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\begin{document}

\IBVSheadDOI{63}{6229}{21 December 2017}

\IBVStitletl{Discovery of the Blazhko effect in V1065 A\lowercase{ql}, C\lowercase{ze}V980,}{ FI S\lowercase{ge}, and C\lowercase{ze}V1242}


\IBVSauth{Skarka, M.$^{1,2,3}$; Caga\v{s}, P.$^{3,4}$}

\IBVSinst{Astronomical Institute ASCR, Fri\v{c}ova 298, CZ-251 65 Ond\v{r}ejov, Czech Republic, \\ \hspace*{0.7cm} e-mail: marek.skarka@asu.cas.cz}
\IBVSinst{Konkoly Observatory, MTA CSFK, Konkoly Thege M. \'{u}t 15-17, 1121 Budapest, Hungary}
\IBVSinst{BSObservatory, Modr\'{a} 587, CZ-760 01 Zl\'{i}n, Czech Republic, e-mail: pavel.cagas@gmail.com}
\IBVSinst{Variable Star and Exoplanet Section of the Czech Astronomical Society, Vset\'{i}nsk\'{a} 941/78,\\ CZ-757 01 Vala\v{s}sk\'{e} Mezi\v{r}\'{i}\v{c}\'{i}, Czech Republic}

\SIMBADobj{V1065 Aql}
\SIMBADobj{FI Sge}
\IBVSobj{CzeV980}
\IBVSobj{CzeV1242}

\IBVStyp{ RRL }
\IBVSkey{photometry}{RR Lyrae}{Blazhko effect}

\IBVSabs{We present a brief report about discovery of modulation in four fundamental-mode RR Lyrae type stars V1065 Aql, CzeV980, FI Sge, and CzeV1242. CzeV980 and CzeV1242 are new RRab type stars that were previously unknown to be variable. The modulation is clearly apparent in all four stars in our data. Our data sets are not appropriate for modulation period determination. However, except for CzeV1242, there are ASAS--SN data available that allow at least rough estimation of the modulation period.}


\begintext

\section{Introduction}
The Blazhko (BL) effect (Blazhko, 1907) is a common feature present in almost half of RR~Lyrae (RRL) stars pulsating in the fundamental mode (Jurcsik et al., 2009; Benk\H{o} et al., 2010). Although it is known for more than a century, not much is known about what stands behind this phenomenon and the explanation of the modulation is still missing (for a review about the Blazhko effect see e.g. Kov\'{a}cs (2016) and Smolec (2016)). About 400 RRLs with the BL effect are catalogued in the Galactic field (Skarka, 2013)\footnote{\tt http://physics.muni.cz/\~{}blasgalf/} and more than 3000 in the Galactic bulge (Prudil \& Skarka, 2017). Due to relatively high incidence rate it is not much difficult to discover modulation in RRL stars that were previously considered to show stable pulsation. This is also the case of V1065 Aql, FI Sge, CzeV980, and CzeV1242, the latter two being a newly discovered RRL type stars.


\section{Observations}\label{Sect:Observation}

All the stars were observed in the scope of survey dedicated to searching for new variable stars (e.g. Caga\v{s} 2017). The strategy is similar as the one of the space telescope {\it Kepler} -- long-term monitoring of one field.

The photometric unfiltered observations were carried out at BSO\footnote{\tt http://www.bsobservatory.org/}, Zl\'{i}n, Czech Republic, using 0.3m Newtonian telescope with coma-corrector (f/4.7) equipped with Moravian instruments CCD G4-16000 (KAF-16803, $4096\times4096$\,px) with field of view (FOV) of 90$\times$90~arcmin. The full FOVs are shown in Fig.~1 and Fig.~2 together with the identification of comparison stars. For the reduction (dark frame and flat field corrections) and aperture photometry we used SIPS software\footnote{\tt http://www.tcmt.org/software.html}. For more details about the data reduction see Caga\v{s} (2017).

The full journal of observations with number of seasons, nights and points is listed in Table 1. Dates of start and end of the observations are given in Table 1 too. Comparison stars used are listed in Table 2. 

\centerline{Table 1. Journal of observations.}
\vskip 2mm
\begin{center}
\begin{tabular}{lccccc}
\hline
Star & Start JD & End JD & Seasons & Nights & Points \\
\hline
V1065 Aql & 2456210 & 2457662 & 4 & 23 & 2534 \\
CzeV980 & 2457241 & 2457662 & 2 & 19 & 2218 \\
FI Sge & 2457989 & 2458046 & 1 & 14 & 1963 \\
CzeV1242 & 2457989 & 2458046 & 1 & 14 & 1955 \\
\hline
\end{tabular}\label{Tab:ObsLog}
\end{center}

\vskip 3mm
\centerline{Table 2. Comparison stars.}
\vskip 2mm
\begin{center}
\begin{tabular}{lcccc}
\hline
Star & Comp ID & RA [\hr~\mm~\sec] & DEC [\deg~\arcm~\arcs] & $V$ [mag] \\
\hline
V1065 Aql & UCAC4 520-117983 & 19 57 27.21 & +13 50 38.3 & 13.129 \\
CzeV980 &   UCAC4 518-117617 & 19 54 16.83 & +13 33 59.1 & 13.160 \\
FI Sge &   UCAC4 538-127230 & 20 13 16.21 & +17 30 37.0 & 13.940  \\
CzeV1242 &  UCAC4 532-123593 & 20 16 06.33 & +16 18 11.5 & 12.590 \\
\hline
\end{tabular}\label{Tab:CompStars}
\end{center}

\section{Analysis}\label{Sect:Analysis}

Because all our data sets have only short extent (one to four seasons) we searched for additional data in large sky surveys. Usable data were found only in the ASAS--SN survey (Kochanek et al., 2017; Shapee et al., 2017). Unfortunately, the data cannot be easily stitched together because of different amplitudes. Thus we analysed the data separately.

For the initial pulsation period estimation we used {\textsc Period04} (Lenz \& Breger, 2005). When the rough period was known, we used LCfit routine (S\'{o}dor, 2012) for more precise period determination and for prewhitening the frequency spectra and searching for peaks close to the main pulsation components (the consequence of the BL effect).

We also estimated times of maximum light using polynomial fitting routine described in Skarka et al. (2015) that we applied to our data. As the zero epoch we used the most-bright well-defined maximum. The light ephemerides and rough estimation of the modulation period are shown in Table 3. Only in V1065~Aql our data give more precise period estimation than ASAS--SN data. BL period was always estimated on the basis of ASAS--SN data, because our data are not appropriate for that purpose.

\IBVSfig{15cm}{6229-f1.eps}{
The full observed FOV with V1065 Aql and CzeV980 with identification of stars.}
\IBVSfigKey{6229-f1.eps}{Full FOV 2}{finding chart}

\IBVSfig{15cm}{6229-f2.eps}{
The full observed FOV with FI Sge and CzeV1242 with identification of stars.}
\IBVSfigKey{6229-f2.eps}{Full FOV 2}{finding chart}


\newpage
\centerline{Table 3. Light ephemerides and Blazhko period estimation. The upper index `a'}
\centerline{in pulsation period means that it is based on the ASAS--SN data.}
\vskip 2mm
\begin{center}
\begin{tabular}{lccc}
\hline
Star & Zero epoch [HJD] & Pulsation period [d] & Blazhko period [d] \\
\hline
V1065 Aql & 2456212.3690(4) & 0.5089976(3) & $\sim$650 \\
CzeV980 &  2457629.4404(2)  & 0.529675(3)$^{a}$ & $\sim$32.8 \\
FI Sge &  2458026.2833(2) & 0.504783(2)$^{a}$ & $\sim$22.4 \\
CzeV1242 &  2458043.2929(4) & 0.415552(7)$^{a}$ & - \\
\hline
\end{tabular}
\end{center}


\section{Remarks on individual stars}\label{Sect:IndividualStars}

\subsection{V1065 Aql}\label{Subsect:V1065Aql}
The variability of V1065 Aql (J2000 19:55:29.89 +14:02:07.5, photographic magnitude 15.5--16.5) was discovered by C. Hoffmeister (1964) on Sonneberg plates. The modulation is well apparent in variation of the amplitude of light changes in both from our and ASAS--SN data (see the two upper panels of Fig.~3). After removing 8 basic pulsation harmonics from the frequency spectra we identified a peak at 1.9632\,c/d (see the detail in the bottom panel of Fig.~3), which suggests the modulation period about 650\,d. From the envelope of the ASAS--SN data shown in the upper panel of Fig.~3 it is apparent that this period could be close to the correct one. However, the identified peak has signal-to-noise ratio (SNR) only about 3.8 and the data contain only one modulation cycle. Thus, the period is only the first, rough estimate.

From the phased light curve in the middle panel of Fig.~3 it is clear that the real modulation amplitude in magnitude is very likely significantly larger than we were able to estimate from our data ($\sim 0.34$\,mag).  

\subsection{CzeV980}\label{Subsect:CzeV980}
CzeV980\footnote{Designation gives the identification in the Czech Variable star catalogue (Br\'{a}t, 2005, Skarka et al., 2017).} (=UCAC4 514-114877, J2000 19:55:04.99 +12:39:29.26, $J=14.463$\,mag, $J-K=0.402$\,mag) lies in the same field as V1065 Aql (see Fig.~1). This star was found to be a new variable of RRab type.

The coverage of our data is very poor since we observed the star only in two consecutive seasons, in the first season having only one night (the original FOV was somewhat shifted in the first two seasons). However, even from these data the modulation is clearly recognizable (see Fig.~4). The star has the full amplitude of the light changes in maximum BL phase about 1\,mag and the amplitude of the modulation is at least 0.23\,mag in clear filter. Similarly as in V1065 Aql, our data are not appropriate for modulation period determination (see the detail in Fig.~4), but data from ASAS--SN survey suggest modulation period of 32.9\,d (the peak to the left from the basic pulsation frequency in the detail of Fig.~4).

\subsection{FI Sge}\label{Sect:FISge}
The variability of FI Sge (J2000  20:13:16.21 +17 30 37.0, V=13.94\,mag) was discovered by Hoffmeister (1936). The star was observed only in 14 nights during the summer season 2017 (see Table 1). Side peak at 2.0303\,c/d (SNR$\sim$4.4) suggests relatively well defined modulation period of the length of 22.4\,d. 

\IBVSfig{15cm}{6229-f3.eps}{
Distribution of V1065 Aql data (top panel), data phased according to ephemerides in Table 3 (middle panel), and corresponding frequency spectra (bottom panel). Different colours in our data (two upper panels) show different seasons, while red asterisks show ASAS--SN data. The light-blue line in the bottom panel shows the frequency spectra based on our data, yellow line shows the residuals after removing 8 pulsation harmonics. The red line shows the residual spectrum based on ASAS--SN data. The detail shows the vicinity of the main pulsation frequency (its position is shown by the black solid line).}
\IBVSfigKey{6229-f3.eps}{V1065 Aql data}{light curve}

\IBVSfig{16cm}{6229-f4.eps}{
The same as in Fig.~3, but for CzeV980.}
\IBVSfigKey{6229-f4.eps}{CzeV980 data}{light curve}

\IBVSfig{16cm}{6229-f5.eps}{
The same as in Fig.~3, but for FI Sge.}
\IBVSfigKey{6229-f5.eps}{FI Sge data}{light curve}

\IBVSfig{16cm}{6229-f6.eps}{
The same as in Fig.~3, but for CzeV1242.}
\IBVSfigKey{6229-f6.eps}{CzeV1242 data}{light curve}

\subsection{CzeV1242}\label{Subsect:CzeV1242}
For CzeV1242 (USNO-A2.0 1050-16748412, J2000 20:11:14.38 +16:43:30.5, $J=15.075$\,mag, $J-K=0.227$\,mag) the ASAS--SN data were of very bad quality. However, there is no doubt about the presence of the BL effect from the middle panel of Fig. 6. Our data were also of insufficient quality for modulation period determination (the detail in the bottom panel of Fig. 6), thus, we are unable to give the rough estimate.


\section{Conclusions}
We report a discovery of the modulation in four RRab stars (V1065 Aql, CzeV980, FI Sge, and CzeV1242). The stars with `CzeV' designation are newly discovered RRab stars. Pulsation periods were estimated from our and ASAS--SN data. We also determined maximum times based on our data. All stars show unambiguous signs of modulation especially in our data (except for V1065 the modulation is not apparent in ASAS--SN data set). In V1065 Aql, CzeV980, and FI Sge we give also first, rough estimates of their modulation periods. More data are needed for a better estimation of the modulation periods and better description of the modulation.

\vskip 5mm

{\bf Acknowledgements:} The financial support of the Hungarian NKFIH Grant K-115709 and Czech Grant GA \v{C}R 17-01752J are acknowledged (MS). 

\references

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\endreferences

\vfill

\section*{Appendix}

\centerline{Table 3. Maximum times with their formal errors.}
\vskip 3mm
\begin{center}
\begin{tabular}{cccccc}
\hline
$T_{\rm max}$	&	Err($T_{\rm max}$ )	&	$T_{\rm max}$	&	Err($T_{\rm max}$ )	&	$T_{\rm max}$	&	Err($T_{\rm max}$ )	\\
\multicolumn{2}{c}{V1065 Aql}			&	2457633.4919	&	0.0005	&	2458026.2833	&	0.0002	\\
2456210.3307	&	0.0015	&	\multicolumn{2}{c}{CzeV980}			&	2458027.2927	&	0.0003	\\
2456212.369	&	0.0004	&	2457609.3308	&	0.0009	&	2458028.3046	&	0.0002	\\
2457546.4698	&	0.0007	&	2457612.5079	&	0.0007	&	\multicolumn{2}{c}{CzeV1242}			\\
2457608.5551	&	0.0004	&	2457627.3204	&	0.0003	&	2457995.519	&	0.0016	\\
2457609.5734	&	0.0006	&	2457628.3809	&	0.0003	&	2457996.3518	&	0.0031	\\
2457624.3337	&	0.0004	&	2457629.4404	&	0.0002	&	2458025.4274	&	0.0008	\\
2457625.3507	&	0.0003	&	2457644.2881	&	0.0011	&	2458026.2594	&	0.0008	\\
2457626.3685	&	0.0003	&	\multicolumn{2}{c}{FI Sge}			&	2458028.3408	&	0.0008	\\
2457627.3866	&	0.0004	&	2457989.4358	&	0.0003	&	2458043.2929	&	0.0004	\\
2457628.4043	&	0.0004	&	2457994.4832	&	0.0005	&	2458043.2929	&	0.0004	\\
2457629.422	&	0.0004	&	2457995.4902	&	0.0004	&	2458045.3628	&	0.0005	\\
2457631.4582	&	0.0003	&	2457996.5007	&	0.0004	&		&		\\
2457632.4755	&	0.0002	&	2458025.2723	&	0.0003	&		&		\\


\hline
\end{tabular}\label{Tab:ObsLog}
\end{center}

\end{document}
