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\IBVShead{4481}{26 May 1997}
\title{New Elements of V694~Aquilae}
\vspace{-3em}
\centerline{[BAV Mitteilungen Nr. 97]}
\vskip 8mm

\begintext

V694~Aql = 92.1940~Aql = GSC~1058.32 was discovered by Hoffmeister (1940)
on photographic plates of the Sonneberg Observatory. He classified the
star as an Algol-type variable in the range between 12\fm 0 and 12\fm 5. 

First investigation of this variable was performed by Rohlfs (1949).
She published 25 minima (times for plates with weak images), a
photographic normal light-curve and first elements:
\begin{equation} {\rm Min\,\, I = HJD\quad} 
     2428782.334 \, + \, 0\fd450175\times\rm E
\end{equation}
The range of brightness is given as 12\fm 4 - 12\fm 9 (phot.).
From her measurements she derived a time of constant light in the
minimum of 1\fh 4. With these data V694 Aql is listed in
the fourth edition of the GCVS (Kholopov et al.~1985).

Popper (1956) and Wood (1963) pointed out that V694 Aql is of special
interest because of its, for an Algol type variable, extreme short
period of 0\fd 45.  Popper gives for the primary component a radius of $\rm 0.3 R_\odot$, spectral class F0 and the radial velocities from two spectrograms.
Based on the period given by Rohlfs, Brancewicz and Dworak (1980)
published additional geometrical and physical parameters.

Almost 50 years later we put V694 Aql on our observing program. The
CCD observations were made with SBIG ST6 cameras without filters,
attached to a 32cm RC telescope with f = 1740 mm (WM), a 20cm SC
telescope with f= 1200 mm (WK) and a 10cm Aero-Ektar astrograph with f
= 600 mm (PF). The integration times were 60 seconds at the RC/SC--telescopes 
and 90 seconds at the astrograph. Our CCD observations
cover 3 years. GSC 1058.1442 served as the comparison star and several other
stars in the same field were used to check its constancy. In our
instrumental system (Aero Ektar) the amplitude of variability is 0\fm
50 for the primary minima and 0\fm 15 for the secondary minima. A
constant phase in minimum light could not be detected. All our CCD
measured times of minimum light were calculated with the Kwee and van
Woerden (1956) method. A thorough study of our
measurements showed that the period given in the GCVS is a spurious
one with the relation:
\begin{equation}
\rm\frac{1}{P_{GCVS}} - \frac{1}{P} = \frac{1}{1d_{sid}}
\end{equation}
Using only CCD measured minima a weighted least squares fit led to the
new ephemeris:
\begin{equation}
  \begin{array}{r}  {\rm  Min\,\,  I = HJD\quad}  2450281.5621\\
  \pm 2\end{array}
  \begin{array}{r}
   + \,\,\,\, 0\fdd \hspace{-1ex}.\,8205762\\
     \pm 5\end{array}
  \begin{array}{l}\hspace{-1ex}\times \rm\,\,E\\
      { }
     \end{array}
\label{1}
\end{equation}
\vfill \eject

\centerline{2}
\vskip 1mm

One of us (WM) investigated the variable on about 300 photographic
plates of the 0.4m astrographs of the Sonneberg Observatory. 12
additional times of minimum light of V694~Aql could be found. The
plates taken between JD 2442000 and JD 2448000 were of first quality.
The scatter of the results is therefore small. The gap between JD
2432000 and JD 2442000 could not be closed due to a lack of useful plates
from that time.
Using all available minima a weighted least squares fit led to the
new ephemeris:
\begin{equation}
  \begin{array}{r}  {\rm  Min\,\,  I = HJD\quad}  2450281.563 \\
  \pm 4\end{array}
  \begin{array}{r}
   + \,\,\,\, 0\fdd \hspace{-1ex}.\,8205795\\
     \pm 4\end{array}
  \begin{array}{l}\hspace{-1ex}\times\rm\,\,E\\
      { }
     \end{array}
\label{2}
\end{equation}
\epsfysize=8cm
\centerline{\epsffile{4481-f1.ps}}
\begin{center}
Figure 1. Differential light curve of V694~Aql
(Aero-Ektar 100/610 mm) drawn with the new
ephemeris (\ref{1})
\end{center}
\epsfysize=8cm
\centerline{\epsffile{4481-f2.ps}}
\begin{center}
Figure 2 O$-$C diagram for V694~Aql using the new
ephemeris (\ref{1}) (dots) and the ephemeris (\ref{2}) (dashes). $\bullet$\  represent CCD measured minima and
$\Box$\  minima on photographic plates
\end{center}

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\centerline{3}
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\begin{center}
Table 1. Observed times of minima for V694 Aql, epochs and residuals
 computed with respect to the linear ephemeris (\ref{1}) derived in this paper.
\footnotesize
\vskip 2mm
\vspace{1ex}
\begin{tabular}{r@{.}lrlr@{.}lr@{.}lc||r@{.}lrlr@{.}lr@{.}lc}
\hline
  \multicolumn{2}{c}{JD hel.} & W & T$^*$ &
 \multicolumn{2}{c}{Epoch} &
 \multicolumn{2}{l}{O$-$C} & Lit &
  \multicolumn{2}{c}{JD hel.} & W & T$^*$ &
 \multicolumn{2}{c}{Epoch} &
 \multicolumn{2}{l}{O$-$C} & Lit \\
  \multicolumn{2}{c}{2400000+} & & &
 \multicolumn{2}{c}{} &
 \multicolumn{2}{l}{} & &
  \multicolumn{2}{c}{2400000+}\\
\hline
28782 & 357 & 1 & P &$ -26200$& 0 &$ -0$& 109 & [1]& 31352 & 341 &  1 & P &$ -23068$& 0 &$ -0$&  169  & [1] \\
28809 & 332 & 1 & P &$ -26168$& 5 &$ +0$& 198 & [1]& 42630 & 469 &  1 & P &$  -9324$& 0 &$ -0$&  041  & [2] \\
29106 & 436 & 1 & P &$ -25805$& 0 &$ -0$& 157 & [1]& 43019 & 394 &  1 & P &$  -8850$& 0 &$ -0$&  069  & [2] \\
29111 & 422 & 1 & P &$ -25799$& 0 &$ -0$& 095 & [1]& 45493 & 483 &  1 & P &$  -5835$& 0 &$ -0$&  017  & [2] \\
29166 & 320 & 1 & P &$ -25732$& 0 &$ -0$& 175 & [1]& 45854 & 543 &  1 & P &$  -5395$& 0 &$ -0$&  011  & [2] \\
29463 & 448 & 1 & P &$ -25370$& 0 &$ -0$& 096 & [1]& 45905 & 423 &  1 & P &$  -5333$& 0 &$ -0$&  006  & [2] \\
29546 & 281 & 1 & P &$ -25269$& 0 &$ -0$& 141 & [1]& 46271 & 407 &  1 & P &$  -4887$& 0 &$ +0$&  001  & [2] \\
29783 & 476 & 1 & P &$ -24980$& 0 &$ -0$& 093 & [1]& 46289 & 432 &  1 & P &$  -4865$& 0 &$ -0$&  027  & [2] \\
29824 & 513 & 1 & P &$ -24930$& 0 &$ -0$& 084 & [1]& 46354 & 279 &  1 & P &$  -4786$& 0 &$ -0$&  005  & [2] \\
29879 & 443 & 1 & P &$ -24863$& 0 &$ -0$& 133 & [1]& 47438 & 265 &  1 & P &$  -3465$& 0 &$ -0$&  001  & [2] \\
30199 & 445 & 1 & P &$ -24473$& 0 &$ -0$& 156 & [1]& 47822 & 297 &  1 & P &$  -2997$& 0 &$ +0$&  002  & [2] \\
30446 & 623 & 1 & P &$ -24172$& 0 &$ +0$& 029 & [1]& 47859 & 218 &  1 & P &$  -2952$& 0 &$ -0$&  003  & [2] \\
30496 & 510 & 1 & P &$ -24111$& 0 &$ -0$& 139 & [1]& 49168 & 4495& 10 & E &$  -1357$& 5 &$ -0$&  0010 & [2] \\
30547 & 475 & 1 & P &$ -24049$& 0 &$ -0$& 050 & [1]& 49250 & 51  &  5 & E:&$  -1257$& 5 &$ +0$&  00   & [2] \\
30904 & 469 & 1 & P &$ -23614$& 0 &$ -0$& 007 & [1]& 50279 & 5170& 10 & E &$     -3$& 5 &$ +0$&  0063 & [3] \\
30931 & 445 & 1 & P &$ -23581$& 0 &$ -0$& 110 & [1]& 50281 & 5613& 10 & E &$      0$& 0 &$ -0$&  0008 & [4] \\
30940 & 430 & 1 & P &$ -23570$& 0 &$ -0$& 151 & [1]& 50284 & 4323& 10 & E &$      3$& 5 &$ -0$&  0018 & [3] \\
31028 & 283 & 1 & P &$ -23463$& 0 &$ -0$& 100 & [1]& 50286 & 4844& 10 & E &$      6$& 0 &$ -0$&  0012 & [4] \\
31229 & 510 & 1 & P &$ -23218$& 0 &$ +0$& 086 & [1]& 50300 & 4350& 10 & E &$     23$& 0 &$ -0$&  0004 & [5] \\
31238 & 495 & 1 & P &$ -23207$& 0 &$ +0$& 045 & [1]& 50314 & 3843& 10 & E &$     40$& 0 &$ -0$&  0008 & [3] \\
31292 & 468 & 1 & P &$ -23141$& 0 &$ -0$& 140 & [1]& 50332 & 4376& 10 & E &$     62$& 0 &$ -0$&  0002 & [2] \\
31324 & 506 & 1 & P &$ -23102$& 0 &$ -0$& 105 & [1]& 50360 & 3369& 10 & E &$     96$& 0 &$ -0$&  0005 & [2] \\
31325 & 400 & 1 & P &$ -23101$& 0 &$ -0$& 031 & [1]& 50381 & 2612& 10 & E &$    121$& 5 &$ -0$&  0009 & [5] \\
31343 & 366 & 1 & P &$ -23079$& 0 &$ -0$& 118 & [1]& 50383 & 3138& 10 & E &$    124$& 0 &$ +0$&  0003 & [2] \\
 \hline\\
 \multicolumn{16}{l}{\normalsize $^*)$ P\, denotes photographic minima and 
  E\, CCD observed minima.}\\
 \multicolumn{13}{l}{\normalsize~~~Those marked with \lq :\rq\  got reduced 
weight.}\\
\end{tabular}
\end{center}
\vskip 3mm
[1]: E.~Rohlfs: VSS 1.236,
[2]: W.~Moschner: this paper,
[3]: P.~Frank: this paper,\newline
[4]: P.~Frank \& W.~Moschner: this paper,
[5]: W.~Kleikamp: this paper
\vskip 5mm

We want to acknowledge the help and assistance by the management and
staff of Sonneberg Observatory, especially of Dr. Peter Kroll in using
the library and plate archive.

\vskip 14mm
\beginauthors
\authorsrightcol
 P.~FRANK
 W.~KLEIKAMP
 W.~MOSCHNER
 Bundesdeutsche Arbeitsgemeinschaft
 f\"{u}r Ver\"anderliche Sterne e.V. 
 (BAV)
 Munsterdamm 90,
 D-12169 Berlin, Germany
\vskip 3mm
E-mail:
wilhelm.kleikamp@t-online.de                     %email

wolfgang.moschner@t-online.de                    %email

frank.velden@t-online.de                    %email

\endauthors
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\centerline{4}
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\references

Brancewicz, H.~K., Dworak, T.~Z., 1980, {\it Acta Astronomica,} {\bf 30},
501

Hoffmeister, C., 1940, {\it Erg. AN},  {\bf 10,} 2

Kholopov, P.~N.~et al.,~1985, {\it General Catalogue of Variable Stars,}
4th Edition, Nauka, Moscow

Kwee, K.~K., van Woerden, H., 1956, {\it Bull.~Astr.~Inst.~Netherlands}, {\bf 12}, 32

Popper, D. M., 1956, {\it Publ.~Astron.~Soc.~Pac.}, {\bf 68}, 131

Rohlfs, E., 1949, {\it Ver\"{o}ffentlichungen der Sternwarte zu Sonneberg}
{\bf 1}, No.\,3

Wood et al.,~1963, {\it Flower Reprint}, No.\,140

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