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\IBVShead{5883}{7 April 2009}

\IBVStitletl{Short-Period Oscillations in the Algol-type Systems III:}{ Newly Discovered Variable GSC~4588-0883}

\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 4588-0883}{TYC 4588-883-1}
\IBVStyp{ oEA }
\IBVSkey{eclipsing binaries, oscillating variables, photometry, spectroscopy}
\IBVSabs{On the basis of the NSVS data search the star GSC 4588-0883 was}
\IBVSabs{discovered as a new Algol-type system. According to Rozhen CCD}
\IBVSabs{observations orbital period of the star is P_orb=3.25855 days }
\IBVSabs{and amplitude of primary minimum is A_R=0.62 mag.}
\IBVSabs{Short-period oscillations with amplitude up to 0.015 mag in R and}
\IBVSabs{main periodicity in the interval 71 div 78 minutes were found.}
\IBVSabs{Preliminary physical parameters of the system are computed.}


\begintext

GSC 4588-0883 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 $P \simeq 3.2582$ days, amplitude of primary minimum $A_R > 0.65$ mag, and the magnitude in maximum $R'_{\rm max} \simeq 11.67$ mag. The astrometric and photometric data for the star (Table~1) are taken from NOMAD catalogue (Zacharias et al., 2004).

The CCD photometry (in $BVR$ bands) of GSC 4588-0883 was carried out with the 60cm Cassegrain telescope at NAO Rozhen, equipped with the CCD camera FLI PL09000 (3056$\times$3056, 12$\mu$ pixel), and Bessell (1990) standard $UBVRI$ filters. The standard IRAF procedures were used for the reduction of the photometric data. Using the method of Everett and Howell (2001) six stars with $\sigma < 0.005$ mag in all $R$ band observations (Table~1) were selected to create an ensemble standard star.

The NSVS and Rozhen's light curves of GSC 4588-0883 are shown on Fig.~2. The light curves for 6 nights, obtained in $R$ band are shown in Fig.~4 and Fig.~5. Short-period oscillations with a peak-to-peak amplitude of up to 0.015 mag in $R$ (Table~2) were detected. The oscillations are smaller than in the previous discovered stars \hbox{GSC 4550-1408} and GSC 3889-0202 (Dimitrov et al., 2008a,b). The oscillations are present at the primary and the secondary minima also. A preliminary periodogram analysis (Fig.~6) of the data shows a main periodicity in the interval $71 \div 78$ minutes.

Spectral observations of GSC 4588-0883 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 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\'sa \& Zwitter, 2005). The spectral types of the components were determined using Strai\v{z}ys \& Kuriliene (1981) calibration (Table~4).
 
The new ephemeris were computed using both Rozhen and NSVS data:

\begin{equation}
HJD(\mbox{MinI})  =  2451274.021(\pm 0.005) + 3.25855(\pm 0.00009) E
\end{equation} 

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

\centerline{Table 1. Data for the variable, and standard stars used in the CCD photometry}
\vskip 3mm
\begin{center}
\begin{tabular}{ccccccc}
\hline
ID   & Name  & RA (J2000) & DEC (J2000)  & $V$ & $B-V$ & $V-R$ \\
\hline
VAR & GSC 4588-0883 & 19\hr 27\mm 53\fsec70 & +77\deg 17\arcm 41\farcs8 & 11.32 & 0.50 & 0.34 \\
C1  & GSC 4588-0579 & 19\hr 25\mm 59\fsec69 & +77\deg 25\arcm 47\farcs9 & 11.38 & 0.46 & 0.31 \\
C2  & GSC 4588-2368 & 19\hr 26\mm 12\fsec00 & +77\deg 27\arcm 25\farcs9 & 12.26 & 1.02 & 0.97 \\
C3  & GSC 4588-0521 & 19\hr 28\mm 07\fsec31 & +77\deg 20\arcm 51\farcs4 & 12.35 & 0.92 & 0.88 \\
C4  & GSC 4588-0164 & 19\hr 30\mm 24\fsec86 & +77\deg 17\arcm 21\farcs8 & 12.20 & 1.01 & 0.63 \\
C5  & GSC 4588-0781 & 19\hr 27\mm 30\fsec51 & +77\deg 26\arcm 49\farcs5 & 13.15 & 0.41 & 0.31 \\
C6  & GSC 4588-1313 & 19\hr 26\mm 32\fsec13 & +77\deg 25\arcm 42\farcs9 & 13.02 & 0.54 & 0.32 \\
\hline
\end{tabular}
\end{center}


\centerline{Table 2. Observational runs of GSC 4588-0883}
\vskip 3mm
\begin{small}
\begin{center}
\begin{tabular}{ccccrccc}
\hline
Date   &  HJD(start)  &  Length & Filter   & Exp. [s] &  N  & Phase & $A_R$max(osc.) \\
\hline
02.09.2008  &  2454712.24749  &  04\hr 40\mm  &  $R$  & 120  &  120  &  0.14 - 0.20  &  0.015  \\ 
03.09.2008  &  2454713.42091  &  03\hr 57\mm  &  $R$  & 120  &  131  &  0.50 - 0.55  &  0.010  \\ 
04.09.2008  &  2454714.40448  &  05\hr 24\mm  &  $R$  & 120  &  128  &  0.80 - 0.87  &  0.015  \\ 
05.09.2008  &  2454715.53156  &  01\hr 51\mm  &  $R$  & 120  &   45  &  0.15 - 0.17  &  0.012  \\ 
08.09.2008  &  2454718.25881  &  08\hr 33\mm  &  $R$  & 120  &  202  &  0.98 - 0.09  &  0.015  \\ 
03.10.2008  &  2454743.45837  &  04\hr 18\mm  &  $BVR$ & 3$\times$120 & 38,38,38 & 0.72 - 0.77 & 0.012  \\ 
31.10.2008  &  2454771.18693  &  00\hr 42\mm  &  $R$  & 120  &   20  &  0.23 - 0.24  &    \\ 
01.11.2008  &  2454772.35613  &  03\hr 18\mm  &  $R$  & 120  &   89  &  0.59 - 0.63  &  0.015  \\ 
02.11.2008  &  2454773.39219  &  01\hr 25\mm  &  $R$  & 120  &   38  &  0.59 - 0.63  &    \\ 
04.11.2008  &  2454775.20502  &  03\hr 05\mm  &  $BVR$ & 3$\times$120 & 26,23,23 &  0.46 - 0.50  & $< 0.01$ \\ 
\hline
\end{tabular}
\end{center}
\end{small}


\centerline{Table 3. Rozhen spectra of GSC 4588-0883}
\vskip 3mm
\begin{center}
\begin{tabular}{ccccr@{$\pm$}lccc}
\hline
  Date     &  HJD(mid)   & S/N & Exp. & \multicolumn{2}{c}{RV}  &  Region & Phase \\
               &         &       &   [s]  &  \multicolumn{2}{c}{[kms$^{-1}$]} &  [\AA{}]&  \\
\hline
15.10.2008 & 2454755.4238 & 36 & 1800 & $-$64.18 & 1.39 & 4400 - 4600 & 0.390\\
15.10.2008 & 2454755.4468 & 47 & 1800 & $-$61.35 & 2.58 & 4800 - 5000 & 0.397\\
15.10.2008 & 2454755.4696 & 56 & 1800 & $-$49.87 & 2.18 & 6500 - 6700 & 0.404\\
16.10.2008 & 2454756.2574 & 44 & 1800 & $-$17.52 & 1.50 & 4400 - 4600 & 0.646\\
16.10.2008 & 2454756.2785 & 41 & 1800 & $-$16.71 & 1.12 & 4400 - 4600 & 0.652\\
16.10.2008 & 2454756.3016 & 50 & 1800 & $-$12.89 & 3.01 & 4800 - 5000 & 0.660\\
16.10.2008 & 2454756.3227 & 54 & 1800 & $-$12.61 & 2.03 & 4800 - 5000 & 0.666\\
16.10.2008 & 2454756.3454 & 60 & 1800 & $-$11.10 & 2.55 & 6500 - 6700 & 0.673\\
16.10.2008 & 2454756.3665 & 61 & 1800 & $-$13.14 & 2.05 & 6500 - 6700 & 0.679\\
\hline
\end{tabular}
\end{center}

\centerline{Table 4. Preliminary physical parameters of GSC 4588-0883 binary system}
\vskip 3mm
\begin{center}
\begin{tabular}{cccc}
\hline
 \multicolumn{2}{c}{Parameter}     & Primary star   & Secondary star \\
\hline
$T_{\mbox{eff}}$ & [K] & 7650 & 4100 \\
$\log g$ & & 3.9 & 3.2\\
Spectral type & & A9 IV & K4 III \\
$M_{\rm S}$/M$_{\rm P}$ & &\multicolumn{2}{c}{0.16} \\
$K_{\rm P}$ & [kms$^{-1}$] & \multicolumn{2}{c}{63.0} \\
$\gamma$ & [kms$^{-1}$] & \multicolumn{2}{c}{$-$42.0} \\
$i$   & [deg]  &  \multicolumn{2}{c}{78.5} \\
$v \sin i$ & [kms$^{-1}$] &  \multicolumn{2}{c}{$\sim 60$} \\ 
\hline
\end{tabular}
\end{center}



\IBVSfig{10.0cm}{5883-f1.eps}{Field of the eclipsing binary GSC 4588-0883.}
\IBVSfigKey{5883-f1.eps}{GSC 4588-0883}{finding chart}

\IBVS2fig{7.0cm}{5883-f2.eps}{Light curves of GSC 4588-0883. Upper panel - NSVS data, lower panel - Rozhen R data (dots) and model (solid line).}{5883-f3.eps}{Rozhen combined spectra (thin line) of GSC 4588-0883  and the best synthetic spectra (thick~line).}
\IBVSfigKey{5883-f2.eps}{GSC 4588-0883}{light curve}
\IBVSfigKey{5883-f3.eps}{GSC 4588-0883}{spectrum}

\newpage
\IBVS2fig{7.0cm}{5883-f4.eps}{R light curves of GSC 4588-0883 (diamonds) and C1 standard star (crosses).}{5883-f5.eps}{Residuals between observations and the model near the primary and secondary minima (diamonds) and shifted C1 standard (crosses). Dashed vertical lines indicate the middle and the end of the eclipses.}
\IBVSfigKey{5883-f4.eps}{GSC 4588-0883}{light curve}
\IBVSfigKey{5883-f5.eps}{GSC 4588-0883}{light curve}

\IBVSfig{4.5cm}{5883-f6.eps}{Power spectrum of GSC 4588-0883 Rozhen data after subtracting the synthetic light curve.}
\IBVSfigKey{5883-f6.eps}{GSC 4588-0883}{periodogram}


\references

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

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

Dimitrov, D., Kraicheva, Z., Popov, V., 2008a, {\it IBVS}, No 5842

Dimitrov, D., Kraicheva, Z., Popov, V., 2008b, {\it IBVS}, No 5856

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

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

Pr\'sa, A., Zwitter, T., 2005, {\it ApJ}, {\bf 628}, 426

Strai\v{z}ys, V., Kuriliene, G., 1981, {\it ApSS}, {\bf 80}, 353

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

Zacharias, N., Monet, D., Levine, S. et al., 2004, {\it AAS}, {\bf 205}, 4815

\endreferences

\IBVSedata{5883-t5.txt}
\IBVSdataKey{5883-t5.txt}{GSC 4588-0883}{photometry}
\IBVSedata{5883-t6.txt}
\IBVSdataKey{5883-t6.txt}{GSC 4588-0883}{photometry}
\IBVSedata{5883-t7.txt}
\IBVSdataKey{5883-t7.txt}{GSC 4588-0883}{photometry}
\IBVSedata{5883-t8.txt}
\IBVSdataKey{5883-t8.txt}{GSC 4588-0883}{radial velocity}
\IBVSedata{5883-t9.txt}
\IBVSdataKey{5883-t9.txt}{GSC 4588-0883}{spectrum}
\IBVSedata{5883-t10.txt}
\IBVSdataKey{5883-t10.txt}{GSC 4588-0883}{spectrum}
\IBVSedata{5883-t11.txt}
\IBVSdataKey{5883-t11.txt}{GSC 4588-0883}{spectrum}

\end{document}

