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\IBVSheadDOI{63}{6246}{20 July 2018}

\IBVStitle{Photometry of GS UM\lowercase{a}: a suspected \boldmath{$\delta$} Scuti variable}

\IBVSauth{Kahraman Ali\c{c}avu\c{s}, F.; Raheem, A.; \c{C}oban G. \c{C}.; Tambulut, E. M.; G\"{o}g\"{u}lter, \"{U}.;BA\c{S}, L.; \c{C}evirici, B.}

\IBVSinsto{Faculty of Sciences and Arts, Physics Department, \c{C}anakkale Onsekiz Mart University, 17100, \c{C}anakkale, Turkey \newline e-mail: filizkahraman01@gmail.com}

\SIMBADobj{GS UMa}

\IBVSkey{variables, CCD photometry, Delta Scuti stars}

\IBVStyp{ DSCT }

\IBVSabs{We present the time series analysis of GS UMa. GS UMa is a suspected $\delta$ Scuti variable with a primary frequency of 6.0987 d$^{-1}$.}


\begintext

$\delta$ Scuti stars are one of the most known pulsating variables which oscillate in radial and non-radial 
pressure, gravity and mixed modes mostly in a frequency ranges of 5$-$50 d$^{-1}$ (Breger, 2000). Thanks to the space missions 
({\sl Kepler}, CoRoT, MOST), many new $\delta$ Scuti variables have been discovered. These discoveries have uncovered
new problems about $\delta$ Scuti stars. One of the problems concerns the borders of the $\delta$ Scuti instability strip. 
Uytterhoeven et al.~(2011) showed that there are many $\delta$ Scuti variables located outside their own instability strip. 
According to the theory, it is not expected to detect such variables beyond the borders. 


GS UMa (V=8\fmm66, HIP\,51361, RA\,=\,10\hr 29\mm 26\fsec8, DEC\,=\ +39\deg 46\arcm 08\farcs5) is a poorly classified $\delta$ Scuti variable. Its variability was first found by Duerbeck (1997) using the {\sc Hipparcos} data. The star was defined as a suspect $\delta$ Scuti star by Kahraman Ali{\c c}avu{\c s} et al.~(2017). They carried out a detailed spectroscopic analysis of the star and derived the atmospheric parameters (effective temperature $T_{\rm eff}$, surface gravity $\log g$, microturbulent velocity $\xi$), projected rotational velocity, and the chemical abundances of the variable. As a result of their analysis, they showed that the star is located outside the instability strip of $\delta$ Scuti stars. Therefore, in this study, we focus on the photometric observations of GS UMa to reveal its variability type. 


\begin{table}[h]
\begin{center}
\caption{Information of the comparison (C1) and the check (C2) stars.}
\begin{tabular}{ccccc}
\hline
ID   & Name              & RA (J2000) & DEC (J2000)     & V (mag)\\\hline
C1   & GSC 3002$-$00989  & 10\hr 29\mm 15\fsec5 & +39$^{o}$ 45\arcm 00\farcs4 & 9.89\\
C2   & GSC 3002$-$00097  & 10\hr 28\mm 58\fsec1 & +39$^{o}$ 40\arcm 01\farcs0 & 9.30\\ 
\hline
\end{tabular}
\end{center}
\end{table}



Photometric observations of GS UMa were carried out at the \c{C}anakkale Onsekiz Mart University Observatory 
with the Apogee ALTA U47 CCD mounted on the 30\,cm Cassegrain-Schmidt telescope. The photometric data was obtained with 
Johnson $B$ and $V$ filters on 4, 12, 19, 26, and 28 April 2018. About 25 hours of data was taken during the observation period. 
From the observations, the stars which do not exhibit any significant light variation, were selected to be comparison and check stars. 
Information of the comparison and check stars used are given in Table\,1.
The basic image reduction steps (bias, dark, and flat correction) were performed by using the C-Munipack\footnote{\tt http://c-munipack.sourceforge.net/} software.


\IBVSfig{8cm}{6246-f1.ps}{Power spectrum of GS UMa. Solid horizontal line represents the significance limit.}


The observed light curves were analysed by using the Period04 program (Lenz \& Breger 2005) to derive the pulsation period and amplitude of the star. 
As a result of this analysis, a significant pulsation frequency of 6.0987 d$^{-1}$ with signal-to-noise (S/N) 
level higher than the significance limit (S/N\,$\geq$\,4, Breger et al. 1993) and with 46.35 mmag pulsation amplitude in $V$ filter 
was obtained. Furthermore, we detected a frequency value lower than 5 d$^{-1}$. However, its S/N level is lower than the 
significance limit. The existence of this frequency should be checked with new long-term observations. Additionally, we used the SuperWASP data\footnote{\tt https://wasp.cerit-sc.cz/form} for the frequency analysis. In this analysis,
we determined three significant frequencies. The obtained frequencies can be found in Table\,2. The power spectrum and 
the comparison of the observed light curves with the calculated ones are shown in Fig.\,1 and Fig.\,2, respectively. 


\IBVSfig{7cm}{6246-f2.ps}{Comparison of the observed $B$ (left panel) and $V$ (right panel) light curves of GS UMa with the calculated light curves (solid lines).}

We calculated the pulsation constant ($Q$) value of the star by utilizing the below equation given by Petersen \& J\o{}rgensen (1972).

\begin{displaymath}
\log Q = -6.456+0.5\log g+0.1M_{\rm Bol}+\log T_{\rm eff}+\log P
\end{displaymath}
 
The $T_{\rm eff}$ and $\log g$ values were taken from Kahraman Ali{\c c}avu{\c s} et al.~(2017). $M_{\mathrm Bol}$ 
was calculated using the bolometric correction value which was taken from Cox et al.~(2000) and the \textit{Gaia} parallax (Gaia Collaboration et al. 2016). As a result of this calculation,
we determined the $Q$ value to be $0\fday069\pm0.012$. This value is out of range of $Q$ for $\delta$ Scuti stars 
according to the study of Antonello \& Pastori (1981). However, it should be noticed that a limited number of stars were used in this study.

GS UMa is located beyond to the red border of $\delta$ Scuti and $\gamma$ Doradus instability strip (Kahraman Ali{\c c}avu{\c s} et al., 2017).
According to our frequency analysis results, the star shows $\delta$ Scuti-type pulsation. However, we also detected a frequency lower than 
5 d$^{-1}$. This frequency is in the range of $\gamma$ Doradus stars' pulsation frequency interval. In addition, it is shown that a large 
majority of $\delta$ Scuti stars ($\sim$\,98\%) in the {\sl Kepler} field show low frequencies (Balona, 2018). A most recent explanation of these low 
frequencies was explained by interaction between oscillation and convection (Xiong et al., 2016). Therefore, GS UMa simply might be a 
$\delta$ Scuti star exhibiting low frequency pulsation. However, to reveal this feature the star needs more high quality observations. \\


\begin{table}
\begin{center}
\caption{Frequencies detected in GS UMa.}
\begin{tabular}{llccc}\hline
Filter   &Parameter        & Frequency  	       & Amplitude      & S/N\\
         &        & (d$^{-1}$)          & (mmag)          &    \\
\hline \\
$B$      & f$_{1}$      & 6.0987$\pm$0.0014   & 38.76$\pm$1.62  & 24\\
$V$      & f$_{1}$      &6.0987$\pm$0.0013    & 46.35$\pm$0.99  & 18\\
SuperWASP&f$_{1}$      & 6.0972$\pm$0.0000   & 41.99$\pm$0.34  & 34\\
SuperWASP&f$_{2}=2$f$_{1}$  & 12.1944$\pm$0.0000  & 11.29$\pm$0.37  & 11\\
SuperWASP&f$_{3}$      & 5.0120$\pm$0.0056   & 6.68$\pm$0.61   & 5\\

\hline
\end{tabular}
\end{center}
\end{table}

{\bf Acknowledgements:} 
The authors would like to thank the reviewer for useful comments
and suggestions. This research was carried out as a part of the Practical Astronomy course (14FZK416 / FZK466) of Physics Department of 
\c{C}anakkale Onsekiz Mart University (Turkey). The lecturer FKA thanks her students for their enthusiasm in the study.
This paper makes use of data from the first public release of the WASP data (Butters et al. 2010) as provided 
by the WASP consortium and services at the NASA Exoplanet Archive, which is operated by the California Institute 
of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program.
This work has made use of data from 
the European Space Agency (ESA) mission Gaia ({\tt http://www.cosmos.esa.int/gaia}), processed by the Gaia Data Processing 
and Analysis Consortium (DPAC, {\tt http://www.cosmos.esa.int/web/gaia/dpac/consortium}). Funding for the DPAC has been 
provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. 
This research has made use of the SIMBAD data base, operated at CDS, 
Strasbourg, France. 

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