible member of the
Hyades star cluster.  Subsequent analysis suggests that if true, it would be on
the outer reaches of the far side of the cluster.

 	Continued visual and photoelectric observations in 1995 revealed that
the 3.17 day period was actually not the true period, but the interval between
the secondary minimum and the following primary minimum in an eccentric orbit.
Using the time of the discovery photograph, two visual and three photoelectric
times of minima a new period of 4.49407 day was published (Kaiser
et al., 1995). 

	In 1996 Larry Marshall, of Gettysburg College, informed us that his
colleagues had been conducting a radial velocity study of this system and that
the 4.49 day period was actually in error and that the true period is double
that figure (Marshall, 1996).  Doubling the period revealed that all
observations to date fit both periods.  The main change in the light
curve was to shift the secondary eclipse from phase 0.3 to phase 0.65.  The
other obvious change was to widen the observational gaps in the light curve.   

	In January of 1997 two new times of minimum were determined by the Kwee--Van Woerden (1956) method.  The first by Frey using his
.51 meter telescope and SSP3 photoelectric photometer.  The second by Kaiser
using his .35 meter telescope and ST6 CCD.  GSC\,1263 606 was used as an
comparison star in both cases. These data were combined with the earlier times
for a least squares solution.  The photoelectric/CCD data were given a weight of
10, the visual data 2, and the discovery photograph 1.  The result refined the
period to the sixth decimal.   Table 1 lists the new O$-$C's.  Figures 1 and 2 plot the data from Kaiser et al. phased to the new period.

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New Elements\ \ \ Min.\,I = JD\,2\,449\,701.7059 + 8\fday 988487$\times$ E \hfill (1)
\hspace*{67mm}   $\pm$0.0003 $\pm$\ 0.000007                                        \vskip 2mm
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\IBVSfig{9cm}{4544-f1.ps}{}

\IBVSfig{9.5cm}{4544-f2.ps}{}

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	Observations spanning nearly 100 cycles show that V1094 Tau is an Algol
type eclipsing binary with an eccentric orbit, apparently equal eclipses with a
period very close to nine days exactly.  All of these factors contributed to the
difficulty in determining the true period.  With a spectral type of G0, it just
qualifies as one of  a handful of known detached late-type main-sequence
eclipsing binaries.


\vskip 3mm

\begin{table}
\caption{Comparison of  observed minus calculated times of minima}
\begin{center}
\begin{tabular}{lrrl}
\hline                      
    HJD    &   Epoch&       O$-$C  &              Observer\\
\hline
\\
49602.846&	$-$11	  &    +0.013        &     Kaiser discovery ptg\\
49656.762&	 $-$5	  &     0.001        &     Baldwin visual\\
49683.727&       $-$2	  &  $-$0.002        &     Baldwin visual\\
49701.7061&	  0	  &     0.000        &     Terrell  pep\\
49710.6950&	 +1	  &     0.001        &     Kaiser  pep\\
49755.6355&      +6	  &  $-$0.001        &     Kaiser  pep\\
50456.7393&	+84	  &     0.000        &     Frey  pep\\
50474.7156&	+86	  &     0.000        &     Kaiser CCD\\
\hline
\end{tabular}
\end{center}
\end{table}
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\references

Marshall, L., 1996, private communication

Kaiser, D.H., 1994, {\it Inf. Bull. Var. Stars}, No.\,4119

Kaiser, D.H., Terrell, D., Baldwin, M.E., Gunn, J., Stephan, C.,  and Hakes,
B., 1995,  {\it Inf. Bull. Var. Stars}, No.\,4168

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


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