\documentstyle[twoside, epsfig]{article}

\input ibvs2.sty

\begin{document}

\IBVShead{5793}{29 August 2007}

\IBVStitle{Multicolour CCD Photometry of Three RR\lowercase{ab} Stars}

\IBVSauth{S\'odor,~\'A.$^1$; Jurcsik,~J.$^1$; Nagy,~I.$^2$; V\'aradi,~M.$^1$; D\'ek\'any,~I.$^1$; Vida,~K.$^{2,4}$; Hurta,~Zs.$^{2,4}$; Posztob\'anyi,~K.$^2$; Vityi,~N.$^2$; Szing,~A.$^3$; Dobos,~V.$^2$; Kuti,~A.$^2$}

\IBVSinst{Konkoly Observatory of the Hungarian Academy of Sciences, P.O. Box 67, 
          H-1525 Budapest, Hungary; e-mail: sodor@konkoly.hu}
\IBVSinst{E\"otv\"os Lor\'and University, Department of Astronomy, P.O. Box 32,
          H-1518 Budapest, Hungary}
\IBVSinst{University of Szeged, Dept. of Exp. Physics and Astron. Obs., 
          H-6720 Szeged, D\'om t\'er 9, Hungary}
\IBVSinst{Visiting Astronomer, Konkoly Observatory of the Hungarian Academy of Sciences}

\SIMBADobj{BK Cas}
\SIMBADobj{EZ Cep}
\SIMBADobj{ET Per}
\GCVSobj{BK Cas}
\GCVSobj{EZ Cep}
\GCVSobj{ET Per}

\IBVStyp{  RRab  }
\IBVSkey{Variable stars, RR Lyrae stars}
\IBVSabs{Multicolour CCD observations of three RRab stars are presented.}


\begintext

\vspace*{-0.8cm}

We present multicolour CCD photometric observations of the three monoperiodic fundamental mode RR Lyrae variables BK Cas, EZ Cep, and ET Per.
These stars were targets of our survey of brighter, northern, short period fundamental mode RR Lyrae variables (S\'odor, 2007). The observations of all the three stars span two seasons, that is about 200$-$400 days. During these intervals none of them showed light curve variation exceeding our photometric accuracy which was somewhat less than 0.01\,mag. Our light curves consist typically of 350$-$600 data points in each band.

Earlier photometric observations of BK~Cas were published by Goranskij et al. (1973) and Schmidt \& Seth (1996). NSVS (Wozniak et al., 2004) and Hipparcos (ESA, 1997) photometry is available of EZ~Cep. ET~Per was observed by Schmidt \& Reiswig (1993) and by the NSVS (Wozniak et al., 2004). The few number of data points and/or the large errors of these observations do not allow to study the light curve stability of these variables and provide Fourier parameters only with large uncertainty.

Our observations were made with the 60\,cm automatic telescope of Konkoly Observatory, Sv\'abhegy, Budapest, equipped with a Wright 750x1100 CCD camera using $BVI_{\rm C}$ filters. ET Per was also observed with a Photometrics AT 200 CCD camera and $BVR{\rm _C}I_{\rm C}$ filters attached to the 60/90\,cm Schmidt telescope of Konkoly Observatory, Piszk\'estet\H o mountain station. Log of observations are summarized in Table 1.

\begin{table}[!h]
\normalsize
\centerline{{\bf Table~1.} Log of observations}
\begin{center}
\begin{tabular}{llclcll}
Star & Comparison & $V_{\rm comp}$\,$^*$ & Observation period & No. of nights & filters & telescope \\
     &            &   [mag]              &                    &               &         &           \\
%\multicolumn{2}{c}{$P_\mu$} & Type \\
\hline
BK Cas & GSC 4025-01395 & 12.74 & 2453991 -- 2454328 & 11 & $VI_{\rm C}$ & 60\,cm \\
EZ Cep & GSC 4521-00784 & 13.63 & 2453964 -- 2454166 & 26 & $BVI_{\rm C}$ & 60\,cm \\
ET Per & GSC 3671-01241 & 11.90 & 2453728 -- 2453751 &  4 & $BVR_{\rm C}I_{\rm C}$ & Schmidt \\
ET Per & GSC 3671-01241 & 11.90 & 2453988 -- 2454171 &  8 & $BVI_{\rm C}$ & 60\,cm \\
\hline
\multicolumn{7}{l}{\footnotesize{$^*$ $V$ magnitudes of the comparison stars from the NOMAD catalogue (Zacharias et al., 2004).}}\\
\end{tabular}
\end{center}
\vspace*{-0.6cm}
\end{table}

\vskip 4mm

CCD reduction and photometry was performed using standard IRAF\IBVSfm packages. Instrumental magnitudes were transformed to the standard $BVR_{\rm C}I_{\rm C}$ system by observing photometric standards in M67 (Chevalier \& Ilovaisky, 1991) with both telescopes.

\IBVSfoot{{\sc IRAF} is distributed by the National Optical Astronomy Observatories, which are operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation.} 

\newpage

\IBVSfig{10.5cm}{5793-f1.eps}{Differential $V$ and $V-I_{\rm C}$ light and colour curves of BK Cas.}
\IBVSfigKey{5793-f1.eps}{BK Cas}{light curve}

\IBVSfig{10.5cm}{5793-f2.eps}{Differential $V$, $B-V$ and $V-I_{\rm C}$ light and colour curves of EZ Cep.}
\IBVSfigKey{5793-f2.eps}{EZ Cep}{light curve}

\IBVSfig{10.5cm}{5793-f3.eps}{ Differential $V$, $B-V$, $V-R_{\rm C}$ and $V-I_{\rm C}$ light and colour curves of ET Per.}
\IBVSfigKey{5793-f3.eps}{ET Per}{light curve}

Our photometric data available electronically from the IBVS website (5793-t5.txt$-$5793-t16.txt) list the relative $BVR_{\rm C}I_{\rm C}$ magnitude and relative $B-V, V-R_{\rm C}$ and $V-I_{\rm C}$ colour time series with respect to the comparison stars. The constancy of the brightness of the comparisons was checked by measuring magnitude differences to several check stars in our field of view. The $r.m.s.$ scatter of these data is between 0.006 and 0.01\,mag in each band in accordance with the $r.m.s.$ scatter of the Fourier fit of the light curves of the variables. The $V$ light curves and the colour curves of the three stars are plotted in Figs.~$1-3$.

\IBVSedata{5793-t5.txt}
\IBVSdataKey{5793-t5.txt}{BK Cas}{photometry}
\IBVSedata{5793-t6.txt}
\IBVSdataKey{5793-t6.txt}{BK Cas}{photometry}
\IBVSedata{5793-t7.txt}
\IBVSdataKey{5793-t7.txt}{BK Cas}{photometry}
\IBVSedata{5793-t8.txt}
\IBVSdataKey{5793-t8.txt}{EZ Cep}{photometry}
\IBVSedata{5793-t9.txt}
\IBVSdataKey{5793-t9.txt}{EZ Cep}{photometry}
\IBVSedata{5793-t10.txt}
\IBVSdataKey{5793-t10.txt}{EZ Cep}{photometry}
\IBVSedata{5793-t11.txt}
\IBVSdataKey{5793-t11.txt}{EZ Cep}{photometry}
\IBVSedata{5793-t12.txt}
\IBVSdataKey{5793-t12.txt}{ET Per}{photometry}
\IBVSedata{5793-t13.txt}
\IBVSdataKey{5793-t13.txt}{ET Per}{photometry}
\IBVSedata{5793-t14.txt}
\IBVSdataKey{5793-t14.txt}{ET Per}{photometry}
\IBVSedata{5793-t15.txt}
\IBVSdataKey{5793-t15.txt}{ET Per}{photometry}
\IBVSedata{5793-t16.txt}
\IBVSdataKey{5793-t16.txt}{ET Per}{photometry}


Fourier parameters of the $V$ light curves are listed in Table~2. Normal and discrete maximum timings are given in Table~3.

\begin{table}[b!]
\normalsize
\centerline{{\bf Table~2.} Fourier parameters of the $V$ light curves.}
\begin{center}
\begin{tabular}{c@{\hspace{8pt}}c@{\hspace{8pt}}c@{\hspace{8pt}}c@{\hspace{8pt}}c@{\hspace{8pt}}c@{\hspace{8pt}}c@{\hspace{8pt}}c@{\hspace{8pt}}c@{\hspace{8pt}}c@{\hspace{8pt}}c}
Star &  $P$ & $A_1$    & $R_{21}$ & $R_{31}$ & $R_{41}$ & $R_{51}$ & $\phi_{21}$\,$^*$ & $\phi_{31}$\,$^*$ & $\phi_{41}$\,$^*$ & $\phi_{51}$\,$^*$ \\
     & [d]& [mag] &     &     &     &     & [rad]       & [rad]       & [rad]       & [rad]       \\
\hline
BK Cas & 0.3902700(2) & 0.306 & 0.539 & 0.301 & 0.167 & 0.095 & 2.612 & 5.461 & 1.978 & 4.647 \\
EZ Cep & 0.3790035(1) & 0.393 & 0.572 & 0.349 & 0.231 & 0.137 & 2.431 & 5.266 & 1.675 & 4.421 \\
ET Per & 0.3940135(1) & 0.439 & 0.542 & 0.369 & 0.239 & 0.166 & 2.320 & 5.042 & 1.346 & 4.098 \\
\hline
\multicolumn{11}{l}{\footnotesize{$^*$ Phase differences are given according to sine term decomposition.}} \\
\end{tabular}
\end{center}
\end{table}
\vskip 2mm

Spectroscopic [Fe/H] values from the literature (transformed to the metallicity scale used by Jurcsik \& Kov\'acs, 1996) and [Fe/H] calculated from the Fourier parameters according to the formula derived in Jurcsik \& Kov\'acs (1996) are given in Table~4. The metallicity of EZ~Cep given by Mendes de Oliveira \& Smith (1990) seems to be erroneous, as it differs significantly from the other two [Fe/H] determinations.


\begin{table}[!ht]
\centerline{{\bf Table~3.} Normal and discrete maximum timings of the $V$ light curves.}
\begin{center}
\begin{tabular}{cll}
Star & $T_{\rm max}$ - 2450000 & type \\
     & [HJD] & \\
\hline
BK Cas & 54019.4667 & Normal \\
       & 54327.1793 & Normal \\
EZ Cep & 54005.4023 & Normal \\
       & 54166.478  & Discrete \\
ET Per & 53733.9048 & Normal \\
       & 54000.2585 & Normal \\
       & 54171.262  & Discrete \\
\hline
\end{tabular}
\end{center}
\vspace*{0.2cm}
\centerline{{\bf Table~4.} Spectroscopic and photometric [Fe/H] values.}
\begin{center}
\begin{tabular}{c@{\hspace{26pt}}r@{\hspace{26pt}}c}
Star&[Fe/H]$_{\rm phot}$ & [Fe/H]$_{\rm spect}$ \\
\hline
BK Cas &  $+0.21$ &               \\
EZ Cep &  $ 0.00$ & $-0.01$\,$^a$ \\
       &          & $-0.92$\,$^b$ \\
ET Per &  $-0.38$ &               \\
\hline
\multicolumn{3}{l}{$a$: Fernley \& Barnes (1997)} \\
\multicolumn{3}{l}{$b$: Mendes de Oliveira \& Smith (1990)}
\end{tabular}
\end{center}
\end{table}

We thank B\'ela Szeidl for his many helpful comments on this work. The financial support of OTKA grants T-048961, and T-068626 is acknowledged.

\references

Chevalier, C. \& Ilovaisky, S.A., 1991, {\it A\&A Suppl. Ser.}, {\bf 90}, 225

ESA, 1997, {\it The Hipparcos Catalogue}, ESA SP-1200

Fernley, J. \& Barnes, T.G., 1997, {\it A\&AS}, {\bf 125}, 313

Goranskij, V.P., Kazarovets, E.V. \& Shugarov, S.Y., 1973, {\it PZP}, {\bf 1}, 477

Jurcsik, J., \& Kov\'acs, G., 1996, {\it A\&A}, {\bf 312}, 111 

Mendes~de~Oliveira, C. \& Smith, H.A., 1990, {\it PASP}, {\bf 102}, 652

Schmidt, E.G. \& Reiswig, D.E., 1993, {\it AJ}, {\bf 106}, 2429

Schmidt, E.G. \& Seth, A., 1996, {\it AJ}, {\bf 112}, 2769

S\'odor, \'A, 2007, {\it AN}, in press, arXiv/0704.3341

Wozniak, P. R. et al., 2004, {\it AJ}, {\bf 127}, 2436

Zacharias, N., Monet, D.G., Levine et al., 2004, {\it AAS}, {\bf 205}, 4815

\endreferences

%From: IBVS 5859
\vskip20pt
\IBVSerratum{5793}
\vskip6pt
In IBVS 5793 Table 3 the 2nd line on the maximum timings of BK Cas gives erroneous $T_{\mathrm max}$ value. This line should correctly be: ``BK Cas {\bf 54321.1434} normal''.
% ``BK Cas \hskip5mm 54321.1434 \hskip5mm normal''


\end{document}
