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\begin{document}
\IBVShead{4143}{12 January 1995}

\title{Photometric observation of NS~Monocerotis}
\vspace{-1em}
\centerline{[BAV Mitteilungen Nr. 76]}

\vskip 8mm

\begintext

NS~Mon = CSV~783 = BD+7\degr 1367 (9.5) was discovered by
Hoffmeister (1934). He classified the variable as possibly Algol
type in the range between 10\fm5 and 11\fmm (pg). First
investigation of this variable was performed by Kippenhahn (1955) based on
87 plates. He found the maximum brightness not to be constant,
suspected $\beta$\ Lyr--type and gave three times of minimum light.
Three additional minima timings were submitted by Wasiljanowskaja
(1954). She supposed the variable to be of Algol type. Variability
of the star between 10\fm8 and 11\fm3 (pg) was confirmed by Weber
(1956). An investigation on 320 photographic plates by Olijnyk (1963)
resulted in
15 times of minimum light of NS Mon but the elements could
not be found. An even larger set of photographic plates was used by
H\"aussler (1978). He investigated this star on 501 plates of the
Sonneberg and Hartha Sky Patrols and derived first elements:
\begin{equation} {\rm
Min\, I = HJD}\,2441599.600 \, + \, 0\fd 9399163\times\rm E.
\end{equation}

Using the estimates on the Sonneberg plates together with the above
elements a first photographic lightcurve and an O--C diagram were
given. Unfortunately two weak stars north and south of NS Mon led to a
rather large scatter in the lightcurve. NS Mon was classified as W~UMa
type in the range between 10\fm 64 and 11\fm 08 (ph). With these above data NS Mon is listed in
the fourth edition of the GCVS (Kholopov et al. 1985).

For seventeen years the variable had remained obviously unobserved
when we put NS Mon on our program, scheduled to look after seldom
observed or in some other way problematic eclipsing binaries.

The photoelectric observations were made at the private observatory of
one of us (F.A.) with a 0.35 m automatic photoelectric telescope
(Agerer 1988). The photometer was equipped with an uncooled EMI~9781A
tube and Schott filters for B and V\@. SAO 114137 (G5) was used as
comparison star and SAO 114096 (G0) to check its constancy.

One minimum was observed photographically (P.F.)
with a Lich\-ten\-knecker Flatfield-Camera f=576mm, f/D=2.0 on hypered
KODAK Technical Pan 2415.
The exposures were evaluated with a fixed diaphragm photometer.
Altogether one new photographic and 10 photoelectric minima in two colours
could be collected. All minima times were calculated with the Kwee -- van
Woerden (1956) method.

In compiling the lightcurve (Figure 1) from our data it became evident
that the period published in the GCVS was a spurious one with the relation

\[\rm \frac{1}{P_{GCVS}} - \frac{1}{P} = \frac{1}{2}.\]

\vfill \eject

\centerline{2}
\epsfysize=90mm
\centerline{\epsffile{4143-f1.ps}}
\centerline{Figure 1: Differential light curves in B and V of NS~Mon}
\centerline{computed with respect to the new ephemeris (2).}
\epsfysize=7cm
\centerline{\epsffile{4143-f2.ps}}
\centerline{Figure 2: O--C diagram for NS~Mon computed with respect to the
 new ephemeris (2)}
\centerline{ using all available minimum timings. $\bullet$ represents  photoelectric,}
\centerline{ $\circ$ photographic series and \raisebox{0.3ex}{$_\Box$} photographic plate minima.}
\vskip 3mm
Using all published minima found in the \lq BAV Database of
Minima of Eclipsing Binaries\rq\ together with our new observations,
a weighted least squares fit yields the following linear ephemeris:

\arraycolsep0mm
\begin{equation}
  \begin{array}{r}  {\rm  Min\, I = HJD}\,2449002.4539 \\
  \pm 4 \end{array}
  \begin{array}{r}
   \, + \,\, 1\fd77761517 \\
     \pm 17 \end{array}
  \begin{array}{r}\,\times\rm\, E\\
      { }
     \end{array}
\label{1}
\end{equation}
\vskip 1mm
Our observations show the primary and secondary minima to be almost equally
deep with an amplitude of 0\fm54.  A distinction
between them was not possible. If both minima are primary ones, the
period has to be halved. As can be seen from the lightcurve, NS Mon is
in any case of the type EA.


\vfill \eject

\centerline{3}
\vskip 1mm
\centerline{Table 1}
\begin{center}
Observed times of minima for NS~Mon,
epochs and residuals computed with respect to the ephemeris (2)
derived in this paper.
\vskip 1mm
\footnotesize
\begin{tabular}{rr@{.}lrlr@{.}lr@{.}lc||rr@{.}lrlr@{.}lr@{.}lc}
\hline
 N & \multicolumn{2}{c}{JD hel.} & W & T$^*$ &
 \multicolumn{2}{c}{Epoch} &
 \multicolumn{2}{l}{O--C} & Lit &
 N & \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+} & & &
 \multicolumn{2}{c}{} &
 \multicolumn{2}{l}{} & \\
\hline
   1 & 26030 & 345 &  2 &   P   & $-$12923 & 0 &  +0 &  012  & [1] &  29 & 41330 & 330 & 20 &   F   &   $-$4316 & 0 &  +0 &  063  & [4] \\
   2 & 27100 & 452 &  2 &   P   & $-$12321 & 0 &   --0 &  005  & [1] &  30 & 41385 & 334 &  2 &   P   &   $-$4285 & 0 &   --0 &  039  & [4] \\
   3 & 27157 & 352 &  2 &   P   & $-$12289 & 0 &  +0 &  011  & [1] &  31 & 41599 & 585 &  2 &   P   &   $-$4165 & 5 &  +0 &  009  & [4] \\
   4 & 29700 & 182 &  2 &   P   & $-$10859 & 5 &   --0 &  038  & [2] &  32 & 41680 & 468 &  2 &   P   &   $-$4119 & 0 &  +0 &  011  & [4] \\
   5 & 29913 & 533 &  2 &   P   & $-$10739 & 5 &   --0 &  000  & [3] &  33 & 41983 & 569 &  2 &   P   &   $-$3949 & 5 &  +0 &  029  & [4] \\
   6 & 29913 & 559 &  2 &   P   & $-$10739 & 5 &  +0 &  026  & [3] &  34 & 42448 & 326 &  2 &   P   &   $-$3687 & 0 &   --0 &  061  & [4] \\
   7 & 30762 & 298 &  2 &   P   & $-$10261 & 0 &   --0 &  047  & [3] &  35 & 48690 & 4786& 60 &   V   &    $-$176 & 5 &   --0 &  0038 & [5] \\
   8 & 30768 & 469 &  2 &   P   & $-$10258 & 5 &   --0 &  097  & [3] &  36 & 48690 & 4805& 60 &   B   &    $-$176 & 5 &   --0 &  0019 & [5] \\
   9 & 31090 & 335 &  2 &   P   & $-$10077 & 5 &  +0 &  020  & [3] &  37 & 48985 & 5648& 60 &   V   &     $-$10 & 5 &   --0 &  0018 & [5] \\
  10 & 31531 & 184 &  2 &   P   &  $-$9829 & 5 &  +0 &  021  & [2] &  38 & 48985 & 5654& 60 &   B   &     $-$10 & 5 &   --0 &  0012 & [5] \\
  11 & 31903 & 145 &  0 &   P:: &  $-$9619 & 0 &   --0 &  429  & [2] &  39 & 48986 & 4537& 60 &   B   &      $-$9 & 0 &   --0 &  0017 & [5] \\
  12 & 34807 & 290 &  2 &   P   &  $-$7986 & 5 &   --0 &  018  & [3] &  40 & 48986 & 4541& 60 &   V   &     $-$ 9 & 0 &   --0 &  0013 & [5] \\
  13 & 34823 & 291 &  2 &   P   &  $-$7977 & 5 &   --0 &  015  & [3] &  41 & 49002 & 4527& 60 &   B   &       0 & 0 &   --0 &  0012 & [5] \\
  14 & 35135 & 285 &  2 &   P   &  $-$7801 & 0 &  +0 &  007  & [3] &  42 & 49002 & 4532& 60 &   V   &       0 & 0 &   --0 &  0007 & [5] \\
  15 & 35862 & 283 &  2 &   P   &  $-$7392 & 0 &   --0 &  040  & [3] &  43 & 49018 & 451 & 30 &   B:  &       9 & 0 &   --0 &  001  & [5] \\
  16 & 35870 & 300 &  2 &   P   &  $-$7388 & 5 &   --0 &  022  & [3] &  44 & 49018 & 454 & 30 &   V:  &       9 & 0 &  +0 &  002  & [5] \\
  17 & 36194 & 329 &  0 &   P:: &  $-$7205 & 0 &   --0 &  408  & [3] &  45 & 49059 & 3379& 60 &   B   &      32 & 0 &  +0 &  0003 & [5] \\
  18 & 36230 & 273 &  2 &   P   &  $-$7185 & 0 &   --0 &  016  & [3] &  46 & 49059 & 3380& 60 &   V   &      32 & 0 &  +0 &  0004 & [5] \\
  19 & 36278 & 301 &  2 &   P   &  $-$7158 & 0 &  +0 &  016  & [3] &  47 & 49067 & 340 & 20 &   F   &      36 & 5 &  +0 &  003  & [6] \\
  20 & 36286 & 257 &  2 &   P   &  $-$7154 & 5 &   --0 &  027  & [3] &  48 & 49370 & 419 & 30 &   V:  &     207 & 0 &   --0 &  001  & [5] \\
  21 & 36613 & 327 &  2 &   P   &  $-$6970 & 5 &   --0 &  038  & [3] &  49 & 49370 & 419 & 30 &   B:  &     207 & 0 &   --0 &  001  & [5] \\
  22 & 38673 & 614 &  2 &   P   &  $-$5811 & 5 &   --0 &  007  & [4] &  50 & 49371 & 310 & 30 &   V:  &     207 & 5 &  +0 &  001  & [5] \\
  23 & 39057 & 613 &  2 &   P   &  $-$5595 & 5 &  +0 &  027  & [4] &  51 & 49371 & 313 & 30 &   B:  &     207 & 5 &    +0 &  004  & [5] \\
  24 & 39146 & 426 &  2 &   P   &  $-$5545 & 5 &   --0 &  041  & [4] &  52 & 49402 & 420 & 30 &   V:  &     225 & 0 &  +0 &  003  & [5] \\
  25 & 39441 & 534 &  2 &   P   &  $-$5379 & 5 &   --0 &  017  & [4] &  53 & 49402 & 421 & 30 &   B:  &     225 & 0 &  +0 &  004  & [5] \\
  26 & 40152 & 585 &  2 &   P   &  $-$4979 & 5 &   --0 &  012  & [4] &  54 & 49688 & 6123& 60 &   V   &     386 & 0 &   --0 &  0011 & [5] \\
  27 & 40504 & 560 &  2 &   P   &  $-$4781 & 5 &   --0 &  005  & [4] &  55 & 49688 & 6126& 60 &   B   &     386 & 0 &   --0 &  0008 & [5] \\
  28 & 41329 & 375 & 20 &   F   &  $-$4317 & 5 &   --0 &  003  & [4] \\
\hline
\end{tabular}
\end{center}
[1]: Kippenhahn (1955),
[2]: Wasiljanowskaja (1955),
[3]: Olijnyk (1963),
[4]: H\"aussler (1978),
[5]: Agerer: this paper,
[6]: Frank: this paper.\\
$^*)$ P\, denotes pg plate min., V\, photoelectric min. in visual
and B\ in B Filter and  F\, photographic series.
Those marked with \lq :\rq\ got reduced weight while those marked with
\lq ::\rq\ were discarded.
\large

\vskip 1cm
\beginauthors
\authorsrightcol
F. AGERER
P. FRANK
Bundesdeutsche Arbeitsge\-mein\-schaft
f\"ur Ver\"anderliche Sterne e.V. (BAV)
Munsterdamm 90,
D-12169 Berlin, Germany
\endauthors

\references

 Agerer, F.: 1988, {\it BAV Rundbrief}, {\bf 37}, 60

 H\"aussler, K.: 1978, {\it Mitt. B.-H.-B\"urgel-Sternw. Hartha}, {\bf15}, 12

 Hoffmeister, C.: 1934, {\it Astr. Nachr.}, {\bf 253}, 195

 Kholopov,  P.N.~et  al.: 1985, Gen. Cat. of Var. Stars, $4^{\rm th}$\ Ed.,
     Nauka, Moscow.

 Kippenhahn, R.: 1955, {\it Astr. Nachr.}, {\bf 282}, 76

 Kwee,  K.K., van Woerden, H.: 1956, {\it Bull. Astr. Inst. Netherlands}, {\bf 12}, 327

 Olijnyk, G.T.: 1963, {\it Lvov Circ.}, {\bf 39-40}, 60

 Wasiljanowskaja, O.P.: 1955, {\it Astr. Circ.}, {\bf 157}, 19

 Weber, R.: 1956, {\it J. des Observateurs}, {\bf 39}, 113

\end{document}

