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\IBVShead{6040}{24 November 2012}

\IBVStitle{A new variable star: GSC 02936-00267}
 
\IBVSauth{Zhang, Y.P.$^1$; Yan, K.Z.$^1$; Fu, J.N.$^1$; Bai, Y.$^1$; Zhang, C.$^2$; Zha, Q.$^1$}

\IBVSinst{Department of Astronomy, Beijing Normal University, Beijing 100875, China. e-mail: zhangyp@bnu.edu.cn}
\IBVSinst{National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China}

\SIMBADobj{GSC 02936-00267}

\IBVSkey{new variable star, GSC 02936-00267, delta Scuti variable}

\IBVSabs{We discovered the variability of GSC 02936-00267 }
\IBVSabs{during our observation run on January 15, 2008. In order to }
\IBVSabs{determine the spectral type and the }
\IBVSabs{period, we made time-series photometric }
\IBVSabs{observations in Johnson B, V, R bands for seven nights between }
\IBVSabs{January 2008 and January 2011 and low-resolution }
\IBVSabs{spectroscopic observations in November 2008. Based on the }
\IBVSabs{observational data, we classified GSC 02936-00267 as a delta Scuti }
\IBVSabs{type variable and derived its pulsation period and }
\IBVSabs{time of maximum.}
\begintext

During the observations of the eclipsing binary GSC 2936-0478 (Yang et al. 2005) with the 85-cm telescope at Xinglong Station of National Astronomical Observatories of China on January 15, 2008, a new variable star was discovered in the field of view. The new variable star was identified to be GSC 02936-00267 according to the GSC 1 catalog (Morrison et al. 2001), which was named as GSC N8QG000518 in GSC 2.3 (Lasker et al. 2008) and 06361162+4200575 in 2MASS Point Source Catalog. The coordinates of the star is R.A. = 06\hr 36\mm 11\fsec 61, DEC=+42\deg 00\arcm 58\farcs 7 (epoch=J2000), $V$= 13\fmm 58.

Time-series photometric observations were made for the field of GSC 02936-00267 with the 85-cm reflecting telescope at Xinglong station. A PI $1024\times1024$ BFT CCD camera was mounted at the primary focus of the telescope (Zhou et al. 2009). Each pixel of the CCD camera scales $0.96''$ on the sky, leading to a field of view of $16.5' \times 16.5'$. The CCD camera was equipped with a set of standard Johnson-Cousins-Bessell $UBVRI$ filters. Observation dates, available frames and exposure time in the different filters are listed in Table 1.

\begin{table}[!ht]
\small
\centerline{{\bf Table\,1.} Observation dates, available frames and exposure time in the different filters}
\begin{center}
\begin{tabular}{ccc}
\hline
   Observation date    & Filter  & Filter \\
                       & /available frames & /exposure time \\
\hline
Jan. 15, 2008 & $B$/225, $V$/225 & $B$/80\,s, $V$/45\,s \\
Dec. 08, 2010 & $R$/112, $V$/112 & $V$/80\,s, $R$/60\,s \\
Dec. 11, 2010 & $R$/155, $V$/148 & $V$/80\,s, $R$/60\,s \\
Dec. 13, 2010 & $R$/66, $V$/71 & $V$/80\,s, $R$/60\,s \\
Jan. 21, 2011 & $R$/140, $V$/140 & $V$/90\,s, $R$/50\,s \\
Jan. 22, 2011 & $R$/136, $V$/138 & $V$/90\,s, $R$/50\,s \\
Jan. 26, 2011 & $R$/158, $V$/158 & $V$/90\,s, $R$/50\,s \\
\hline
\end{tabular}
\end{center}
\end{table}

Four reference stars and one check star, as shown in Figure 1, were chosen to obtain differential photometry for the target star. Names, coordinates and magnitudes of these stars are listed in Table 2.

We used the software package IRAF\footnote{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.} for data reduction and aperture photometry. The same apertures were used for the 6 stars and light curves of $m_{Chk}-(m_{Ref1} + m_{Ref2} + m_{Ref3} + m_{Ref4})/4$ and $m_{Obj}-(m_{Ref1} + m_{Ref2} + m_{Ref3} + m_{Ref4})/4$ were calculated, where m denotes magnitude. By choosing the light curves of $m_{Chk}-(m_{Ref1} + m_{Ref2} + m_{Ref3} + m_{Ref4})/4$ which have the smallest value of dispersion, we could determine the best aperture for photometry and obtain light curves of the target star and the check star relative to the reference stars. Light curves of the target star in $V$ are shown in Figure 2.

\begin{table}[!ht]
\small
\centerline{{\bf Table\,2.} Names, coordinates and magnitudes of the reference stars and check star}
\begin{center}
\begin{tabular}{ccccc}
\hline
  Number & Name & ${\alpha}_{2000.0}$ & ${\delta}_{2000.0}$ & Magnitude ($V$) \\
         &      & hh:mm:ss         & \hspace{4mm} $\deg$ \hspace{1mm} $^{\prime}$ \hspace{1mm} $^{\prime \prime}$ &  \\
\hline
Ref1 & GSC 02936-00201 & 06 36 05.62 & +41 59 59.1 & 13.86 \\
Ref2 & GSC 02936-00284 & 06 35 45.11 & +42 01 26.4 & 13.56 \\
Ref3 & GSC 02936-00466 & 06 35 21.54 & +42 04 09.8 & 12.85 \\
Ref4 & GSC 02936-00460 & 06 36 23.30 & +42 04 00.1 & 12.67 \\
Chk1 & GSC 02936-00417 & 06 35 56.05 & +42 05 41.9 & 13.24 \\
\hline
\end{tabular}
\end{center}
\end{table}

\IBVSfig{10.5cm}{6040-f1.eps}{Observed field of GSC 02936-00267 (Obj). The reference stars (Ref) and check star (Chk) are also marked. The size of the FOV is $16.5' \times 12'$.}
\IBVSfigKey{6040-f1.eps}{GSC 02936-00267}{finding chart}

\IBVSfig{20cm}{6040-f2.eps}{Light curves of GSC 02936-00267 in $V$}
\IBVSfigKey{6040-f2.eps}{GSC 02936-00267}{light curve}

On 20 November 2011, the OMR low-dispersion spectrograph mounted on the 2.16-m telescope at Xinglong station was used to take a spectrum of GSC 02936-00267. The slit width was $2\farcs 2$. The reciprocal linear dispersion of the grating is 200 \AA/mm or 9.36 \AA/pixel. The spectral range is 400 nm --- 800 nm. The central wavelength is 600 nm. The spectrum is shown in Figure 3.

\IBVSfig{10.5cm}{6040-f3.eps}{Low-dispersion spectrum of GSC 02936-00267. The y axis is the flux in ${\mathrm erg\ s^{-1} cm^{-2} \AA^{-1}}$.}
\IBVSfigKey{6040-f3.eps}{GSC 02936-00267}{spectrum} 

From the spectrum of the star GSC 02936-00267, we identified the spectral lines of ${\mathrm H_\alpha, H_\beta, H_\gamma, H_\delta}$ and the spectral line of sodium at 589~nm. According to the reference of Pickles Atlas (Pickles 1998), we identified the spectral type of GSC 02936-00267 as F2V based on the ratio of depths of the spectral lines of ${\mathrm H_\alpha}$ and of sodium at 589~nm. We note that there is a strong emission line with a central wavelength of 572.5~nm and full width at half maxium of around 6.5~nm. Since there was a fainter star very close to GSC 02936-00267 in the slit during the observations, we suspect that the emmission line was created by the fainter star whose spectral type is unknown. This needs to be confirmed with spectroscopic observations for the two stars respectively with larger-aperture telescopes.

The software package Period04 (Lenz \& Breger 2005) was used to analyze pulsation periods of GSC 02936-00267. The results ot the analysis are as follows:
\begin{description}
 \item Main frequency $(f_1)= 7.488423~{\rm d}^{-1}$
 \item Amplitude of the main frequency $(A)$ $=0\fmm 010 \pm 0.001~{\mathrm mag}$
 \item $T_{\rm Max} = {\rm HJD}~2454480.99916 + 0\fday133539(5) \times E$ .
\end{description}


According to the pulsation frequency and the spectrum of GSC 02936-00267, we classify it as a $\delta$ Scuti type variable.

Since there is a faint neighboring star ($V=13\fmm 58$) very close to GSC 02936-00267, and because the amplitude of pulsation is small ($A\sim 0\fmm 01$), more time-series photometric data and spectroscopic observations are needed to confirm the spectral type classification and check the pulsation period.

Acknowledgments:
We acknowledge the support from National Natural Science Foundation of China (NSFC), through the Grants 10778601 and U1231202. The research is partially supported by National Basic Research Program of China (973 Program 2013CB834900) and the fundamental Research Funds for the Central Universities.

\references

Lasker, B.M., Lattanzi, M.G., McLean, B.J. et al. 2008, {\it AJ}, {\bf 136}, 735

Lenz, P., and Breger, M. 2005, {\it Commun. Asteroseismol.}, {\bf 146}, 53

Morrison, J.E., Roeser, S., McLean B., Bucciarelli, B., Lasker, B. 2001, {\it AJ}, {\bf 121}, 1752

Pickles, A.J. 1998, {\it PASP}, {\bf 110}, 863

Yang, Y.G., Qian, S.B., Gonzalez-Rojas, D.J. and Yuan, J.Z. 2005, {\it ApSS}, {\bf 300}, 337

Zhou, A.Y., Jiang, X.J., Zhang, Y.P., Wei, J.Y. 2009, {\it Res. Astron. Astrophys.}, {\bf 9}, 349

\endreferences

\IBVSedata{6040-t3.txt}
\IBVSdataKey{6040-t3.txt}{GSC 02936-00267}{photometry}
\IBVSedata{6040-t4.txt}
\IBVSdataKey{6040-t4.txt}{GSC 02936-00267}{spectrum}

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