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\IBVShead{5856}{22 October 2008}

\IBVStitletl{Short-period oscillations in the Algol-type systems II:}{ Newly discovered variable GSC 3889-0202}

\IBVSauth{Dimitrov, D.; Kraicheva, Z.; Popov, V.}

\IBVSinsto{Institute of Astronomy, BAS, Tsarigradsko Shossee 72, 1784 Sofia, Bulgaria, \\ e-mail: dinko@astro.bas.bg; zk@astro.bas.bg; vpopov@astro.bas.bg}

\SIMBADobjAlias{GSC 3889-0202}{TYC 3889-0202-1}
\IBVStyp{ oEA }
\IBVSkey{eclipsing binaries, oscillating variables, photometry, spectroscopy}
\IBVSabs{On the basis of the NSVS data search a new Algol-type system GSC 3889-0202}
\IBVSabs{with orbital period of about 2.71 days and amplitude of}
\IBVSabs{primary minimum > 0.35 mag was discovered.}
\IBVSabs{Short-period oscillations with amplitude up to 0.045 mag in R and}
\IBVSabs{main periodicity of about 63.47 minutes were found during}
\IBVSabs{our CCD observations of the variable.}

\begintext

GSC 3889-0202 was discovered as a new eclipsing binary in our search for new variables in the NSVS database (Wozniak et al. 2004). According to the NSVS data the star was classified as Algol-type binary with period $P \simeq 2.71$ days, amplitude of primary minimum $A_R > 0.35$ mag, and the magnitude in maximum $R'\mbox{max} \simeq 10.6$ mag.

The CCD photometry (in $BVR$ bands) of GSC 3889-0202 was carried out with the 60cm Cassegrain telescope at NAO Rozhen, equipped with the CCD camera FLI PL09000 (3056x3056, 12$\mu$ pixel), and Bessell (1990) standard $UBVRI$ filters. The standard IRAF procedures were used for the reduction of the photometric data. There are no suitable standards in the field (Fig. 1) and we apply the photometry method of Everett and Howell (2001). An ensemble standard star (COMP) was created using four stars (Table 1) with $\sigma < 0.013$ mag in all $R$ band observations.

The phased light curves, based on the NSVS data and Rozhen observations, are shown on Fig. 2. The light curves for several nights, acquired in the $BVR$ passbands are shown in Fig. 4 and Fig. 5. Short-period oscillations with a peak-to-peak amplitude of up to 0.045 mag in $R$ (Table 2), 0.05 mag in $V$, and 0.07 mag in $B$ (also present at the primary and the secondary minima) were detected. A preliminary periodogram analysis (Fig. 6) of the data shows a main periodicity of about 22.69 c/d ($\sim$ 63.47 minutes).

Spectral observations of GSC 3889-0202 were obtained with the Coud\'e spectrograph (resolution of 0.19 \AA{}/pixel) of the 2m RC telescope at NAO Rozhen (Table 3). The spectral domain covered three regions around H$_\alpha$, H$_\beta$, and MgII 4481 lines (Fig. 3). The data reduction of the spectra was made with the standard IRAF procedures. The corresponding radial velocities were measured by the cross-correlation technique using synthetic spectrum,  calculated with the programme SPECTRUM (Gray \& Corbally 1994) and a grid of LTE atmosphere models for a solar-type chemical composition (Castelli \& Kurucz 2003), as a template spectrum. The physical parameters of the primary component were estimated by comparing the synthetic and the observed spectra. The parameters of the secondary were computed with the PHOEBE software (Pr\v{s}a \& Zwitter 2005). The spectral types of the two components were determined using Gray \& Corbally (1994) calibration (Table 4). The amplitude of the RV curve was estimated to be $A_{RV} \geq 60$ kms$^{-1}$, and the $\gamma$ velocity is -16.2 kms$^{-1}$ (Fig.~2).

The new ephemeris were computed using both Rozhen and NSVS data:

\begin{equation}
HJD(\mbox{MinI})  =  2454620.151(\pm0.004) + 2.71066(\pm 0.00008) E
\end{equation} 

\textbf{Acknowledgements} This study made use of the SIMBAD, ADS, and VSX databases, and GCVS catalogue.


\centerline{Table 1. Data for the variable, comparison, and check stars used in the CCD photometry}
\vskip 3mm
\begin{center}
\begin{tabular}{ccccc}
\hline
ID   & Name  & RA (J2000) & DEC (J2000)   & $B_T-V_T$  \\
\hline
VAR & GSC 3889-0202 & 17$^h$ 46$^m$ 30.43$^s$ & +53$^\circ$ 11$^\prime$ 57.8$^{\prime\prime}$ & 0.244 \\
C1  & GSC 3902-0709 & 17$^h$ 46$^m$ 50.63$^s$ & +53$^\circ$ 12$^\prime$ 32.8$^{\prime\prime}$ & 1.158 \\
C2  & GSC 3889-0120 & 17$^h$ 46$^m$ 24.77$^s$ & +53$^\circ$ 12$^\prime$ 07.7$^{\prime\prime}$  &  \\
C3  & GSC 3889-0906 & 17$^h$ 46$^m$ 38.61$^s$ & +53$^\circ$ 12$^\prime$ 27.6$^{\prime\prime}$  &  \\
C4  & GSC 3889-0216 & 17$^h$ 46$^m$ 28.79$^s$ & +53$^\circ$ 09$^\prime$ 16.5$^{\prime\prime}$  &  \\
\hline
\end{tabular}
\end{center}


\centerline{Table 2. Observational runs of GSC 3889-0202}
\vskip 3mm
\begin{small}
\begin{center}
\begin{tabular}{cccccccc}
\hline
Date   &  HJD(start)  &  Length & Filter   & Exp. [s] &  N  & Phase & $A_R$max(osc.) \\
\hline
05.06.2008  &  2454623.50080  &  01$^h$ 44$^m$  &  $R$  &  60  &  83  &  0.24-0.27  &  0.02  \\ 
27.06.2008  &  2454645.48054  &  02$^h$ 18$^m$  &  $BVR$ &  120,60,30  &  35  &  0.35-0.38  &   -   \\ 
29.06.2008  &  2454647.45583  &  01$^h$ 45$^m$  &  $R$  &  60  &  99  &  0.08-0.10  &  0.045  \\ 
30.06.2008  &  2454648.47006  &  02$^h$ 38$^m$  &  $R$  &  60  &  135  &  0.45-0.49  &  0.03  \\ 
01.07.2008  &  2454649.45747  &  01$^h$ 45$^m$  &  $R$  &  60  &  98  &  0.81-0.84  &  0.02  \\ 
03.07.2008  &  2454651.46105  &  02$^h$ 10$^m$  &  $R$  &  60  &  119  &  0.55-0.59  &  0.03  \\ 
06.07.2008  &  2454654.40236  &  02$^h$ 21$^m$  &  $R$  &  30  &  239  &  0.64-0.67  &  0.015  \\ 
17.07.2008  &  2454665.48791  &  01$^h$ 33$^m$  &  $R$  &  60  &  79  &  0.73-0.75  &  0.015  \\ 
18.07.2008  &  2454666.44853  &  01$^h$ 46$^m$  &  $R$  &  60  &  99  &  0.08-0.11  &  0.035  \\ 
25.07.2008  &  2454673.32356  &  00$^h$ 20$^m$  &  $R$  &  60  &  19  &  0.61-0.62  &   -   \\ 
02.08.2008  &  2454681.40295  &  03$^h$ 18$^m$  &  $BVR$  &  120,60,30  &  49  &  0.60-0.65  &  0.02  \\ 
03.08.2008  &  2454682.52403  &  00$^h$ 54$^m$  &  $BVR$  &  120,60,30  &  14  &  0.01-0.03  &   -   \\ 
04.08.2008  &  2454683.51846  &  01$^h$ 19$^m$  &  $BVR$  &  120,60,30  &  19  &  0.38-0.40  &  0.03  \\ 
05.08.2008  &  2454684.51287  &  01$^h$ 15$^m$  &  $BVR$  &  120,60,30  &  19  &  0.75-0.77  &  0.04  \\ 
06.08.2008  &  2454685.26067  &  05$^h$ 31$^m$  &  $R$  &  60  &  252  &  0.02-0.11  &  0.02  \\ 
07.08.2008  &  2454686.31423  &  05$^h$ 42$^m$  &  $BVR$  &  120,60,30  &  89  &  0.41-0.50  &  0.025  \\ 
11.08.2008  &  2454690.29035  &  07$^h$ 42$^m$  &  $BVR$  &  120,50,20  &  127  &  0.88-1.00  &  0.035  \\ 
06.09.2008  &  2454716.28481  &  04$^h$ 31$^m$  &  $BVR$  &  120,60,30  &  57  &  0.47-0.54  &  0.04  \\ 
\hline
\end{tabular}
\end{center}
\end{small}


\centerline{Table 3. Rozhen spectra of GSC 3889-0202}
\vskip 3mm
\begin{center}
\begin{tabular}{cccccrcc}
\hline
  Date     &  HJD(mid)   & S/N & Exp. & \multicolumn{2}{c}{RV}  &  Region & Phase \\
               &         &       &   [s]  &  \multicolumn{2}{c}{[kms$^{-1}$]} &  [\AA{}]&  \\
\hline
10.06.2008 & 2454628.5088 & 39 & 1800 &  -40.8 & $\pm$1.7 &  4400-4600 & 0.094\\
10.06.2008 & 2454628.4841 & 51 & 1800 &  -35.4 & $\pm$6.5 & 4800-5000 & 0.084\\
10.06.2008 & 2454628.4612 & 63 & 1800 &  -36.0 & $\pm$4.3 & 6500-6700 & 0.076\\
11.06.2008 & 2454629.4740 & 38 & 1800 &  -32.7 & $\pm$1.6 &  4400-4600 & 0.450\\
11.06.2008 & 2454629.4968 & 52 & 1800 &  -25.9 & $\pm$6.8 & 4800-5000 & 0.458\\
11.06 2008 & 2454629.5197 & 63 & 1800 &  -24.3 & $\pm$2.3 & 6500-6700 & 0.467\\
12.06.2008 & 2454630.5328 & 35 & 1800 &  +17.2 & $\pm$1.8 &  4400-4600 & 0.840\\
12.06.2008 & 2454630.5096 & 48 & 1800 &  +22.4 & $\pm$5.7 & 4800-5000 & 0.832\\
12.06 2008 & 2454630.4864 & 58 & 1800 &  +24.6 & $\pm$2.6 & 6500-6700 & 0.823\\
\hline
\end{tabular}
\end{center}

\centerline{Table 4. Physical parameters of the primary and secondary components of GSC 3889-0202}
\vskip 3mm
\begin{center}
\begin{tabular}{cccc}
\hline
 \multicolumn{2}{c}{Parameter}     & Primary star   & Secondary star \\
\hline
$T_{\mbox{eff}}$ & [K] & 7750 & 4500 \\
$\log g$ & & 3.9 & 3.2\\
$v \sin i$ & [kms$^{-1}$] &  $\sim 60$ & \\ 
Spectral type & & A7 V-IV & K III \\
\hline
\end{tabular}
\end{center}



\IBVSfig{8cm}{5856-f1.eps}{Field of the eclipsing binary GSC 3889-0202 (size $15' \times 10'$). North is down and East is to the right.}
\IBVSfigKey{5856-f1.eps}{GSC 3889-0202}{finding chart}
\IBVS2fig{7.8cm}{5856-f2.eps}{Light and radial velocity curves of GSC 3889-0202. Upper panel - NSVS data, midlie panel - Rozhen R data (dots) and model (solid line), and lower panel - Rozhen RV data (diamonds) and model (solid line).}{5856-f3.eps}{Rozhen combined spectra (thin line) of GSC 3889-0202  and the best synthetic spectra (thick~line).}
\IBVSfigKey{5856-f2.eps}{GSC 3889-0202}{light curve ; radial velocity curve}
\IBVSfigKey{5856-f3.eps}{GSC 3889-0202}{spectrum}
\newpage
\IBVS2fig{7.5cm}{5856-f4.eps}{Sample $\Delta R$ light curves of GSC 3889-0202 (VAR--COMP, diamonds) and properly shifted C3 star (C3--COMP, crosses). Residuals between observations and the model near the primary minimum are presented on the lower panel. Dashed vertical lines indicate the beginning, middle, and the end of the eclipse.}{5856-f5.eps}{Differential $BVR$ light curves of GSC 3889-0202 (VAR--COMP, diamonds) around secondary minimum and shifted C3 star (C3--COMP, crosses). Dashed vertical lines indicate the middle of the secondary eclipse.}
\IBVSfigKey{5856-f4.eps}{GSC 3889-0202}{light curve}
\IBVSfigKey{5856-f5.eps}{GSC 3889-0202}{light curve}
\IBVSfig{5.6cm}{5856-f6.eps}{Power spectrum of GSC 3889-0202 Rozhen data after subtracting the synthetic light curve from the data.}
\IBVSfigKey{5856-f6.eps}{GSC 3889-0202}{periodogram}


\references

Bessell, M., S., 1990, {\it PASP}, {\bf 102}, 1181

Castelli, F., Kurucz, R., 2003, {\it IAU Symp.}, {\bf 210}, \nobibcode 20
\BIBCODE{2003IAUS..210P.A20C}

Everett, M., Howell, S., 2001, {\it PASP}, {\bf 113}, 1428

Gray, R., Corbally, C., 1994, {\it AJ}, {\bf 107}, 742

Pr\v{s}a, A., Zwitter, T. 2005, {\it ApJ} {\bf 628}, 426

Wozniak, P., Vestrand, W., Akerlof, C., et al., 2004, {\it AJ}, {\bf 127}, 2436

\endreferences

\IBVSedata{5856-t5.txt}
\IBVSdataKey{5856-t5.txt}{GSC 3889-0202}{photometry}
\IBVSedata{5856-t6.txt}
\IBVSdataKey{5856-t6.txt}{GSC 3889-0202}{photometry}
\IBVSedata{5856-t7.txt}
\IBVSdataKey{5856-t7.txt}{GSC 3889-0202}{photometry}
\IBVSedata{5856-t8.txt}
\IBVSdataKey{5856-t8.txt}{GSC 3889-0202}{radial velocity}
\IBVSedata{5856-t9.txt}
\IBVSdataKey{5856-t9.txt}{GSC 3889-0202}{spectrum}
\IBVSedata{5856-t10.txt}
\IBVSdataKey{5856-t10.txt}{GSC 3889-0202}{spectrum}
\IBVSedata{5856-t11.txt}
\IBVSdataKey{5856-t11.txt}{GSC 3889-0202}{spectrum}

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