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\IBVShead{4557}{16 February 1998}

\IBVStitle{HIP 12056 IS AN ECLIPSING BINARY SYSTEM}

\IBVSauth{J. VIDAL-SAINZ}

\IBVSinsto{Grup d'Estudis Astronomics, Apartado 9481, 08080 Barcelona, Spain}
\IBVSinsto{e-mail: vidal@astro.gea.cesca.es}

\SIMBADobj{HIP 12056}

\begintext

HIP\,12056 (SAO\,38145 = PPM\,45234 = HD\,15965 = BD\,+45\deg 628 = AGK +45\deg 0275 
= GSC\,3295.2164) was observed by the  HIPPARCOS satellite and found variable, 
and it was listed among the unsolved variable stars (ESA, 1997). According 
to the HD catalogue, this object is an A star, while it is listed as a B8 type
star in the PPM.
 
The analysis of the HIPPARCOS photometric  data showed that HIP 12056 is 
actually an eclipsing binary system with a period over two days and a maximum 
V magnitude of 9.19 $\pm$0.01 (Figure 1). To obtain more information about it, 
the star was monitored in the V band, from 21 August to 14 December 1997, 
at Monegrillo Observatory using the 0.4-m Newtonian  telescope. SAO 38137 was 
used as comparison star, with V=8\fmm 235 as calculated from Tycho magnitudes.

Observations show that HIP 12056 is an eclipsing binary system with a 
period close to 2.165 days. Figure 2 depicts the folded light curve. At
primary minimum, the star fades by 0.18 magnitudes. The secondary minimum is 
0.16 magnitude deep. HIPPARCOS data provided a primary minimum that was 
taken as zero epoch. The final derived ephemeris is the following:

\vskip 1mm
\centerline{Min. I = HJD 2448430.0254 + 2\fday 165016 $\times$ E}
\hspace*{70mm} $\pm$0.0040   $\pm$0.000010
\vskip 2mm

The combined set of satellite data and CCD observations allowed to compute the
time of eight minima, using  Kwee and van Woerden's (1956) method, and the
respective O$-$C residuals, all of them summarized in Table 1.
\vskip 2mm
\centerline{Table 1}
\vskip 1mm
\begin{center}
\begin{tabular}{crc}
\hline
                 HJD +2400000  &    Epoch  &  O$-$C\\
\hline
                 48430.0060   &      0.0 &   $-$0.0195\\
                 48431.1221   &      0.5 &   +0.0142\\       
                 48433.2533   &      1.5 &   $-$0.0196\\
                 48617.2801   &     86.5 &   $-$0.0192\\
                 50718.4493   &   1057.0 &   +0.0020 \\
                 50731.4443   &   1063.0 &   +0.0069\\
                 50795.3130   &   1092.5 &   +0.0076\\
                 50796.3950   &   1093.0 &   +0.0071\\      
\hline
\end{tabular}
\end{center}
\newpage

\IBVSfig{9cm}{4557-f1.ps}{Light curve of HIP\,12056 derived from the original satellite data folded according to the given ephemeris}
\vskip -1.8cm

\IBVSfig{9cm}{4557-f2.ps}{Photometric observations of HIP 12056 phased according to the given ephemeris}

\vskip 3mm

\references

ESA, 1997, The Hipparcos and Tycho Catalogs, ESA SP-1200

Kwee, K.K. and van Woerden, H., 1956, {\it BAN}, {\bf 12}, 327

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