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\IBVShead{5486}{9 December 2003}

\IBVStitletl{The First Complete CCD Light Curves}{ and Orbital Period Change of IK P\lowercase{er}}

\IBVSauth{Zhu, Liying$^{1,2}$; Qian, Shengbang$^{1,2}$; Xiang, Fuyuan$^3$}

\IBVSinst{National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, P. O. Box 110, 650011 Kunming, P. R. China; e-mail: lyzhu16@hotmail.com}

\IBVSinst{United Laboratory of Optical Astronomy, Chinese Academy of Sciences (ULOAC), 100012 Beijing, P. R. China}

\IBVSinst{Physics Department, Xiangtan University, 411105 Xiangtan, Hunan Province, P. R. China}

\SIMBADobj{IK Per}

\begintext

\vspace*{-0.7cm}

According to the 4th edition of the General Catalogue of Variable Stars
(GCVS) (Kholopov et al., 1987), IK Per is a short-period eclipsing binary
system with a period of $P=0\fday67603467$ and belongs to EB/KE type.
Although some visual, photographic and photoelectric times of light minimum
have been published, it was a neglected system for study. Up to now, no
complete photoelectric and CCD light curves were obtained. For understanding
the properties of light variation and studying the period change of the
system, we choose it as our object to observe.

Observations of the eclipsing binary system IK Per in B and V bands were
carried out on December 2, 3, and 4, 2002, with the PI1024 TKB CCD
photometric system attached to the 1.0-meter Cassegrain reflector telescope
at the Yunnan Observatory in P. R. China. The field of view of the CCD image
at the Cassegrain focus is $6.5\times6.5$ square arc minutes. The B and V
filters used approximate the standard Johnson UBV photometric system. During
the observations, the integration time for each image was 120 seconds. A total
of 273 images in V and 273 images in B were obtained. Image reductions were
done by using IRAF packages. One of the CCD images is displayed in Figure 1.

\vspace*{-0.5cm}

\begin{table}[!hb]
\caption{The coordinates of the variable, comparison star and check star}
\begin{center}
\begin{tabular} {llll}
\hline\hline
Stars              &year     & $\alpha$        & $\delta$
\\\hline\hline
Variable (star 1)  & 2000    & 04:29:27.46   & 42:03:10.7  \\
Comparison (star 2)& 2000    & 04:29:26.53   & 41:58:53.1  \\
Check(star 3)      & 2000    & 04:29:02.4    &42:01:12.4
\\\hline\hline
\end{tabular}
\end{center}
\end{table}

\vspace*{-0.3cm}

The observations obtained in the three days are plotted in Figure 2, where
the phases were calculated with a new period of $0\fday67602324$ (Eq. 4).
The light curves appear to exhibit a typical O'Connell effect, with
Maximum I being 0.015 mag.(V) and 0.020 mag.(B) fainter than Maximum II.
The light variation is continuous with a slightly large difference
between the depths of the two minima. The secondary minimum is about
0.07~mag.(V) and 0.08 mag. (B) brighter than the primary minimum.
With the observed data, one primary and two secondary times of light minimum
are obtained by means of parabola fitting. The new determined times of light
minimum and several recently published photoelectric minima times are given in
Table 2.

\IBVSfig{8cm}{5486-f1.eps}{CCD image of IK Per, comparison and check stars.}

%%\IBVSfigKey{5486-f1.eps}{IK Per}{finding chart}

The early times of light minimum for IK Per were compiled by Kreiner
et al. (2000), which were kindly provided by Prof. Kim Chun-Hwey. The
O--C curve calculated with the ephemeris given by Kreiner et al.,
\begin{equation}
{\rm Min.I=HJD} 2427397.534+0\fday67603467\times{\rm E},
\end{equation}
\noindent
is shown in Figure 3 where solid dots refer to photoelectric or CCD (PEC)
observations, and open circles to visual or photographic (VP) data. As
displayed in the figure, although O--C values of the VP observations show
a slightly large scatter (up to $0\fday03$), the general O--C trend
reveals that the period of IK Per is variable.

Since no data is available between E=17348.5 and 31962.5,
the properties of the period change are not clear. By assuming a long-term
period decrease, a weighted least-squares solution with weights 10 to
PEC data and 1 to VP observations yields the following ephemeris,
\begin{equation}
{\rm Min.I=HJD} 2427397.4934(51)+0\fday67604353(3)\times{\rm E} 
-2.48(1)\times{10^{-10}}\times{E^{2}}.
\end{equation}
\noindent
With the quadratic term in the ephemeris, a secular period decrease rate of\\
\hbox{${\rm d}P/{\rm d}t=-2.68\times{10^{-7}}$\,days/year} is derived. On the other hand,
the period change may not vary continuously. With the data before E=17348.5,
the linear ephemeris,
\begin{equation}
{\rm Min.I=HJD} 2427397.5190(93)+0\fday67603280(108)\times{\rm E},
\end{equation}
\noindent
is determined by a least-squares solution. For the observations after
E=17348.5, the ephemeris
\begin{equation}
{\rm Min.I=HJD} 2427397.8995(149)+0\fday67602324(42)\times{\rm E},
\end{equation}
\noindent
is derived, which can be used to predict the epochs of light minimum.
The 
$(O-C)^{\prime}$ values of all the PEC times respect to this ephemeris are
also listed in table 2.
The two linear ephemeris reveal that a sudden period decrease,
$\Delta{P}=1.329\times{10^{-5}}$\,days=1.15\,s, might occur around E=28000.
In order to check the period variation of the system, more
times of light minimum are required.


\clearpage

\IBVSfig{8cm}{5486-f2.eps}{CCD light curves in V and B for IK Per, where the phases were calculated with the period ($p=0\fday67602324$) given in the new linear ephemeris.\vspace*{-1.9cm}}

\IBVSfig{8cm}{5486-f3.eps}{O-C plot in days for IK Per. Circles refers to the VP observations and solid dots to the PEC data. Also given in solid line is the quadratic fit.}

%%\IBVSfigKey{5486-f2.eps}{IK Per}{light curve}
%%\IBVSfigKey{5486-f3.eps}{IK Per}{O-C diagram}


This work was supported by Yunnan Natural Science Foundation (No. 2001A0026Q
and No. 2003A0072M),
the Chinese Natural Science Foundation (No.10003004), and by the National
Key Fundamental Research Project (No. G1999075405). We thank Prof. Kim, C.-H.
who sent us the times of light minimum compiled by Kreiner et al. (2000).


\newpage

\begin{table}[!ht]
\normalsize
\caption{CCD and photoelectric times of light minimum for IK Per.}
\begin{center}
\begin{tabular}{lllllllll}
\hline\hline
JD (Hel.) & Error&Min.&Meth&Filter&E&$O-C$& $(O-C)^{\prime}$ & Ref.\\
+2400000  &&&&&&&&\\
\hline\hline
49005.2917& $\pm0.0015$ &II &pe  &BV &31962.5 &$-$0.0005 &$-$0.0006 & (1)\\
49310.5163& $\pm0.0016$ &I  &pe  &BV &32414   &$-$0.0056 &$-$0.0005 & (2)\\
51249.3580& $\pm0.0012$ &I  &pe  &   &35282   &$-$0.0312 &+0.0065 & (3)\\
51470.4169& $\pm0.0070$ &I  &pe  &   &35609   &$-$0.0357 &+0.0058 & (4)\\
52611.1995& $\pm0.0009$ &II &CCD &BV &37296.5 &$-$0.0616 &$-$0.0008 & (5)\\
52612.2164& $\pm0.0004$ &I  &CCD &BV &37298   &$-$0.0587 &+0.0021 & (5)\\
52613.2250& $\pm0.0007$ &II &CCD &BV &37299.5 &$-$0.0642 &$-$0.0033 & (5)\\
\hline\hline
\end{tabular}
\end{center}
{References in Table 2: (1) Huebscher et al.(1993); (2) Huebscher et al.
(1994); (3) Agerer \& Huebscher (2000); (4) Agerer et al.(2001); (5) The
present paper}
\end{table}


\IBVSfig{8cm}{5486-f4.eps}{A possible sudden period decrease of IK Per occurred around E=28000. Symbols are the same as those in Figure 3.}

%%\IBVSfigKey{5486-f4.eps}{IK Per}{O-C diagram}

\references
Agerer, F., Dahm, M., \& Hubscher, J., 2001, {\it IBVS}, No. 5017

Agerer, F., \& Hubscher, J., 2000, {\it IBVS}, No. 4912

Huebscher, J., et al., 1993, {\it B.A.V.Mitt.}, {\bf No. 62}

Huebscher, J., et al., 1994, {\it B.A.V.Mitt.}, {\bf No. 68}

Kholopov, P. N., et al., 1987, {\it The Fourth Edition of General Catalogue
of Variable Stars}, Vol.III, Moscow, Nauka.

Kinnunen, T. \& Skiff, B. A., 2000, {\it IBVS}, No. 4896

Kreiner, J. M., Kim, C.-H., and Nha, I.-S., 2000, {\it An Atlas of O--C Diagrams of Eclipsing Binary Stars}, Cracow, Poland: Wydawnictwo Naukowe Akademii
Pedagogicznej, 2000.

\endreferences

\end{document}
