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\IBVShead{4639}{12 October 1998}

\IBVStitle{TWO LONG-NEGLECTED INTERESTING ECLIPSING BINARIES}

\IBVSauth{Nikolai Samus$^1$, Felicia Tam$^2$}
\IBVSinst{Institute of Astronomy, Russian Academy of Sciences,
48, Pyatnitskaya Str., Moscow 109017, Russia; visiting astronomer,
Maria Mitchell Observatory, Nantucket, MA 02554, USA
[samus@sai.msu.su]} %email

\IBVSinst{Department of Physics, Stanford University, Stanford, CA 94305, USA and Maria Mitchell Observatory,
Nantucket, MA 02554, USA
[ftam@leland.stanford.edu]} %email


\IBVSabs{Two eclipsing binaries have been studied photographically.}

\SIMBADobj{V936 Aql, VX Sct}
\IBVStyp{ E }
\IBVSkey{photometry, photographic}

\begintext

In the course of studying variable stars lacking
finding charts or having other identification problems, we have studied
two rather interesting eclipsing binaries, VX Sct and V936 Aql.

VX Sct was discovered by Cannon (1924). Oosterhoff (1943) found that
it was an Algol star varying between $13\fmm 6$ and $14\fmm 2$ (photographic
magnitudes) and having the following light elements:
\begin{equation}
{\rm Min} = \hbox{JD}2427926.8 + 33\fday 623\times E.
\end{equation}
To our knowledge, no finding chart is available in the literature. Despite
that, Szafraniec (1963) published a number of visual observations obtained
by several observers and Kreiner (1976) published one uncertain date of
minimum.

Using plates of the Maria Mitchell Observatory archive, we have rediscovered
and studied the star. It is identical to GSC 5699.5176 ($18\hr 33\mm 59\fsec 64$,
$-11\deg 54'57\farcs 5$, 2000.0). Improved light elements have been
determined:
\begin{equation}
{\rm Min}= \hbox{JD}2447359.4+33\fday 6208\times E.
\end{equation}

Table 1 presents the list of minima from the literature and of
definite fadings from our
observations, with $(O-C)$ values from the elements (2).

The system is interesting because it probably has giant components and
deserves further study.

V936 Aql was discovered by Harwood (1962) and never observed since.
Harwood announced the star to be a short-period eclipser varying between
$13\fmm 9$ and $14\fmm 8$ (photographic magnitudes). In the position shown
by Harwood's finding chart, two stars are present in the US Naval
Observatory A1.0 catalog: $19\hr 0\mm 17\fsec 48$, $-5\deg 37'50\farcs 0$
($m_{blue}=14\fmm 5$, $m_{red}=12\fmm 6$) and $19\hr 0\mm 17\fsec16$,
$-5\deg 37'57\farcs 1$ ($m_{blue}=14\fmm 4$, $m_{red}=11\fmm 7$).
The first of the two stars is identical to GSC 5140.2463
($19\hr 0\mm17\fsec 48$, $-5\deg 37'49\farcs 0$, 2000.0).

\begin{table}[p]
\caption{Minima of VX Sct}
\begin{center}
\begin{tabular}{lrllrl}
\hline
JD 24\dots & $O-C$ & Source & JD 24\dots & $O-C$ & Source\\
\hline
23588.6  &--0\fday9 &Oosterhoff        &  33507.7 & +0\fday1& Present paper\\
23993.6  & +0.7 &Oosterhoff        &  33541.6 & +0.3& Present paper\\
25305.65:& +1.5:&Kreiner           &  33910.5 &--0.6& Present paper\\
27926.9  & +0.3 &Oosterhoff        &  34213.7 &  0.0& Present paper\\
27960.9  & +0.7 &Oosterhoff        &  34650.5 &--0.2& Present paper\\
29104.4  & +1.1 &Oosterhoff        &  34651.5 & +0.8& Present paper\\
29136.4  &--0.5 &Oosterhoff        &  39761.6 & +0.5& Present paper\\
29439.5  &  0.0 &Oosterhoff        &  44434.8 & +0.4& Present paper\\
32464.5  &--0.9 &Present paper     &  45611.5 & +0.4& Present paper\\
32800.6  &--1.0 &Present paper     &  46619.7 &  0.0& Present paper\\
32801.6  &  0.0 &Present paper     &  47358.7 &--0.7& Present paper\\
33506.7  &--0.9 &Present paper     &  47393.7 & +0.7& Present paper\\
\hline
\end{tabular}
\end{center}
\vskip8mm
\caption{Minima of V936 Aql}
\begin{center}
\begin{tabular}{lrllrl}
\hline
JDhel 24\dots & $O-C$ & Source & JDhel 24\dots & $O-C$ & Source\\
\hline
24382.396      & +0\fday008  &MMO& 34602.824 & +0\fday008 & MMO \\
25407.697      &    --0.012  &MMO&     35753.885          &--0.004 & MMO    \\
26217.667:     &     +0.012: &MMO&     38964.265          &  0.000 & Moscow \\
26513.490      &    --0.004  &MMO&     40065.221          &--0.005 & Moscow \\
26942.745:     &    --0.054: &MMO&     40808.196          & +0.002 & Moscow \\
27284.409      &    --0.003  &MMO&     41188.348          &--0.002 & Moscow \\
27669.396      &     +0.007  &MMO&     41219.667          &--0.002 & MMO    \\
27988.831      &    --0.006  &MMO&     41521.285          &--0.003 & Moscow \\
28370.436      &    --0.005  &MMO&     42547.565          &--0.001 & Moscow \\
28716.872      &      0.000  &MMO&     42978.788:         &--0.007:& MMO    \\
29051.779:     &     +0.039: &MMO&     43746.826:         & +0.009:& MMO    \\
29468.527      &     +0.011  &MMO&     44102.390          &--0.010 & MMO    \\
29845.788      &     +0.004  &MMO&     44460.869          &--0.006 & MMO    \\
32433.659:     &     +0.006: &MMO&     44816.463          & +0.006 & MMO    \\
32762.737      &     -0.001  &MMO&     45519.428          &--0.005 & MMO    \\
33121.706      &     +0.011  &MMO&     46319.738          & +0.002 & MMO    \\
33481.619      &     +0.003  &MMO&     47802.778          & +0.002 & MMO    \\
33853.578      &    --0.005  &MMO&     48090.430          & +0.007 & Moscow \\
\hline
\end{tabular}
\end{center}
\end{table}


We estimated V936 Aql on 1167 plates of the MMO collection (7.5-inch
Cooke refractor at Nantucket) and on
249 plates of the Moscow archive (40-cm astrograph, first
in Kuchino near Moscow, then at the Crimean Laboratory of the
Sternberg Astronomical Institute). The plates span the JD interval
from 2421871 to 2448397.
The photographs show that it is the north-western (GSC) star that really
varies.
The red companion is almost always considerably fainter than the
variable. On MMO plates, the images of the two stars merge on many
plates, thus making estimates difficult. On Moscow plates, both stars
are usually distinctly visible separately.

From our observations, the star is an eclipsing variable, either of
Algol type with non-spherical components or even of $\beta$ Lyr type,
with the period as short as $0\fday 48$, more characteristic of EW stars
or cataclysmic systems. Moscow plates show variations
between $14\fmm 0$ and $15\fmm 0B$. The secondary minimum, though not
deep, is clearly present.
The mean light curve from Moscow plates is shown in Figure 1.
Dates of minima derived from seasonal light curves are collected in
Table 2. The star definitely shows period variations, apparently
not abrupt but continuous (see Figure~2). The elements
\begin{equation}
\begin{array}{r@{}r@{}r@{}l}
\hbox{Min(hel)} = 2424382.388 &  {} + 0\fday 48182392& {}\times E - 4\fday 6 & {}\times 10^{-11} \times E^2 \\
{} \pm0.003 & {} \pm0.00000032 & {} \pm0.6
\end{array}
\end{equation}
represent the observations quite satisfactory; $(O-C)$ values
from elements (3) are presented in the last column of Table 2.

CCD observations of V936 Aql are highly desirable.

\IBVSfig{10cm}{4639-f1.ps}{The mean light curve of V936 Aql from Moscow plates}

\vfill\eject

\IBVSfig{10cm}{4639-f2.ps}{The $O-C$ plot for V936 Aql. The $O-C$ values are from the
preliminary linear light elements ${\rm Min} = {\rm JD\ } 2441521.285 + 0\fday481821\times E$.
Open circles, uncertain values. The curve is the parabola corresponding
to Eq.\ (3).}

\references

Cannon, A.J. 1927, Harvard Obs.\ Circ.\ No.\,265

Harwood, M. 1962, Leiden Obs.\ Ann.\ 21, 387

Kreiner, J.M. 1976, Acta Astron.\ 26, 341

Oosterhoff, P.Th. 1943, BAN 9, 399

Szafraniec, R. 1963, Acta Astron.\ Suppl.\ 6

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