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\IBVShead{4320}{10 April 1996}

\centerline{\ft NEW INFORMATION ON V\,558 Cas: TYPE AND PERIOD}
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\begintext

New photoelectric measurements show that V558 Cas is likely  an
EB-type  eclipsing binary varying from magnitude 8.70 (V) to 8.91 (V) with
a period of approximately 3.16 days. The variability of V558 Cas =
HD\,12762 was discovered by Strohmeier et al. (1962)
using the photographic plates from Bamberg.  The
star was mentioned as an eclipsing star of magnitude 8.1 (p) with an
amplitude of 0\fm 6 and A-type spectrum.  In 1969 and 1970, at the
Lund observatory,  Bern et al. (1971) measured the star
photoelectrically. They catalogued it ranging from 8\fm 7 to 8\fm 9 in V
with B$-$V colour index of 0.72 and U$-$B colour index of 0.21.  They
simply confirmed the variability of the star.  In the GCVS
(Kholopov et al., 1985), V558 Cas is listed as an eclipsing star (E)
varying from 9.0 to 9.6 (B) with an A to F spectrum. 

32 new photoelectric measurements of V558 Cas (see Table 1) were obtained
during several GEOS missions, at the Jungfraujoch station, with the
photometer equipped with filters of the Geneva system, attached to
the 76-cm telescope.  These measurements were carried out from
December 1992 to August 1995.  These data confirm the results published by
Bern et al. (1971): the star varies from 8.70 to 8.91 in V with
almost constant B$-$V colour index of 0.70. 

Period search was performed using four different
methods.  The theta statistic function of Renson (1978) gave the
best results due to the limited set of measurements, the low
amplitude and the shape of the light curve. 

For the light curve 
(Figure 1), the epoch was chosen close to the instant of dimmest magnitude
and adjusted using a spline function:
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\centerline{Min\,I = HJD\,2448978.706 + 3.1605 $\times$ E}


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\centerline{Figure 1. Folded light curve with 32 measurements in 
V of V558 Cas}
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\centerline{2}
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\centerline{Table 1. New photoelectric measurements of V558 Cas}
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\begin{tabular}{ccc}
\hline
HJD\,(2400000+)&V&(B$-$V)$_G$\\
\hline
\\
48620.2904&8.775&$-$0.110\\
48620.3390&8.776&$-$0.099\\
48621.2834&8.815&$-$0.113\\
48621.3320&8.839&$-$0.112\\
48621.3494&8.839&$-$0.119\\
48621.3834&8.849&$-$0.113\\
48622.3104&8.705&$-$0.117\\
48622.3438&8.701&$-$0.122\\
48623.3673&8.833&$-$0.126\\
48623.3916&8.833&$-$0.115\\
48624.2652&8.751&$-$0.118\\
48624.2819&8.753&$-$0.116\\
48624.3305&8.777&$-$0.121\\
48978.4178&8.811&$-$0.114\\
48978.6400&8.905&$-$0.096\\
48981.3038&8.745&$-$0.126\\
48981.5093&8.789&$-$0.106\\
48981.5697&8.808&$-$0.095\\
48981.6496&8.838&$-$0.071\\
48982.3135&8.780&$-$0.118\\
48982.3989&8.760&$-$0.120\\
48982.5509&8.714&$-$0.102\\
48982.6086&8.703&$-$0.092\\
48983.3051&8.872&$-$0.128\\
49721.5158&8.897&$-$0.113\\
49721.6082&8.837&$-$0.091\\
49722.2950&8.723&$-$0.126\\
49807.3544&8.712&$-$0.096\\
49810.3442&8.806&$-$0.096\\
49811.3337&8.856&$-$0.119\\
49950.5604&8.860&$-$0.119\\
49950.5680&8.856&$-$0.111\\
\hline
\end{tabular}
\end{center}
\large
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with primary minimum at 8.91 (V) and secondary one at 8.87 (V), the
shape of the light curve looks like the EB type. 

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\beginauthors
\authorsrightcol
Jacqueline VANDENBROERE 
GEOS (Groupe Europ\'een 
d'Observations Stellaires) 
Promenade V\'en\'ezia, 3 
F 78000 Versailles, France
\endauthors
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\references

Bern, K. and Virdefors, B., 1972, {\it Astron. Astrophys. Suppl.
S.}, {\bf 6}, 117 

Renson, P., 1978, {\it Astron. Astrophys.}, {\bf 63}, 125

Strohmeier, W., Knigge, R. and Ott, H., 1962, {\it Ver\"off. der
Remeis-Sternwarte Bamberg}, V, 14 

Kholopov, P.N. et al., 1985, General Catalogue of Variable Stars,
 Fourth edition, Moscow

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