\documentstyle[twoside,ibvs2,ibvst,ibvse,epsf]{article}

\begin{document}

\IBVShead{5314}{9 September 2002}

\IBVStitletl{Detection of a Pulsating Component}{ in the Eclipsing Binary RX H\lowercase{ya}}

\IBVSauth{Kim, S.-L.$^1$; Kwon, S.-G.$^1$; Youn, J.-H.$^1$; Mkrtichian, D.E.$^2$; Lee, J.W.$^3$}

\IBVSinst{Korea Astronomy Observatory, Daejeon, 305-348, Korea (e-mail : slkim@kao.re.kr)}
\IBVSinst{Astronomical Observatory, Odessa National University, Odessa, Ukraine}
\IBVSinst{Dept. of Astronomy and Space Science, Chungbuk National University, Cheongju, 361-763, Korea}

\SIMBADobj{RX Hya}
\IBVStyp{ EA/SD }
\IBVSkey{pulsation, eclipse, photometry}

\IBVSabs{We report detection of a pulsating component in the Algol type}
\IBVSabs{eclipsing binary RX Hya}


\begintext

\IBVSTobs{Sobaeksan Optical Astronomy Observatory, 61cm telescope}

\IBVSTdet{SITe 2K CCD camera}

\IBVSTfil{$B$}

\IBVSTsysn

\IBVSTdata{Upon request}

\IBVSEred{Standard CCD-frame reduction using the IRAF\footnotemark[1] package.}
\footnotetext[1]{IRAF is distributed by the National Optical Astronomy Observatories, which are operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation.}


\begin{table}[h]
\centerline{{\bf Table 1.} Photometric parameters of observed stars}
\begin{center}
\begin{tabular}{clccccc}
\hline
\hline
\noalign{\smallskip}
ID  & Name & RA (J2000) & DEC (J2000) & V & (B$-$V) & Sp. Type \\
\noalign{\smallskip}
\hline
\noalign{\smallskip}
VAR & RX Hya       & 09\hr 05\mm 41\fsec16 & $-$08\deg 15\arcm 39\farcs7 & 8\fmm9$\sim$11\fmm6$^\dagger$ & 0\fmm20 & A8$^\dagger$ \\
C1  & BD$-$07\deg 2718 & 09\hr 06\mm 16\fsec58 & $-$08\deg 06\arcm 44\farcs5 & 9\fmm70 & 1\fmm40 & $-$  \\
C2  &              & 09\hr 05\mm 40\fsec89 & $-$08\deg 15\arcm 23\farcs0 & 11\fmm5$^\ddagger$ &     $-$   & F3$^\ddagger$ \\
\noalign{\smallskip}
\hline
\end{tabular}
\end{center}

$^\dagger$ : from the GCVS (Kholopov et al. 1988)\\
$^\ddagger$ : Vyas \& Abhyankar (1989) 
\end{table}

\IBVSfig{10.5cm}{5314-f1.eps}{
An observed CCD image (20$\farcm$5$\times$20$\farcm$5) near the eclipsing binary RX Hya (VAR). The comparison star 
(C1, BD$-$07\deg2718) and the check star (C2) are marked. North is up and east is to the left}
%\IBVSfigKey{5314-f1.eps}{RX Hya}{finding chart}

\IBVSfig{5.4cm}{5314-f2.eps}{
Differential magnitudes of the variable and check stars, after correction for the second-order 
atmospheric extinction. Sinusoidal curves with semi-amplitude of 7.0 mmag and frequency of 19.39 cycles/day,
obtained in this study, are superimposed in the upper panels}
%\IBVSfigKey{5314-f2.eps}{RX Hya}{light curve}

\IBVSfig{8.4cm}{5314-f3.eps}{
Power spectra of the variable and check stars. Window spectrum is in the top panel.
The dominant pulsation frequency of the variable star RX Hya is shown at 19.39 cycles/day in the middle panel. 
The spectrum of the check star plotted in the bottom panel shows only noise-level powers} 
%\IBVSfigKey{5314-f3.eps}{RX Hya}{periodogram}

\IBVSTrem{
As a part of the observational survey to search for A-F spectral type pulsating components in eclipsing binary systems, in collaboration with the Central Asian Network group (Mkrtichian et al. 2002a), we performed time-series 
CCD observations of the eclipsing binary RX Hya in February 28 and March 1, 2002, with $B$ filter.
Among several stars near the variable star, the brightest star BD$-$07\deg2718 was chosen as comparison star.
We applied simple aperture photometry to get instrumental magnitudes with an aperture radius of 6\farcs0; 
typical atmospheric seeing was about 2\farcs7 during the observing runs. \\
We observed the variable star during out-of eclipsing orbital phases around 0.77 (H.J.D. 2452334.2) 
and 0.18 (H.J.D. 2452335.1), calculated from the GCVS data (Kholopov et al. 1988). 
Differential magnitudes were calculated according the standard differential photometric method.
We corrected for the second-order atmospheric extinction effect, the slow airmass-related light variation,
because the color index of the comparison star was quite different from that of the variable star 
and the data were obtained at large airmasses ranging from 1.4 to 2.5. \\
We have clearly detected oscillation features of the variable star RX Hya  (Figure 2).
In order to derive its period, we performed Fourier analysis (Kim \& Lee 1996). 
Figure 3 displays power spectra of the variable and check stars.
We obtained a dominant frequency of 19.39 cycles/day and a semi-amplitude about 7 mmag in B-band for the variable star. 
}

\vfill

\IBVSTrem{
Mkrtichian et al. (2002b) suggested a new pulsating group defined as ``the (B)A-F spectral type mass-accreting main-sequence 
pulsating stars in semi-detached Algol-type binary systems''. Their pulsation characteristics are very similar to those of
$\delta$ Scuti type stars, but this evolution is different due to mass-accretion.
Considering spectral type, sinusoidal light curves, frequency and amplitude of pulsation, 
and the membership in a semi-detached Algol type system,
we suggest that the primary component of RX Hya is a new, seventh member of this pulsating group.
}

\IBVSTack{This research made use of the SIMBAD database, operated at CDS, Strasbourg, France}

\reference

Kholopov, P.N., Samus, N.N., Frolov, M.S., et al., 1988, in {\it General Catalogue of Variable Stars}, 
4th Edition (Moscow: Nauka Publishing House)

Kim, S.-L., Lee, S.-W., 1996, {\it A\&A}, {\bf 310}, 831

Mkrtichian, D.E., Kusakin, A.V., Gamarova, A.Yu., et al., 2002a, {\it ASP Conf.
 Ser.}, {\bf 256}, 259, in {\it Observational aspects of pulsating B \& A 
stars}, ed. C. Sterken, \& D.W. Kurtz
%Changed : Tue May 31 17:09:03 MEST 2005

Mkrtichian, D.E., Kusakin, A.V., Gamarova, A.Yu., Nazarenko, V., 2002b, 
{\it ASP Conf. Ser.}, {\bf 259}, 96, in {\it Radial and nonradial pulsations
as probes of stellar physics}, ed. C. Aerts, T.R. Bedding, \& J. Christensen-Dalsgaard
%Changed : Tue May 31 17:09:03 MEST 2005

Vyas, M.L., Abhyankar, K.D., 1989, {\it A\&AS}, {\bf 81}, 67

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