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\IBVShead{6051}{26 March 2013}

\IBVStitletl{First result of the Czech RR Lyrae Stars Observation Project}{ - a new Blazhko star CN~C\lowercase{am}}

\IBVSauth{Skarka, M.$^1$; Ho\v{n}kov\'{a}, K.$^2$; Jury\v{s}ek, J.$^2$}

\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{Observatory and Planetarium of Johann Palisa, V\v{S}B � Technical University of Ostrava, 17. listopadu 15, Ostrava-Poruba, Czech Republic}

\SIMBADobj{CN Cam}
\IBVStyp{ RRab }
\IBVSkey{photometry}

\begintext

	We introduce a new project which attempts to provide precise, filtered measurements of RR Lyraes, which were not 
	observed by automatic surveys (or the survey data were of bad quality), and which were not studied in detail, or are somehow interesting. 
	The basic goal is to obtain well-covered light curves to determine ephemerides, periods, light curve characteristics 
	(amplitude, rising time) and finally to obtain Fourier parameters to estimate the basic physical parameters.
	
	We founded a project now called {\it The Czech RR Lyrae Stars Observation Project} (hereafter CRRLSOP), which cooperates with amateur 
	observers from the Variable Star and Exoplanet Section of Czech Astronomical Society.\footnote{http://var2.astro.cz/EN/} In 2012 our group 
	comprised five members and we hope that this number will increase in years to come. A similar, but professional survey, dealing with RR Lyraes 
	is under way in Hungary -- {\it The Konkoly Blazhko Survey} (S\'odor 2007). They use only one telescope contrary to our 
	project that using many telescopes. Another project focused on RR Lyraes cooperating with amateurs is {\it GEOS RR Lyr database} (Boninsegna et al. 2002). 
	The GEOS database deals with maxima timings of RR Lyraes.

	To be able to get data of high quality, CRRLSOP focuses on bright RR Lyraes with V$<12$~mag at maximum light. 
	This value is chosen to suit the telescopes that amateurs use, which are typically of the diameter between 20 and 30 cm. 
	Another restriction is imposed by the location of the Czech Republic. We choose targets with a declination of typically 
	more than 20$^{\circ}$, which are easily observable for a long time during the year.  
	
	Each target is carefully selected to suit an observer's equipment and taking the observer's time constrains into account. 
	Observers are briefed in detail about exposure times and about field of view selection. All the observations 
	are subsequently discussed. Each star is monitored by only one observer to avoid merging data from different devices. We 
	also put emphasis on the comparison star selection.
		
	All the measurements gathered by observers are processed in the same way using aperture photometry software 
	\textsc{CMunipack}.\footnote{http://c-munipack.sourceforge.net/} 
	The structure of the observations is as follows: stars which are expected to have a 
	stable light curve are observed two nights in a row followed by observations taken after one week, a few weeks and finally after 
	a few months to verify the stability of the stellar pulsation. In the case of Blazhko stars, the objects are monitored as 
	often as possible to cover all Blazhko phases. The time schedule of observations is not strictly given, because of 
	weather or other unpredictable reasons.\\

	CN Cam (= NSV 5256 = SAO1900 = BD+82 338 = GSC 04556-00251, J2000 \linebreak  11\hr 36\mm 11\fsec8, +81\deg 17\arcm 37\farcs1), found to be a variable by Strohmeier \& Knigge (1961), 
	was first proposed to be an eclipsing binary. Based on a 12-night study, Campos-Cucarella et al. (1996) (hereafter CC96) classified CN Cam as 
	an RRab star and established its period as 0.6214(1)~d. Kinman et al. (2007) (hereafter K07) improved the period to 0.621445(2)~d and determined 
	the amplitude of the light changes to be 0.36 mag in $V$ and 0.49 mag in $B$, CC96 gives 0.350(5)~mag 
	in $V$ and 0.474(4) mag in $B$. K07 also estimated the metallicity of CN Cam using Fourier coefficients, amplitude in $V$ and rise-time 
	(methods listed in Sandage (2004)). The values of metallicity that K07 obtained were around $[\mathrm{Fe}/\mathrm{H}]=-1.1$. 
	K07 found the distance of CN Cam as 594 pc.
			
	One of the most recent observations was performed by Maintz (2012). Between the years 2006 and 2012 she obtained 
	seven maxima timings and improved the value of the period to 0.6214465(3)~d. The Blazhko effect was not noted in any of these works. \\
		
	We observed CN Cam in $BVR_{c}I_{c}$ passbands during 20 nights from the end of January till the  end of June 2012.
	We obtained between 1340 and 1630 points in each filter. Observations were carried out using the 20-cm Newtonian telescope 
	of the Observatory and Planetarium of Johann Palisa in Ostrava equipped with an SBIG-ST8 XME camera. The data were 
	reduced in the classic way and were transformed into the standard Johnson-Cousins magnitudes using stars in Landolt fields 
	(Landolt 1992). 
		
	Similarly as CC96 and K07, we used GSC~04556-00278 (= SAO1899 = BD+82 337) as a comparison star 
	and GSC 04556-00278 as a check star. According to the $J=9.453(23)$ and $K=9.248(22)$ magnitudes of the comparison taken from 2MASS 
	All-Sky Catalog of Point Sources (Cutri et al. 2003) we got Johnson-Cousins magnitudes of the comparison via 
	the relations in Warner (2007) (see Table 1). Our $V=10.24(5)$ magnitude of the comparison fall between the magnitudes given by CC96 and K07 
	(10.3 and 10.201(3) mag, respectively). 
	
\vskip 5mm
\centerline{Table 1. Observation log and magnitude of the comparison star in different passbands.}
\vskip 3mm
\begin{center}
\begin{tabular}{cccccc}
\hline
	 Nights & Time-span [d] & $B$ & $V$ & $R_{c}$ & $I_{c}$ \\ \hline
	 20 & 186 & 1341 & 1498 & 1495 & 1629 \\\hline
	 \multicolumn{2}{c}{brightness of the comparison star [mag]} & 10.62(9) & 10.24(5) & 10.01(5) & 9.77(5) \\
\hline
\end{tabular}
\end{center}		
 
	After performing the period analysis with \textsc{Period04} (Lenz \& Breger 2005) we found the following ephemeris:	
	\begin{equation}
   	\mathrm{HJD}~T_{\mathrm{max}}=2455959.4707(36)+0.621446(3)E_{\mathrm{puls}}.
	\end{equation}	
	The time of the extremum is based on the $V$ data and it was determined using \textsc{\small LESVEPHOTOMETRY} software (de Ponthi�re 2010) 
	by fitting the light curve with a smoothing spline function (Reinsch 1967). The value of the period is within the error bars 
	in agreement with the period determined by Maintz (2012).
		
	Frequency analysis with \textsc{Period04} revealed additional frequency peaks on the right-hand side of the basic 
	pulsation frequency ($f_{0}=1.6091504(73)$ c/d) and its harmonics ($kf_{0}$, where $k=1,2,3...$). Such a frequency 
	structure is one of the most noticeable manifestations of the Blazhko effect. In total we identified peaks related to the basic 
	pulsation frequency up to $k=8$ and four peaks corresponding to the modulation frequency ($kf_{0}+f_{B}$ up to $k=4$). The spacings of the side peaks were
	not equidistant, but they were slightly decreasing with rising $k$. The side peak with the highest amplitude was $f_{0}+f_{B}=1.629877(61)$~c/d. 
	Therefore we give the first rough estimation of the Blazhko period of CN Cam $P_{\mathrm{BL}}=48.25(14)$~d.\footnote{All values of frequencies and 
	periods in this paragraph are based on $V$ data analysis}	
		
\IBVSfig{11.5cm}{6051-f1.eps}{Calibrated data of CN Cam folded according to equation 1. The solid lines are the light curve fit with the sum of sines.} 
\IBVSfigKey{6051-f1.eps}{CN Cam}{light curve}
				
	Although the coverage of the light curves was not ideal, we fitted $V$, $B-V$, $V-R$ and $V-I$ data with the 
	sum of sines and we got the approximations of the mean light curves (Figure 1). The degree of the fit was chosen based on visual inspection. 
	Analysing the mean light curves allowed us to determine Fourier coefficients based on the sine-term decomposition of the $V$ light curve, and it 
	also allowed us to estimate mean color indices, mean magnitudes (zero points), mean amplitudes and mean rise-time (duration from minimum to maximum in phase) 
	during the Blazhko cycle (see Table 2). The times and the values of the extrema for rise-time and amplitude estimation 
	were determined using \textsc{\small LESVEPHOTOMETRY} as mentioned above.   
 	  	
	We could estimate metallicity of CN Cam using Fourier coefficients and pulsation period. Formula (3) from 
	Jurcsik \& Kov\'{a}cs (1996) gives $\mathrm{[Fe/H]}_{\mathrm{JK}}=-0.90$ dex. Transforming this value to the more common Zinn \& West (1984) 
	scale using the $\mathrm{[Fe/H]}_{\mathrm{ZW}} = 1.05\mathrm{[Fe/H]}_{\mathrm{JK}}-0.20$ relation, adopted from Sandage (2004), 
	we obtained $\mathrm{[Fe/H]}_{\mathrm{ZW}}=-1.15$ dex, which agrees well with the spectroscopic value $\mathrm{[Fe/H]}=-1.2$ dex given in K07. 

	Following the analysis in K07, our parameters gave: $\mathrm{[Fe/H]}=-1.15$ with Sandage's equation (3),\footnote{to use Sandage's (2004) equation (3), 
	$\phi_{31}$ from the Table 2 has to be decreased by the parameter $\pi$} $\mathrm{[Fe/H]}=-1.05$ with Sandage's relation (6) and $\mathrm{[Fe/H]}=-1.00$ 
	with Sandage's equation (7) (with rise-time 0.272). If we fix our metallicity at $\mathrm{[Fe/H]}=-1.15$~dex and consider the calibration	
	\begin{equation}
   	M_{V}=0.214\mathrm{[Fe/H]}+0.86
	\end{equation}	
	of Clementini et al. (2003) we obtain $M_{V}=0.61$~mag. The distance of CN Cam is therefore 608~pc.\footnote{taking into 
	account the extinction E$(B-V)=0.047$ from Schlegel et al. (1998)}

\vskip 5mm
\centerline{Table 2. Characteristics of the light curves and sine-term Fourier coefficients based on}
\centerline{the $V$ light curve fit. $N$ is the degree of the fit, $A_{0}$ denotes the mean magnitude. Phases}
\centerline{$\phi_{ij}$ are in radians, Fourier combinations $R_{ij}$ in mag.}
%\vskip 3mm
\begin{center}
\begin{tabular}{cccccc}
\hline
	        & $N$  & $A_{0}$ [mag]& max [mag] &amplitude [mag]    & rise-time  \\ \hline
	 $B$    & 4  & 10.1168(7)   & 9.817(3)  &0.510(4)           & 0.268(4) \\                       
	 $V$    & 4  & 9.6751(4)    & 9.460(2)  &0.384(3)           & 0.272(4) \\
	 $R_{c}$& 4  & 9.3703(4)    & 9.207(2)  &0.313(3)           & 0.272(4) \\
	 $I_{c}$& 4  & 9.0460(3)    & 8.925(2)  &0.253(3)           & 0.282(4) \\
	 $B-V$  & 4  & 0.4456(4)    & 0.358(2)  &0.130(4)           &\\
	 $V-R$  & 5  & 0.3022(3)    & 0.252(4)  &0.079(4)           &\\
	 $V-I$  & 5  & 0.6262(9)    & 0.531(3)  &0.149(4)           &\\ \hline
	 $\phi_{21}$ & $\phi_{31}$ & $\phi_{41}$ & $R_{21}$ & $R_{31}$ & $R_{41}$ \\ \hline
	 2.578(13) & 5.567(28) & 2.984(74) & 0.365(5) & 0.155(4) & 0.054(4) \\
\hline
\end{tabular}
\end{center}
	
 	Amplitudes and zero points of our mean light curves differ from the values given by CC96 and K07. Our range in $(B-V)$ 
 	(0.358(2)-0.488(3)) is significantly higher than $0.26-0.38$~mag (CC96) and $0.325-0.454$~mag (K07). According to our $(B-V)$ range CN Cam varies between 
 	spectral types F2 to F6. Our amplitude in $B=0.510(4)$~mag is also larger than 0.474(4)~mag (CC96) and 0.49~mag (K07).
 	Our metallicity estimation is slightly lower than K07 derived, but close to the value based on spectroscopy. 
 	
 	All the discrepancies are probably caused by changing characteristics during the Blazh\-ko cycle, which 
 	were not caught in CC96 and K07 (visual estimates of the amplitude of the modulation in $V$ is about 0.09 mag and about 0.11 in $B$). 
 	The slightly different magnitude of the comparison star that we used can also play a minor role. Our mean light curves could also differ 
 	from the `true' mean light curves due to non-uniform coverage of our light curves ('true' mean amplitudes of $BVR_{c}I_{c}$ are probably slightly 
 	lower than ours). For more reliable analysis more extended observations will be needed.
 	
\IBVSfig{9cm}{6051-f2.eps}{Standard $V$ data phased with the period 47.25~d according to the epoch given in equation~1.}	
\IBVSfigKey{6051-f2.eps}{CN Cam}{light curve}

	In the future we plan to focus on the observations of other interesting or poorly observed stars with stable and also 
	with modulated light curves. We will also try to complete missing parts of the light curves of already observed stars. 
	Any new observer interested in RR Lyraes is warmly welcome to join CRRLSOP.

\vskip 0.2cm

The financial support of MU~MUNI/A/0735/2012 is acknowledged. 
The International Variable Star Index (VSX) database, operated at AAVSO, 
Cambridge, Massachusetts, USA has been used. This research also has also
used the VizieR catalogue access tool, CDS, Strasbourg, France. We would like to 
thank S. N. de Villiers and our referee for useful comments and suggestions. We would also like to 
thank the director of Observatory and Planetarium of Johann Palisa in Ostrava, Tom\'{a}\v{s} Gr\'{a}f. 

\vskip 4cm

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\endreferences


\IBVSedata{6051-t3.txt}
\IBVSdataKey{6051-t3.txt}{CN Cam}{photometry}
\IBVSedata{6051-t4.txt}
\IBVSdataKey{6051-t4.txt}{CN Cam}{photometry}
\IBVSedata{6051-t5.txt}
\IBVSdataKey{6051-t5.txt}{CN Cam}{photometry}
\IBVSedata{6051-t6.txt}
\IBVSdataKey{6051-t6.txt}{CN Cam}{photometry}

\IBVSCorrectedVersion{Apr  3 13:40:03 CEST 2013}
\end{document}
