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\IBVShead{4284}{4 January 1996}

\title{THE PERIOD OF ECLIPSING BINARY DHK\,40}

\begintext

Eclipses of the F8 type star SAO\,46698 = BD\,+49\degr 2630 were reported by Kaiser
(1994), who gave it the designation DHK 40 in his discovery list. We have
observed this variable during the past two seasons with photoelectric and CCD
photometry. DHK utilized a 35-cm Schmidt-Cassegrain telescope, Optec SSP-5
photometer, and SBIG ST-6 CCD camera, and GL used a 28-cm Schmidt-Cassegrain
and SBIG ST-6 CCD camera. A light curve compiled from DHK's photoelectric
observations (Figure 1) shows variations of Beta Lyr type with a range of 9.41
- 9.87 V.

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\centerline{Table 1. Minima of DHK\,40= SAO\,46698}
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\begin{center}
\begin{tabular}{llcrr}
\hline
\ \ \ \ \ HJD\,2400000+&    \ Obs.&  Min.&  E\ \ \ \ \ & O$-$C\ \ \\
\hline
\\
       43759.582 & H   ptg &  I &     $-$11640.0 & +0.002\\
       43777.558 & H  ptg &  I &     $-$11606.0 & $-$0.025\\
       44512.510 & H   ptg &  I &     $-$10218.0 & +0.012\\
       44733.813 & H   ptg &  I &     $-$ 9800.0 & $-$0.007\\
       45161.657 & H  ptg &  I &     $-$ 8992.0 & +0.018\\
       46590.700 & H   ptg &  I &     $-$ 6293.0 & +0.001\\
       46669.598 & H   ptg &  I &     $-$ 6144.0 & +0.005\\
       46757.468 & H  ptg &  I &     $-$ 5978.0 & $-$0.018\\
       46879.815 & H  ptg &  I &     $-$ 5747.0 & +0.019\\
       47466.464 & H   ptg &  I &     $-$ 4639.0  & +0.006\\
       49637.5821 &K   pep &  II&     $-$ 538.5  & $-$0.0011\\
\ \ \ \ \ $\pm$.0009&           &  &            &         \\
       49917.6769& K   ccd  & II        &$-$ 9.5  & $-$0.0003\\
\ \ \ \ \  $\pm$.0001&         &    &            &        \\
       49922.7073& L   ccd  & I      &     0.0  & +0.0001\\
\ \ \ \ \ $\pm$.0002&          &        &         &      \\
       49927.7383& L   ccd &  II       & + 9.5&   +0.0011\\
\ \ \ \ \ $\pm$.0006&         &          &      &          \\
       49983.5979& K  ccd &  I    &   + 115.0&   +0.0007\\
\ \ \ \ \  $\pm$.0002&         &      &          &           \\
       50001.5979& L   ccd  & I    &   + 149.0  & $-$0.0016\\
\ \ \ \ \ $\pm$0002&           &       &             &    \\
\hline
\end{tabular}
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H = Harvard plate, K = Kaiser, L = Lubcke
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\centerline{2}
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\centerline{Figure 1. Photoelectric V observations of DHK\,40 by Kaiser, 1994 season.}
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DBW examined 175 Harvard College Observatory patrol plates for the interval
1976-1989 to obtain additional times of minima. Table 1 lists 10 Harvard
plate minima and 6 high-precision PEP/CCD minima. The PEP/CCD minima were
reduced by the Kwee--Van Woerden method, and the internal error of each timing
is listed. These times were introduced into a least-squares solution, with
weight 1 for the photographic data and weight 10 for the PEP/CCD data, to
derive the following light elements:
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\hspace*{3cm}Min. I = HJD\,2\,449\,922.7072 + 0\fd 52947826 $\times$ E \hfill (1)
 \hspace*{8cm} $\pm$7 \hspace*{1.8cm}$\pm$11


The light curve shows strong proximity effects, and Maximum I (Phase 0.25) is
slightly brighter than Maximum II. DHK 40 appears to be a thermally decoupled
binary of W UMa or ``near contact" type. The reported spectral type is rather
late for a binary with such unequal minima and needs to be confirmed. We are
continuing observations to obtain a complete light curve for solution. We
wish to thank Dr. Martha Hazen for the opportunity to examine the Harvard
plates.
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\beginauthors

DANIEL H. KAISER
Crescent Moon Observatory
2631 Washington Street
Columbus, IN 47201 U.S.A.
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\authorsrightcol
GILBERT LUBCKE
3817 Patrick Henry Way
Middleton, WI 53562 U.S.A.
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DAVID B. WILLIAMS
9270-A Racquetball Way
Indianapolis, IN 46260 U.S.A.
\endauthors

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%references

Reference: 
        
Kaiser, D. H., 1994, {\it Inform. Bull. Var. Stars}, No.\,4119

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