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\IBVShead{6068}{14 August 2013}

\IBVStitletl{C\lowercase{ze}V283 and C\lowercase{ze}V397 -- new RR Lyrae stars showing}{ Blazhko effect}


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

\IBVSinst{Department of Theoretical Physics and Astrophysics, Faculty of Science, Masaryk University, Kotl\'a\v rsk\'a 2, Brno, Czech Republic, e-mail: maska@physics.muni.cz}

\IBVSinst{BSObservatory, Modr\'a 587, 760 01, Zl\'in, Czech Republic, e-mail: pavel.cagas@gmail.com}



\SIMBADobj{USNO-A2.0 0975-17144916}
\SIMBADobj{USNO-A2.0 0975-11853460}
\IBVStyp{ RRab }
\IBVSkey{photometry}

\begintext

	We present discovery of the Blazhko effect in two fundamental mode RR Lyrae variables CzeV283$=$USNO-A2.0 0975-17144916 
	(J2000 $\alpha=19^{\mathrm{h}}55^{\mathrm{m}}38^{\mathrm{s}}$\hspace{-0.3em}.1, $\delta=+13^{\circ}43'22.4''$, Aql) 
	and CzeV397$=$USNO-A2.0 0975-11853460
	(J2000 $\alpha=18^{\mathrm{h}}29^{\mathrm{m}}43^{\mathrm{s}}$\hspace{-0.3em}.3, $\delta=+12^{\circ}06'39''$\hspace{-0.3em}.2'', Her), 
	whose variabilities were unveiled recently (in 2011 and 2012) in the framework of private project dealing with searching for new 
	variables in randomly chosen fields around known variables. This observation program resulted in discovery of more than a hundred new 
	variable stars (see http://www.bsobservatory.org/results.html) among which some interesting cases occurred -- e.g. a quadruple eclipsing 
	binary system CzeV343 in Auriga constellation (Caga\v{s} \& Pejcha 2012).
	
	The Blazhko effect, known for about century (firstly noted by S.\,N.\,Blazhko 1907), 
	manifests itself as amplitude and phase modulations of the light curve. This phenomenon represents actual astrophysical 
	challenge, because its nature remains unexplained. The most recent explanation, which is based on the data from {\it Kepler} space 
	telescope, deals with the resonance 9:2 between the fundamental mode and the 9th radial overtone (Szab\'{o} et al. 2010). A brief 
	overview of the Blazhko effect and proposed models can be found e.g. in Kolenberg (2011). 
	
	CzeV283 and CzeV397 join a group of about 270 known Blazhko stars from the Galactic field.\footnote{A list with Blazko variables 
	is available at {\tt http://physics.muni.cz/\~{}blasgalf/} (Skarka 2013)} Except for results based on space missions, the most 
	significant progresses in Blazhko variables research are {\it The Konkoly Blazhko survey} (Jurcsik et al. 2009) and 
	works based on {\it GEOS} database (Le Borgne et al. 2007).
	
	The surroundings of V729 Aql and V1134 Her were observed during three seasons between 2011 and 2013 (see Table 1 with a journal of 
	observation) with a 10 inch f/5.4 Newtonian telescope equipped with a G4-16000 CCD camera\footnote{ Parameters of the detector can be 
	found at {\tt http://www.gxccd.com/}} (field of view $71'\times71'$) at the private observatory in Zl\'{i}n, Czech Republic. As the aim of these 
	measurements was searching for new variables, observations were carried out without filtering to gain the highest possible throughput. 
	
	Raw images, with exposure times of 240 and 180~seconds, were calibrated with appropriate dark frames and flat fields. Differential 
	aperture photometry as well as the calibrations were performed using \textsc{C-Munipack}\footnote{{\tt http://c-munipack.sourceforge.net/}} 
	software. USNO-A2.0~0975-17184388 (in CzeV283) and USNO-A2.0~0975-11774493 (in CzeV397) were chosen as comparison stars. In total we 
	gained 910 measurements for CzeV283 in 19 nights with a time span of 413~d and 1255 points for CzeV397 in 22 nights (time span of 678~d). 
	The relative precision of our photometry was about 0.05~mag.
	
	We performed a frequency analysis of our time series with \textsc{Period04} (Lenz \& Breger 2005) to get the basic 
	pulsation periods. As we caught several maxima of both stars (Table~2), we were also able to determine their timings using 
	polynomial fitting. On the basis of our investigations we give	
	\begin{equation}
   	\mathrm{HJD}~T_{\mathrm{max}}=2456222.3286(6)+0.558488(2)E_{\mathrm{puls}},
	\end{equation}  	
	for CzeV283 and 
	\begin{equation}
   	\mathrm{HJD}~T_{\mathrm{max}}=2456132.3955(4)+0.58664(3)E_{\mathrm{puls}},
	\end{equation}	
	for CzeV397, respectively. Data of studied stars phased with respect to these elements are plotted in Fig. 1.
	
\vskip 8mm
\centerline{Table 1. Journal of observations. The meaning of $t$ is the duration of observation, }
\centerline{$N$ is the number of points and TS corresponds to the time span.}
\begin{center}
\begin{tabular}{cccccc}
\hline

	\multicolumn{3}{c}{CzeV283} & \multicolumn{3}{c}{CzeV397} \\
	Night & $t$ & $N$ & Night & $t$ & $N$ \\
	$[$ HJD-2450000$]$ & $[$hours$]$& & $[$HJD-2450000$]$ & $[$hours$]$ &  \\
	5834&3.7&39&5830&1.6&27 \\
	5836&3.1&38&5835&3.1&43\\
	5851&4.1&34&6095&3.0&26\\
	5856&4.1&36&6101&1.1&19\\
	5857&3.4&39&6102&2.7&47\\
	5867&1.7&17&6121&3.6&64\\
	5868&4.0&45&6131&4.3&69\\
	5869&3.9&44&6132&3.8&66\\
	5875&4.2&44&6145&1.5&22\\
	5876&3.2&35&6152&3.6&64\\
	6204&5.0&88&6153&2.4&41\\
	6210&2.5&42&6155&4.2&68\\
	6212&4.9&87&6157&3.1&56\\
	6220&3.8&64&6158&4.5&75\\
	6221&3.0&52&6159&4.3&75\\
	6222&3.2&56&6180&4.7&79\\
	6223&3.7&65&6181&2.8&40\\
	6246&2.4&43&6483&4.2&66\\
	6247&2.4&42&6494&5.1&89\\
					 &&&6495&4.8&85\\
					 &&&6507&4.1&72\\
					 &&&6508&4.0&62\\
	\multicolumn{6}{c}{Total} \\
	TS=413~d&66.3&910&TS=665~d&68.4&1121\\
\hline
\end{tabular}
\end{center}
	
	After a few nights it was obvious that the light curves of both stars underwent changes (see Fig.~2), 
	which is the sign of the Blazhko effect. Unfortunately our data were too sparse to estimating the Blazhko period. In the 
	case of CzeV397 we identified a suspicious side peak near $f_{0}$, which corresponds to 38~day modulation period. This period 
	gives nice phased light curve, but it needs to be confirmed by further observations.


\vskip 8mm


\centerline{Table 2. Times of maximum light.}
\begin{center}
\begin{tabular}{cc}
\hline

	CzeV283 & CzeV397 \\

	2455836.4148(8)&2456102.4842(4)\\
	2455868.2524(9)&2456132.3955(4)\\
	2456212.2797(5)&2456159.3754(3)\\
	2456222.3286(6)&2456495.5320(14)~ \\
	&							 2456508.4267(4) \\
\hline
\end{tabular}
\end{center}
	
	To have at least a rough idea about the amplitude of the light changes of the stars we used \textsc{Period04} and 
	fitted data with the sum of sines (the mean light curves in Fig. 1) in the form 
	
	\begin{equation}
   	A(t)=A_{0}+\sum^{n}_{i=1} A_{i} \sin  \left[ 2\pi \left(  i \tau  + \phi_{i} \right) \right],
	\end{equation}
	where $\tau$ corresponds to the phase of the light curve (fractional part of $\left( \frac{t-T_{0}}{P}\right)$, 
	where $T_{0}$ is the epoch and $P$ is the basic pulsation period). The degree of the fit ($n$) was chosen according to visual inspection.
	
	For CzeV283 we obtained min-to-max\footnote{We simply substracted minimum value of the fit from maximum.} range 
	$\Delta \mathrm{mag}=0.93$ and $\Delta \mathrm{mag}=0.67$ for CzeV397, respectively.  

\IBVSfig{8cm}{6068-f1.eps}{Data of CzeV283 and CzeV397 phased according to eq. 1 and 2, respectively. Solid line represents the fit 
with the sum of sines with respect to (3) of the degree $n$.} 		
\IBVSfigKey{6068-f1.eps}{CzeV283, CzeV397}{light curve}

\IBVSfig{8cm}{6068-f2.eps}{Close-up of the vicinities of the maxima of phased 
light curves. Change of the shape and amplitude in different nights is easily noticeable.} 
\IBVSfigKey{6068-f2.eps}{CzeV283, CzeV397}{light curve}

M. Skarka acknowledges the financial support of MU~MUNI/A/0735/2012. 
	
\vfill\eject

\references
	
Caga\v{s}, P., \& Pejcha, O.\ 2012, {\it A\&A}, {\bf 544}, L3 %\BIBCODE{2012A&A...544L...3C}

Jurcsik, J., S{\'o}dor, {\'A}., Szeidl, B., et al.\ 2009, {\it MNRAS}, {\bf 400}, 1006 %\BIBCODE{2009MNRAS.400.1006J}

Kolenberg, K.\ 2011, RR Lyrae Stars, Metal-Poor Stars, and the Galaxy, Carnegie Obs. Astrophys. Ser., vol. 5, ed. A. McWilliams, p.\,100 \BIBCODE{2012JAVSO..40..289H}

Lenz P., Breger M., 2005, {\it Comm. Asteroseismology}, {\bf 146}, 53	

Le Borgne, J.~F., Paschke, A., Vandenbroere, J., et al.\ 2007, {\it A\&A}, {\bf 476}, 307 %\BIBCODE{2007A&A...476..307L}

Skarka, M.\ 2013, {\it A\&A}, {\bf 549}, A101 %\BIBCODE{2013A&A...549A.101S}

Szab{\'o}, R., Koll{\'a}th, Z., Moln{\'a}r, L., et al.\ 2010, {\it MNRAS}, {\bf 409}, 1244 %\BIBCODE{2010MNRAS.409.1244S}

\endreferences


\IBVSedata{6068-t3.txt}
\IBVSdataKey{6068-t3.txt}{CzeV283}{photometry}
\IBVSedata{6068-t4.txt}
\IBVSdataKey{6068-t4.txt}{CzeV397}{photometry}


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