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\IBVShead{5572}{26 October 2004}

\IBVStitletl{Discovery of a short-periodic pulsating component}{ in the Algol-type eclipsing binary system TU H\lowercase{er}}

\IBVSauth{Lampens, P.$^1$; Van Cauteren, P.$^2$; Strigachev, A.$^3$; Kim, S.-L.$^4$; Kang, Y. B.$^4$; Koo, J.-R.$^4$; Mkrtichian, D. E.$^{5,6}$}

\IBVSinst{Koninklijke Sterrenwacht van Belgi\"e, B--1180 Brussel, Belgium (email : patricia.lampens@oma.be)}
\IBVSinst{Beersel Hills Observatory, Laarheidestraat 166, B-1650 Beersel, Belgium }
\IBVSinst{Institute of Astronomy, Bulgarian Academy of Sciences, 72 Tsarigradsko Chausse Blvd., 1784 Sofia, Bulgaria }
\IBVSinst{Korea Astronomy Observatory, Daejeon, 305-348, Korea }
\IBVSinst{ARCSEC, Sejong University, Seoul, 143-747, Korea }
\IBVSinst{Astronomical Observatory, Odessa National University, Shevchenko Park, Odessa, 65014, Ukraine }

\SIMBADobjAlias{TU Her}{GSC 02591-00132}
\IBVStyp{ EA/SD }
\IBVSkey{Photometry - eclipsing binary - pulsation}
\IBVSabs{We report the discovery of rapid pulsations of the type delta Scuti}
\IBVSabs{in the semi-detached eclipsing binary system TU Her.}


\begintext

\vspace*{-1cm}

As a part of international photometric survey projects to search for A-type pulsating components in eclipsing binary 
systems (Mkrtichian et al. 2002; Kim et al. 2003), we monitored several candidate targets during spring 2004 using 
telescopes across Europe and in the US. The instruments used were the 1.0 m telescope of the Universit\"atssternwarte 
Hoher List (OHL, Bonn, Germany), the 1.3 m Ritchey-Chr\'etien telescope of the Skinakas Observatory\IBVSfm \,(SKI, Crete)
the 1.0 m telescope of the Mt. Lemmon Optical Astronomy Observatory (LOAO, USA) and the 0.4 m telescope of the Beersel 
Hills Observatory (BHO, Belgium). These telescopes were respectively equipped with the 2K$\times$2K HoLiCam CCD (OHL), a 
1K$\times$1K CH360 CCD (SKI), a 2K$\times$2K CCD (LOAO) and a \hbox{1.5K$\times$1K ST-10 CCD (BHO)}. 

\IBVSfoot{The Skinakas Observatory is a collaborative project of the University of Crete, the Foundation for Research 
and Technology -- Hellas, and the Max-Planck-Institut f\"ur Extraterrestrische Physik.}

The eclipsing binary system TU Her was monitored during 1 (partial) night at the Hoher List Observatory (filter Johnson $V$), three 
(partial) nights at Beersel Hills Observatory (filters Johnson $V$ and $B$), 1 (full) night at the Skinakas Observatory (filter 
Johnson $B$) and two (partial) nights at Mt. Lemmon Observatory (filter Johnson $B$). 
In total we observed two eclipses and obtained out-of-eclipse data during the remaining four nights. The same comparison star 
C1 was used at all the sites. Additional comparison stars were observed when the CCD's fields were sufficiently large 
(larger than 8\farcm5$\times$8\farcm5). From the first runs at BHO we suspected small-amplitude short-periodic 
oscillations in the light of TU Her (cf. Fig.~2, upper left panel). Follow-up observations to confirm these rapid variations were next 
performed at Skinakas and Mt. Lemmon in June and July 2004. These data are available upon request.

\IBVSfig{9.5cm}{5572-f1.eps}{Field of the eclipsing binary TU Her (field size is 24$\arcm$$\times$16$\arcm$). 
The comparison (C1) and check stars (C2,C3,C4) are also marked. North is up and east is to the left.}
\IBVSfigKey{5572-f1.eps}{TU Her}{finding chart}

\begin{table}[!h]
\centerline{{\bf Table 1.} Photometric properties of target and comparison stars from the Tycho-2}
\centerline{\hspace*{2.0cm}catalogue (ESA 1997)}
\begin{center}
\begin{tabular}{clccccc}
\hline
\hline
\noalign{\smallskip}
ID  & Name/GSC & RA (J2000) & DEC (J2000) & $V_T$ & $(B_T-V_T)$ & Observatory\\
\noalign{\smallskip}
\hline
VAR & TU Her  & 17\hr 13\mm 35\fsec37 & +30\deg 42\arcm 36\farcs0 & 11\fmm153 & 0\fmm123 & all\\
C1  & 02591-00191 & 17\hr 13\mm 58\fsec96 & +30\deg 45\arcm 16\farcs3 & 10\fmm597 &-0\fmm197 & all\\
C2  & 02591-00264 & 17\hr 14\mm 03\fsec35 & +30\deg 36\arcm 45\farcs9 & 11\fmm225 & 0\fmm852 & BHO; LOAO \\
C3  & 02591-00115 & 17\hr 13\mm 01\fsec78 & +30\deg 43\arcm 16\farcs0 & 11\fmm473 & 0\fmm522 & LOAO \\
C4  & 02591-00161 & 17\hr 13\mm 48\fsec44 & +30\deg 44\arcm 35\farcs5 & (12\fmm9) & -- & OHL\\
\hline
\end{tabular}
\end{center}
\vspace*{0.45cm}
\end{table}

\vspace*{-0.4cm}

Standard aperture photometry was applied to all the frames to obtain differential instrumental magnitudes with respect to 
C1 as well as a few other comparison stars. Fig.~1 displays a sample CCD image of the field. Also indicated are the positions 
of the comparison and check stars. Several light curves acquired in the $V$ and $B$ passbands are shown in Figs.~2 and 3. 
From the out-of-eclipse light curves one can clearly distinguish short-periodic oscillations with a peak-to-peak amplitude 
of about 0.02 mag. A preliminary analysis of the data out-of-eclipse shows a main periodicity near 18 ($\pm$ 0.2) c/d with a 
semi-amplitude of only 4-5 mmag. 

\IBVSfig{9.0cm}{5572-f2.eps}{Light curves obtained at Beersel Hills, Skinakas and Hoher List observatories: 
differential magnitudes between the variable star TU Her and the main comparison star, $\Delta V$(V$-$C1) resp. 
$\Delta B$(V$-$C1). In one instance, the differential data of the check star $\Delta V$(C2$-$C1) are displayed 
for comparison (lower left). On 01/02-04-2004, a total primary eclipse was observed (lower right).}
\IBVSfigKey{5572-f2.eps}{TU Her}{light curve}

\IBVSfig{8.0cm}{5572-f3.eps}{Two light curves obtained at Mt. Lemmon Observatory: differential magnitudes 
between the variable star TU Her and the main comparison star, $\Delta B$(V$-$C1). Differential data of the 
check star, $\Delta B$(C2$-$C1), are displayed in the lower panels for comparison.}
\IBVSfigKey{5572-f3.eps}{TU Her}{lightcurve}

\begin{table}[h]
\centerline{{\bf Table 2.} Times and residuals for two new mid-eclipse events of TU Her}
\begin{center}
\begin{tabular}{ccccc}
\hline
\hline
\noalign{\smallskip}
   HJD $\pm$ error  &  Min. & Cycle Nr. & Predicted HJD  & ($O-C$) \\
\noalign{\smallskip}
\hline
  2453097.5800 $\pm$ 0.0008 & I & 6897 &  2453097.4651  &  0.1149\\
  2453215.4615 $\pm$ 0.0005 & I & 6949 &  2453215.3429  &  0.1186\\
\hline
\end{tabular}
\end{center}
\end{table}

Total eclipses were observed on two occasions: on the night of April 01/02, 2004 at OHL and on the night of 
July 28/29, 2004 at BHO (see also Fig. 4). These phenomena were used to compute two new times of mid-eclipse. TU Her, with a period of 
2.2671~days in the GCVS catalogue (Kholopov et al. 1988), shows a rapidly decreasing orbital period (Shengbang 2000). 
Table~2 lists the new times and their residuals with respect to the quadratic ephemeris determined by Shengbang 
(2000) (cf. equ. 6). The increasing residuals indicate that the observed times (again) deviate from their expected 
values.

\IBVSfig{4cm}{5572-f4.eps}{Light curve obtained at BHO showing a total eclipse of TU Her.}
\IBVSfigKey{5572-f4.eps}{TU Her}{light curve}

\vspace*{-0.45cm}

The new pulsating variable star is classified as of spectral type A5 (SIMBAD, CDS), but also F0 III/IV (Halbedel 
1984). In view of the similarity between the characteristics of the shown light curves and those typical
of a $\delta$ Scuti star (period, amplitude), the spectral type and the semi-detached binary
configuration, we propose that TU Her is a new member of the group of mass-accreting pulsating components 
in Algol-type eclipsing binary systems (oEA stars; cf. Table~3 in Mkrtichian et al. 2004). Thus the number of known oEA stars 
is presently thirteen, including the recent discoveries of four new oEA stars during this same year (Caton 2004; 
Kim et al. 2004a, 2004b).\\ 

{\bf Acknowledgements}
We thank Prof.~I.~Papamastorakis, director of Skinakas Observatory, Dr.~I.~Papadakis and Dr.~K.~Reif, director
of the Sternwarte Hoher List for the allocated telescope time and the hospitality. PL and AS acknowledge support from 
the Belgian Science Policy and from the Bulgarian Academy of Sciences (project BL/33/B11). PL and PVC are 
grateful to the Fund for Scientific Research (FWO) - Flanders (Belgium) (project G.0178.02). Part of these data were 
acquired with equipment purchased thanks to a research fund financed by the Belgian National Lottery (1999). We made 
use of the SIMBAD database from the {\it Centre de Donn\'ees Astronomiques}, Strasbourg, France.


\references 

Caton, D.B., 2004, {\it IBVS}, No. 5531

ESA, 1997,  `The Hipparcos and Tycho Catalogues', ESA SP-1200

Halbedel, E., 1984, {\it IBVS}, 2549

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, J.W., Kwon, S.-G., et al., 2003, {\it A\&A}, {\bf 405}, 231

Kim, S.-L., Koo, J.-R., Lee, J.A., et al., 2004a, {\it IBVS}, 5537

Kim, S.-L., Kang, Y. B., Koo, J.-R., et al., 2004b, {\it IBVS}, 5538

Mkrtichian, D.E., Kusakin, A. V., Gamarova, A. Yu. et al., 2002, ASP Conf. Ser. {\bf 256}, 259 
               (eds. C. Aerts, T. R. Bedding \& J. Christensen-Dalsgaard)
%Original: {\bf 256}, eds. C. Aerts, T. R. Bedding \& J. Christensen-Dalsgaard, 259
%Corrected: Tue Feb  8 08:54:08 MET 2005

Mkrtichian, D.E., Kusakin, A.V., Rodr\'{\i}guez, E., et al., 2004, {\it A\&A}, {\bf 419}, 1015

Shengbang, Q., 2000, {\it AJ}, {\bf 119}, 901

\endreferences 

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