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\input ibvs2.sty

\begin{document}

\IBVShead{5709}{26 June 2006}

\IBVStitle{$\mathrm{BVR_cI_c}$ photometry of three RRab stars}

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

\IBVSinst{Konkoly Observatory of the Hungarian Academy of Sciences, P.O.
Box 67, H-1525 Budapest, Hungary; e-mail: jurcsik@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{Astrophysikalisches Institut Potsdam, An der Sternwarte 16,
14482 Potsdam, Germany}

\SIMBADobj{BH Aur}
\SIMBADobj{TZ Aur}
\SIMBADobj{TW Lyn}
\GCVSobj{BH Aur}
\GCVSobj{TZ Aur}
\GCVSobj{TW Lyn}

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

\begintext

The discovery of small amplitude light curve modulation of RR Gem and SS
Cnc (Jurcsik et al., 2005, 2006) warns that having not enough extended and
accurate photometry similar modulation behaviour of RR Lyrae stars may
have escaped detection. In this note CCD observations of three RRab stars
(TZ Aur, BH Aur, TW Lyn) extending over 20-30 days intervals are
published.

Photoelectric observations of TZ Aur were obtained by Fitch et al.\
(1966), Sturch (1966), Stepien (1972), and Epstein (1969). Because of the
inhomogeneity, their observations did not allow to resolve smaller light
curve changes. For TW Lyn and BH Aur only a few, $V$ and $R$ band
measurements were published by Schmidt et al.\ (1995) and Schmidt \&
Reiswig (1993), respectively. According to our observations the light
curves of the three stars remain stable within the accuracy limit of the
photometry. Our data do not, however, exclude the possibility of light
curve changes on longer time scales.

The observations were made with the 60-cm automatic telescope of Konkoly
Observatory, Sv\'abhegy, Budapest, equipped with a Wright $750 \times
1100$ CCD camera using $BVR_CI_C$ filters. Log of observations are
summarized in Table 1.

\begin{table}[!h]
\normalsize
\centerline{Table 1. Log of observations}
\vskip 4mm
\begin{center}
\begin{tabular}{lllcl}
\hline
Star&Comparison&Observation period& No.\ of nights&filters\\
\hline
TZ Aur  &  BD $+$41 1609     & 2453329 -- 2453358& 13&$BVR_CI_C$\\
BH Aur  &  GSC 02397-00378 & 2453743 -- 2453762 & 12& $VR_CI_C$\\
TW Lyn &  GSC 02971-00853 &	2453361 -- 2453387  & 17&$BVR_CI_C$ \\
\hline
\end{tabular}
\end{center}
%\vspace*{-0.6cm}
\end{table}

\vskip 4mm
Data reduction was performed using standard IRAF\footnote{{\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.}
packages.  Instrumental magnitudes were transformed to the standard
$BVR_CI_C$ system by observing photometric standards in M67 (Chevalier \&
Ilovaisky, 1991).


\IBVSfig{10.5cm}{5709-f1.ps}{Differential $V$, $B-V$, $V-R_C$ and $V-I_C$
light and colour curves of TZ Aur}
\IBVSfigKey{5709-f1.ps}{TZ Aur}{folded light curve}
\IBVSfig{10.5cm}{5709-f2.ps}{Differential $V$, $V-R_C$ and $V-I_C$ light
and colour curves of BH Aur}
\IBVSfigKey{5709-f2.ps}{BH Aur}{folded light curve}
\IBVSfig{10.5cm}{5709-f3.ps}{Differential $V$, $B-V$, $V-R_C$ and $V-I_C$
light and colour curves of TW Lyn}
\IBVSfigKey{5709-f3.ps}{TW Lyn}{folded light curve}

Our photometric data available electronically from the IBVS website list
the $BVR_CI_C$ magnitude differences between the variable and the
comparison. Standard magnitudes of the comparison stars are available only
for TZ Aur in $UBV$ bands (Stepien, 1972).  The constancy of the
brightness of the comparison stars was checked by measuring magnitude
differences to 3-6 other stars in our field of views. The rms. scatter of
these data is typically less than 0.01 mag. in each band which equals to
the rms scatter of the Fourier fit of the light curves of the variables.
The $V$ light curves and the $B-V$, $V-R_C$ and $V-I_C$ colour curves of
the three stars are plotted in Figs. 1-3.

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

\begin{table}[b!]
\normalsize
\centerline{Table 2.  Fourier parameters and normal maximum timings  of the $V$ light curves}
\begin{center}
\vskip 4mm
\begin{tabular}{l@{\hspace{2pt}}c@{\hspace{2pt}}cccccccccc}
\hline
Star&$T_0$ 
[HJD]&P$^*$&A1&R$_21$&R$_31$&R$_41$&R$_51$&$\varphi_{21}$&$\varphi_{31}$&$\varphi_{41}$&$\varphi_{51}$\\
&$-$2453000&[d]&[mag]&&&&&&&&\\
%\multicolumn{2}{c}{$P_\mu$} & Type \\
\hline
TZ Aur &343.622&0.3916746 &  0.441  &0.560  &0.349  &0.238  &0.152  &2.359  &5.094  &1.416  &4.174\\
BH Aur&755.264&0.4560898  &  0.316  &0.532  &0.326  &0.171  &0.101  
&2.606  &5.447  &2.057  &4.707\\
TW Lyn&375.551&0.4818600 &  0.344  &0.552  &0.343  &0.195  &0.110  &2.558  &5.358  &1.992  &4.658\\
\hline
\multicolumn{7}{l}{\footnotesize{$^*$Taken from the GCVS (Kholopov et al., 1985).}}&&&&&\\
\end{tabular}
\end{center}
\end{table}
\vskip 2mm

Spectroscopic [Fe/H]  values from the literature (transformed for the metalicity 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 3.

The relative absolute magnitudes of the three stars estimated from the Fourier 
parameters  using the first equation of Table 6.  of Kov\'acs \& Walker  (2001) indicate slight brightness differences between the stars. TW Lyn is the brightest and TZ Aur is the faintest, but the difference between their $M_V$ is only 0.08 mag. 

\begin{table}[]
\normalsize
\begin{center}
\centerline{Table 3. Spectroscopic and ,photometric' [Fe/H] values}
\vskip 3mm
\begin{tabular}{llll}
\hline
Star&[Fe/H] spect.& ref.& [Fe/H] phot.\\
\hline
TZ Aur &$-0.60$&Layden (1994)                &$-0.30$\\
           &$-0.63$&Suntzeff et al. (1994)      &           \\
BH Aur&$+0.14$&Fernley \& Barnes (1997)&$-0.17$\\
TW Lyn&$-1.03$&Layden (1994)                &$-0.43$\\
           &$-0.09$&Fernley \& Barnes (1997)&           \\
\hline
\end{tabular}
\end{center}
\end{table}

The financial support of OTKA grants T-043504, and T-048961 is acknowledged.

\IBVSedata{5709-t4.txt}
\IBVSdataKey{5709-t4.txt}{BH Aur}{photometry}
\IBVSedata{5709-t5.txt}
\IBVSdataKey{5709-t5.txt}{BH Aur}{photometry}
\IBVSedata{5709-t6.txt}
\IBVSdataKey{5709-t6.txt}{BH Aur}{photometry}
\IBVSedata{5709-t7.txt}
\IBVSdataKey{5709-t7.txt}{TW Lyn}{photometry}
\IBVSedata{5709-t8.txt}
\IBVSdataKey{5709-t8.txt}{TW Lyn}{photometry}
\IBVSedata{5709-t9.txt}
\IBVSdataKey{5709-t9.txt}{TW Lyn}{photometry}
\IBVSedata{5709-t10.txt}
\IBVSdataKey{5709-t10.txt}{TW Lyn}{photometry}
\IBVSedata{5709-t11.txt}
\IBVSdataKey{5709-t11.txt}{TZ Aur}{photometry}
\IBVSedata{5709-t12.txt}
\IBVSdataKey{5709-t12.txt}{TZ Aur}{photometry}
\IBVSedata{5709-t13.txt}
\IBVSdataKey{5709-t13.txt}{TZ Aur}{photometry}
\IBVSedata{5709-t14.txt}
\IBVSdataKey{5709-t14.txt}{TZ Aur}{photometry}



\references

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

Epstein, I., 1969,  {\it AJ}, {\bf 74}, 1131

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

Fitch, W.S., Wisniewski, W.Z, Johnson, H.L., 1966, {\it Comm.\ Lunar and
Planet.\ Lab.}, {\bf Vol 5.}, No 71

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

Jurcsik, J., S\'odor, \'A., V\'aradi, M., Szeidl, B., Washuettl, A., et
al., 2005, {\it A\&A}, {\bf 430}, 1049

Jurcsik, J., Szeidl, B., S\'odor, \'A., D\'ek\'any, I., Hurta, Zs., et
al., 2006, {\it AJ}, {\bf 132}, 61

Kholopov, P.N., et al., 1985, {\it General Catalogue of Variable Stars},
Moscow: Nauka Publishing House, 1988, 4th ed., edited by Kholopov, P.N.;
and 2004 web edition ({\tt http://www.sai.msu.su/groups/cluster/gcvs/})

Kov{\'a}cs, G., \& Walker, A., 2001, {\it A\&A}, {\bf 371}, 579

Layden, A., 1994, {\it AJ}, {\bf 108}, 1016

Schmidt, E.G., Chab, J.R., Reiswig, D.E. 1995, {\it AJ}, {\bf 109}, 1239

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

Stepien,  K., 1972, {\it Acta Astron.}, {\bf  22}, 175

Sturch, C.R.,  1966, {\it ApJ}, {\bf 143}, 774

Suntzeff, B.N., Kraft, R.P., Kinman, T.D.,  1994, {\it ApJ Suppl.\ Ser.}, 
{\bf 93}, 271

\endreferences

{\sc Corrected version, Thu Dec 14 09:11:40 MET 2006}

\end{document}
