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\input ibvs2.sty
\begin{document}

\IBVShead{4581}{15 April 1998}

\IBVStitletl{Detection of the $\delta$ Scuti Oscillation in RZ Cassiopeiae}

\IBVSauth{Osamu OHSHIMA$^1$, Shin-ya NARUSAWA$^2$, Hidehiko AKAZAWA$^3$, Mitsugu FUJII$^4$,}
\IBVSauth{Tetsuya KAWABATA$^5$, Nobuo OHKURA$^6$}

\IBVSinst{Kamogata Senior High-School, Kamagata, Okayama, 719-0243 Japan
E-mail: ohshima@po.harenet.or.jp}
\IBVSinst{Nishi-Harima Astronomical Observatory, Sayo, Hyogo, 679-5313
Japan E-mail: narusawa@nhao.go.jp}
\IBVSinst{107 Funao, Okayama, 710-0261 Japan  E-mail: akazawa@sqr.or.jp}
\IBVSinst{Fujii-Bisei Observatory, 4500 Kurosaki, Tamashima, Okayama 
713-8126 Japan  E-mail: aikow@po.harenet.or.jp}
\IBVSinst{Bisei Astronomical Observatory, Bisei, Okayama 714-1411 Japan 
E-mail: kawabata@bao.go.jp}
\IBVSinst{25 Senoh, Okayama 701-0205 Japan  E-mail: HAE00500@niftyserve.or.jp}


\IBVSabs{PMT and CCD photometry of the RZ Cas were carried out. The 22-min} 
\IBVSabs{periodic oscillations with amplitude of about 20-mmag amplitude were}
\IBVSabs{detected not only in primary minimum but also in secondary minimum and}
\IBVSabs{in out-of-eclipse. The oscillations should be the Delta Scuti variability.}

\SIMBADobj{RZ Cas}
\IBVStyp{ EA/SD }
\IBVStyp{ DSCT }
\IBVSkey{photometry}
\IBVSkey{binaries: eclipsing}
\IBVSkey{stars: oscillation}
\begintext

   We have observed the Algol-type binary system RZ Cas (A3V $+$ K0IV) which
has been known for the unusual changes of the shape of light curves at
the bottom part of the primary minimum ({\it e.g.\/} Narusawa {\it et al.\/}
\ 1994). We have carried out photometric observations to study
\lq\lq quasi-periodic oscillations\rq\rq with a period of about 25 min
and an amplitude of $\pm$ 0.04 magnitude reported by Davis and Balonek
(1996) and Davis (1996). Such an oscillation has been found in an
earlier time by Olson (1982).   
   
\paragraph{}

 The observations were carried out at four sites as shown in Table 1 with
PMT photometers and a CCD camera. The observational journals are
 summarized in Table 2. 
 In earlier PMT photometry,  we used HR\,791=HD\,17929=HIP\,12821 as
a comparison star, until we noticed that the variability of this star is
described in  the Hipparcos/Tycho Catalogue (Perryman, 1997). 
The catalogued period and
amplitude are 1\fday 26819  and 0\fmm 01. In the latter observations HD\,15784
was used  as a comparison star. There is no description of the
variability in the HD\,15784 in the Hipparcos/Tycho Catalogue. 
Even though in the earlier observations, there should be no serious
problem to use HR\,791 as a comparison star, because we studied the
variability on the time scale of 0.01 - 0.02 d which is very short
compared with that of the variability for HR\,719. In the CCD photometry,
we use SAO12413=Tyc4316-00097-1 and HD\,16615=HIP\,12734 as the comparison
and the check star respectively. There are no descriptions of variability
on these stars in  Hipparcos/Tycho catalogue.
 
\paragraph{}
 
   In our all observational data obtained on the photometric nights, we 
have detected the periodic oscillations with the amplitude of twenty
mmag. In Fig. 1, the oscillation in RZ Cas at a primary minimum in $B$-band,
a secondary minimum in $R$-band and an out-of-eclipse in $B$-band are
shown. All light curves indicated here are corrected for the mean light
curves. The correction is performed in the intensity scale. In the
primary minimum, in order to separate the short-term variability from
the light variation caused by the eclipse, we subtract the mean light
curve from observed light curve. The mean light curve we used is the 4th
order polynomial fitted by the least-squares method to the date produced
by folding the observations at the minimum.
  
  
\vspace {4mm}
\begin{table}
\caption{Observational Sites}
\begin{center}
\begin{tabular}{lllll}
\hline
Site &  Observer & Telescope$^1$ & Detector$^2$ &  Integ. Time \\
\hline\\
Funao & Akazawa & 0.28-m S.C.  &  PMT  R647p P.C. &  10 sec. \\
Senoh & Ohkura & 0.35-m S.C. & PMT R647p P.C. & 10 sec.     \\
BAO   & Kawabata & 1.01-m Cass. & PMT R647p P.C. &  10 sec.  \\
FBO   & Fujii & 0.075-m refractor & CCD ST-7      &  10/20 sec. \\
\hline
\end {tabular}
\\

$^1$ S. C. : Schmidt-Cassegrain telescope\\  
$^2$ P. C. : photon-counting system\\
\end{center}
    \label{site}
%\end{table}

%\begin{table}
\caption{Observational Log}
\begin{center}
%\small
\begin{tabular}{lllll}
\hline
Start time & Binary Phase  &  Band & Comparison & Site\\	
(Hel. J. D.) & Coverage &  & Star & \\
\hline              \\
2450747.100 & 0.981 - 0.026  & $B$,$V$ & HR791   & Funao\\
2450753.054 & 0.963 - 0.016  & $B$,$V$ & HR791   & Senoh\\
2450753.093 & 0.995 - 0.010  & $B$,$V$ & HR791   & Funao\\
2450753.264 & 0.139 - 0.196  & $B$,$V$ & HR791   & Funao\\
2450759.055 & 0.984 - 0.015  & $B$,$V$ & HR791   & Senoh\\
2450759.077 & 0.002 - 0.021  & $B$,$V$ & HR791   & Funao\\
2450770.997 & 0.975 - 0.029  & $B$,$V$ & HR791   & Senoh\\
2450771.008 & 0.985 - 0.015  & $R$     & HD12413 & FBO  \\
2450771.024 & 0.998 - 0.026  & $B$,$V$ & HR791   & Funao\\
2450776.987 & 0.986 - 0.024  & $B$,$V$ & HR791   & Funao\\
2450776.992 & 0.991 - 0.022  & $B$,$V$ & HR791   & Senoh\\
2450786.163 & 0.663 - 0.721  & $B$,$V$ & HR791   & Senoh\\
2450787.078 & 0.429 - 0.502  & $R$     & HD12413 & FBO  \\
2450788.042 & 0.235 - 0.244  & $B$,$V$ & HD15784 & Funao\\
2450788.078 & 0.266 - 0.321  & $B$,$V$ & HD15784 & Senoh\\
2450793.038 & 0.415 - 0.510  & $B$,$V$ & HD15784 & Funao\\
2450793.047 & 0.423 - 0.518  & $B$,$V$ & HD15784 & Senoh\\
2450800.945 & 0.031 - 0.281  & $R$     & HD12413 & FBO  \\
2450801.048 & 0.117 - 0.230  & $B$,$V$ & HD15784 & Funao\\
2450801.055 & 0.123 - 0.181  & $V$     & HD15784 & BAO  \\
2450805.998 & 0.259 - 0.319  & $B$,$V$ & HD15784 & Funao\\
2450806.025 & 0.281 - 0.366  & $B$,$V$ & HD15784 & Senoh\\
2450807.024 & 0.117 - 0.217  & $B$,$V$ & HD15784 & Senoh\\
2450808.000 & 0.934 - 0.011  & $B$,$V$ & HD15784 & Funao\\
2450808.005 & 0.937 - 0.060  & $U$,$B$,$V$ & HD15784 & Senoh \\
2450825.975 & 0.972 - 0.033  & $B$,$V$ & HD15784 & Senoh\\
2450829.970 & 0.392 - 0.374  & $B$,$V$ & HD15784 & Funao\\
2450830.063 & 0.314 - 0.515  & $B$,$V$ & HD15784 & Senoh\\
\hline
\end {tabular}
\end{center}
    \label{observation}
\end{table}


 \IBVSfig{100mm}{4581-f1.ps}{ Observed oscillations at various binary phases
of RZ Cas. Upper, middle and lower light curves obtained at a primary
minimum in B-band, a secondary minimum in R-band and an out-of-eclipse in
B-band respectively}

\IBVSfig{97mm}{4581-f2.ps}{
 a) The relative variance, Theta, for all B-band observations derived from 
the PDM analysis. The periodicity is found at 0.0155766 and 0\fday 0157812
with multi-periodic feature. b) The five-point running mean values
plotted with one of the most dominant period, 0\fday 00155766}
   
 
 
 We adapted the PDM analysis (Widjaya, 1996) to B-band photometric data 
with a time span of 83 days. 
In Fig. 2, the relative variance of data set,
theta, is illustrated in the upper subfigure. The periodicity is found 
at the period of 0.0155766 (frequency = 64\fday 199$^{-1}$) 
and 0\fday 0157812   (63\fday 367$^{-1}$) with multi-periodic feature.  
The detailed analysis of light curve should be performed more 
carefully. 
In the lower subfigure, the five-point running averaged magnitudes are
plotted with the phase. Since the spectral type of the primary is A3V, 
we can see the star is in the bluest group of known $\delta$ Scuti stars 
and also included in the theoretical instability strip for the $\delta$ 
Scuti stars ({\it e.g.\/} see Moskalik 1995).
The period of 0\fday 016  is not typical one of the $\delta$ Scuti stars, 
but is not too short because the periods of the shortest known 
$\delta$ Scuti stars are 0\fday 0205  and 0\fday 03  for V624 Tau and 
V377 Cas, besides 0\fday 0084  for a suspected member of the group 
V816 Cen. We conclude that the oscillations in RZ Cas we detected are 
the $\delta$ Scuti variability and that RZ Cas may be the shortest 
period star in the known $\delta$ Scuti stars. 
The relation between amplitude and color variations in the oscillation
of RZ Cas shown in Fig. 11 of Olson (1982) justly indicates the character
of the $\delta$ Scuti oscillation. 
 
 We suppose that the temporal changes of the shape of light curves during 
the primary minima were caused from the superposition of the delta Scuti
type oscillation of the A3 component. Detailed analysis of the light
curve  will be published elsewhere.
 
\paragraph{}

 We express our gratitude to Prof. Mine Takeuti and Dr. Tosihito Ishida
for their useful discussion on the Delta Scuti oscillations, and to Dr.
Taichi Kato for his critical advice. We also appreciate the encouragement
of Prof. Atsuma Yamasaki and Prof. Yasuhisa Nakamura to our observations.
One of the authors (S. N.) thanks to Dr. W. Osborn of Central Michigan
University for his kindly sending the paper of Davis (1996). 
 
\references
Davis, S.M. and Balonek, T.J., 1996, {\it B.A.A.S.}, 1375

Davis, S.M., 1996, {\it in Proceedings of the 1996 Keck Undergraduate 
Symposium on Research in Astronomy}, 29

Moskalik, P., 1995, {\it ASP Conf. Ser}. {\bf 83}, 44, 
      {\it in Astrophysical application of stellar pulsation},
      Proc. IAU Coll. 155, {\it eds.} R. S. Stobie, P. A. Whitelock,
%Changed: Thu Jun  2 16:13:51 MEST 2005
      
Narusawa, S., Nakamura, Y. and Yamasaki, A., 1994, {\it A.J.}, {\bf 107},
1141

Olson, E.C., 1982, {\it Ap.J.}, {\bf 259}, 702

Perryman, M.A.C., 1997, {\it The Hipparcos and Tycho Catalogues Search 
facility}, \\
http://astro.estec.esa.nl/SA-general/Projects/Hipparcos/
HIPcatalogueSearch.html

Widjaya, A., 1996, {\it Phase Dispersion Minimization for Windows Ver. 3.0},\\
http://www.kusastro.kyoto-u.ac.jp/vsnet/etc/prog.html


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