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\input ibvs2.sty

\begin{document}
\IBVShead{4910}{19 June 2000}

\IBVStitle{NSV 223: a New Eclipsing Binary}

\IBVSauth{Verrot, J.P.$^1$; Van Cauteren, P.$^2$}

\IBVSinst{Groupe Europ\'een d'Observations Stellaires (GEOS), 3 Promenade Venezia,
78000 Versailles, France,\\ \indent E-mail: jean-paul.verrot@ascom.fr}
\IBVSinst{Paul Beersel Hills Observatory,Laarheidestraat 166, B-1650
Beersel, Belgium ,\\ \indent E-mail: Paul.VanCauteren@advalvas.be}

\SIMBADobj{BD+20 0075}
\IBVStyp{ EW }
\IBVSkey{photometry}
\IBVSabs{The variability of NSV 223 was confirmed by means of visual,}
\IBVSabs{photoelectric and CCD measurements. The investigation of all available} 
\IBVSabs{minima  suggests an orbital period of 0.366128 d.}

\begintext

The rapid variability of NSV 223 (BV
121 $\equiv$ BD\,+20\deg0075 $\equiv$ CSV 005683 $\equiv$ GSC 1193972)
was discovered  by Strohmeier et al.\ (1956) and confirmed by Filatov
(1957), who reported variations from mag. 10.9 to 11.3 (photographic
plates) an a F or G spectrum.

Visual estimates carried out since 1997 by GEOS observers and mainly by
J.P.~Verrot allowed establishing a very probable eclipsing nature (and
13 times of mimimum light were detected), even though the case of a
pulsating star could not be ruled out (Verrot 1999).  Therefore,
photoelectric measurements were performed at the Jungfraujoch
Observatory, on the basis of a collaboration between GEOS and Geneva
Observatory.  Thirteen $BV$ measurements were collected in December
1998: the practically flat behaviour of the $B-V$ colour index strongly
supported the eclipsing nature.  The mean value of the $(B-V)_G$ index
is $-0.35$. The latter value can be transformed into the $BV$
system assuming a luminosity class V\@.  Unfortunately, the photometer of
the Jungfraujoch Observatory was removed before we could complete the
observation of the whole light curve.

New CCD measurements were obtained by one of us (P.~Van~Cauteren) at
his private observatory using a 0.40-m telescope.  He collected 1167
measurements in white light during 1998 using a Hisis 24 camera: these
images were reduced by using a profile fitting algorithm (MIPS package;
Buil et al.\ 1993). Moreover, he also collected  224 measurements in
$V$ light during 1999 using a ST7 camera and the MIRA Aperture
Photometry software (AP software is distributed by Axiom Research
Inc.).  In both cases GSC~1193\_523 was used as comparison star.
Typically, the standard deviation for the check star (GSC~1193\_277)
measurements is 0.012 mag. Since NSV~223 is 1.5 mag brighter, its
measurements are more precise.

From Fig.~1, it is evident that NSV 223 is a contact eclipsing
binary; it ranges from 10.86 to 11.32 in $V$ light, as determined
from Geneva photoelectric measurements. 
The light curve has a quite regular shape and the two maxima have
the same height. On the other hand, the minima are slightly different (about 0.02
mag); the noise at Min.~II can be ascribed to the  poor photometric
conditions of one night rather than to a physical variability of the
system.

An ephemeris was calculated on the basis of 15 times of minimum light
supplied by GEOS visual observers (J.P.~Verrot and J.~Vandenbroere), of
1 photoelectric time and from the 5 CCD times:
$$\begin{array}{r@{}r@{}l}
{\rm Min.~I = HJD}~2450748.896 & {} + 0\fday366128 & {} \times E. \\
{}\pm 0.003 & \pm 0.000005 \\
\end{array}$$

\IBVSfig{10cm}{4910-f1.ps}{The 224 $V$  CCD measurements of NSV~223 phased
with the ephemeris proposed below.}

A triple weight was assigned to the CCD and photoelectric minima, which
are listed in Table 1 for the sake of completeness.

\begin{table}[h]
\caption{Recent photoelectric and CCD times of minima of NSV
223}
\begin{center}
\begin{tabular}{clcl}
\hline
Type of min. & \multicolumn{1}{c}{HJD} & Method &   Filter\\
\hline
II   & 51124.3492 & CCD &  white light  \\
II   & 51128.3899 & CCD &  white light   \\
I   &  51166.2751 & p.e. & $V$ light \\
II   & 51467.4273 & CCD & $V$ light  \\
I  & 51468.3428 & CCD &   $V$ light \\
I  & 51469.4389 & CCD & $V$ light \\
\hline
\end{tabular}
\end{center}
\end{table}

P. Van Cauteren is grateful to the Royal Observatory of Belgium for
putting at his disposal material acquired by project G.0265.97 of the
Fund for Scientific Research (FWO) --- Flanders (Belgium); sincere thanks
to Dr.~Jan Cuypers.

\references

Buil, C., Klotz, A. et al., 1993, Manual for the Microcomputer Image
Processing System V2.0

Filatov, G.S., 1957, Astron.\ Tzirk., 182

Strohmeier, W., Kippenhahn, R., Geyer E.,  1956, KVB, 15 

Verrot, J.P., 1999, NC~GEOS, 902
\end{document}

