\documentstyle[twoside,epsf]{article}\input ibvs2.sty
\input ibvse.sty

\begin{document}

\IBVShead{6136}{15 April 2015}
\IBVStitle{A variable star in the field around TrES-4}
\IBVSauth{ Gaynullina, E.R.; Serebryanskiy, A.V.; Khalikova, A.V.;  Karimov, R.G.}
\IBVSinsto{Ulugh Beg Astronomical Institute, Astronomicheskaya str., 33, 100072 Tashkent, Uzbekistan\\
email: alex@astrin.uz, evelina@astrin.uz}

\SIMBADobj{USNO-A2.0 1200-08721202}

\begintext

Transits of exoplanets were occasionally observed on Maidanak 
Observatory of Uzbekistan in the period from 2010 to 2013 using Zeiss-600 telescope equipped with FLI IMG1001E (in 2010) and
FLI MicroLine (2012-2013) with FoV equal to $11\farcm7 \times 11\farcm7$. Observations of exoplanet host star TrES-4 (RA$_{2000}$=17\hr53\mm13\fsec058;  
DEC$_{2000}$=+37\deg12\arcm42\farcs36) was performed in 2010 in filter Cousins R and in 2012 and 2013 using filter Bessell R. 
We also provide with additional information on observation in Table~\ref{table2}: start and end times of 
observation (at middle time of exposure), the exposure time, air mass for the first and the last frames 
for each night and average Full Width on Half Maximum (FWHM) of a star profile. In 2012 the air mass initially decreased 
down to 1.001 and then increased again.

\begin{table}[h!]
\caption{Observational info} 
\centering 
\begin{tabular}{cccccc} 
\hline 
 Date (UTC)    &  Start time        &  End time        &  Exp. time  & Air mass        &  FWHM    \\
               &  (UTC)             &  (UTC)           & & & \\
               &   hh:mm:ss         &  hh:mm:ss        &      sec        & start : end    &  arcsec  \\
\hline 
Aug 30, 2010   &  15:11:37          &  20:41:04        &  30             & 1.003 : 2.489  &  2.02    \\ 
July 23, 2012  &  15:58:21          &  21:10:03        &  60             & 1.039 : 1.415  &  2.00    \\
June 12, 2013  &  16:32:58          &  19:15:26        &  40, 60         & 1.414 : 1.012  &  1.73    \\
\hline
\end{tabular}
\label{table2}
\end{table}


\begin{table}[h!]
\caption{Mode parameters} 
\centering
\begin{tabular}{cccccc}
\hline 
 Date  & Frequency    &  $\sigma_F$  & Amplitude   & $\sigma_A$   &  SNR  \\
 & c/d & c/d & mmag & mmag & \\
\hline
2010   &  11.802     &      -        & 19.9      &    0.4     &  18.4   \\ 
\hline
2012   &  11.781     &      -        & 19.8      &    0.3     &  18.8   \\
\hline
2013   &  11.511     &      -        & 19.5      &    0.5     &  42.8   \\
\hline
All    & 11.805823   &   0.000005    & 19.8      &    0.2     &  28.2  \\
\hline
\end{tabular}
\label{table3}
\end{table}


\IBVSfig{8cm}{6136-f1.eps}{Image taken on July 23, 2012. TrES-4, the new variable star (Var) and 
comparison stars are marked. North is up and East is to the left.}
\IBVSfigKey{6136-f1.eps}{USNO-A2.0 1200-08721202}{finding chart}


\IBVSfig{10cm}{6136-f2.eps}{The light curves of the new variable star.}
\IBVSfigKey{6136-f2.eps}{USNO-A2.0 1200-08721202}{light curve}



Basic reduction of the frames was done using standard IRAF\IBVSfm~software.  
We did the aperture photometry for all stars which can be used as the comparison stars. In the end, 
we selected 7 stars for further analyses. In Figure~1 we show our field of view in 2012 and mark the comparison 
stars as $Sn$, $n=1,2...$. In 2010 and 2013 we used $S1$, $S2$ and $S3$ comparison stars and in 2012 we used 
all seven stars. One star marked as $Var$ has shown variability with an amplitude of $\approx 0.04$ mag.
Because we used different comparison stars, nightly average values were subtracted from each light curve.
Neither linear nor parabolic trends were removed and no differential extinction corrections were applied.
We plot the light curves of the variable star in Figure~2. The final light curves contain 509
data points in 2010, 300 data points in 2012 and 147 data points in 2013. The {\tt 6136-t3.txt} file containing the photometry is available online.

\IBVSfoot{IRAF is distributed 
by the NOAO, which are  operated by the AURA, Inc., under cooperative agreement with the NSF}



This $Var$ star is not included in any of catalogues. We did not find any reference on it in the 
publications devoted to TrES-4. But we have found the short report (DeCoster et al., 2011) where the 
authors wrote about searching for variable stars in the archival mid-infrared data (4.5-micron) 
from the Spitzer Space Telescope. They found one star in the TrES-4 field that displayed periodic
variability (P = 0.082 days) when phase-folded.



\IBVSfig{10cm}{6136-f3.eps}{The spectral windows. }
\IBVSfigKey{6136-f3.eps}{USNO-A2.0 1200-08721202}{periodogram}

For the power spectral analysis of the light curves the FAMIAS software package (Zima, 2008) was used. 
Figure~3 presents the spectral windows. The width of the smoothing window for noise level estimation
(box size) was set to 16 c/d. Amplitudes in power spectra of several modes exceeded $4\sigma$ for
each light curve. Only one mode was present for all light curves. We show the results in Table~
\ref{table3}. The errors of the frequency estimation for individual light curve are not presented
due to the low resolution of power spectra which caused instability of frequencies.
The spectral analyses of the total light curve (for all 3 years data points) gives the period of
P=0.085 days which is very close to that reported in (DeCoster et al., 2011). This suggests that we are 
probably dealing with the same star.

Considering the amplitude and period of oscillations we tend to assume that this variable star could 
belong to $\delta$ Sct type.



{\bf Acknowledgements:} The authors are supported by Fundamental Research Grants FA-F02-F027 and
FA-F02-F028 of the Uzbek Academy of Sciences. We thank the observers Khafizov B., 
Fayziev S. and Parmonov O. We also thank the anonymous referee for important 
suggestions and comments.

\references

DeCoster, R., Piper, P., Thomas, B. et al., 2011, {\it Bulletin of the American Astronomical 
Society}, {\bf 43}, 342 \BIBCODE{2011AAS...21734203D}

Zima, W., 2008, {\it Communications in Asteroseismology}, {\bf 155}, 17

\endreferences

\IBVSedata{6136-t3.txt}
\IBVSdataKey{6136-t3.txt}{USNO-A2.0 1200-08721202}{photometry}

\end{document}

