\documentstyle[twoside, ibvs2, epsf]{article}


\begin{document}

\IBVShead{4922}{20 July 2000} 

\IBVStitle{B Photometry of Romano's Star in M\,33}

\IBVSauth{Kurtev, R.$^{1}$; Sholukhova, O.$^{2}$; Borissova, J.$^3$; Georgiev, L.$^4$}

\IBVSinst{Department of Astronomy, Sofia University, BG\,--\,1164 Sofia, Bulgaria;
email: kurtev@phys.uni-sofia.bg}

\IBVSinst{Special Astrophysical observatory, Nizhnij Arkhyz, Karachai-Cherkessia 357147, Russia}

\IBVSinst{Institute of Astronomy, Bulgarian Academy of Sciences,
72~Tsarigradsko chauss\`ee, BG\,--\,1784 Sofia, Bulgaria}

\IBVSinst{Instituto de Astronom\'{\i}a, Universidad Nacional Aut\'onoma de M\'exico, M\'exico}

\IBVSobj{Romano's star in M33}

\begintext

We present the light curve of Luminous Blue Variable candidate star
GR\,290 (Romano's star) in M\,33 (Humphreys \& Davidson 1994). The
observational basis of this study is a sample of photographic plates of
M\,33 from the collection of the Bulgarian National Astronomical
Observatory --- Rozhen. All plates have been taken with the 2-m RCC
$f/8$ Rozhen reflector.

We used 25 $B$-plates, $30 \times 30$~cm (103aO, IIaO and ORWO ZU\,21
emulsions, GG\,385 glass filter). The plates were taken from November,
1982 to October, 1990. Julian days of observations are presented in
Table~1. The plate scale is 12.8 arcsec\,mm$^{-1}$ and the area
covered is 1\deg$\times$1\deg. The whole image of M\,33 fits in each
plate.

The measurements have been made with a MF-4 densitometer with a
constant diaphragm in the Astronomical observatory of the Sofia
University. At least four estimations of sky background for each star
were obtained and then averaged value was used. The calibration curves
have been constructed using the photoelectric sequence of Sandage \&
Johnson (1974). Then they have been fitted by the least squares with
the most appropriated polynomials. For each plate standard deviations
of measurements are presented in Table~1.

We present also CCD $B$-magnitude of Romano's star. Data were obtained
on Special Astrophysical Observatory --- SAO (Russia) with 1024$\times$1024 
CCD camera on 0.6-m Zeiss telescope (Vlasiuk 1997). The seeing
during the observations was 2--3 arcsec. The scale was 0.84
arcsec/pixel, resulting in a field size of about 8 arcmin. Photometry
of the program frame was carried out by PSF-fitting using {\sc
iraf/daophot}. Transformation to the standard system is based on
average photographic $B$-magnitudes of reference stars (A--L in Fig.~1)
taken from the best five Rozhen $B$ plates. Average magnitudes and root
mean squares (r.m.s.)\ for these stars are given in Table~2.

The results of our photometry are given in Table~1. The light
curve of Romano's star is presented in Fig.~2. Open circles
represent original Romano's observations transferred to the Johnson $B$
system (Romano 1978), photographic $B$-magnitudes from Rozhen 2-m RCC
telescope are given with open diamonds, and the CCD $B$-magnitude from
0.6-m telescope --- with open triangle. It is seen that Romano's star
presents two broad maxima within a few years around 1970 and 1990. The
derived mean cycle for the whole data set (Romano's + ours), using
PDM method is about 6250 days.

\IBVSfig{9cm}{4922-f1.eps}{CCD $B$ image of the area around the
Romano's star. North is up and East is to the left. Reference stars
A--L from secondary photographic sequence are shown.}

\IBVSfig{9cm}{4922-f2.eps}{The long term $B$ light curve of the
Romano's star. Open circles represent original Romano's observations
transferred to $B$-magnitudes, open diamonds --- 2-m Rozhen
observations, and open triangle --- 0.6-m SAO observation.}

\begin{table}
\begin{center}
\caption{Photometry in $B$ band of Romano's star in M\,33}
\begin {tabular}{l@{~}cc|l@{~}cc|l@{~}cc|l@{~}cc}
\hline
JD & \lower6pt\hbox{$B$} & \lower6pt\hbox{$\sigma(B)$} & JD &
\lower6pt\hbox{$B$} & \lower6pt\hbox{$\sigma(B)$} & JD &
\lower6pt\hbox{$B$} & \lower6pt\hbox{$\sigma(B)$} & JD &
\lower6pt\hbox{$B$} & \lower6pt\hbox{$\sigma(B)$} \\[-3pt]
$244\dots$ & & & $244\dots$ & & & $244\dots$ & & & $244\dots$ & & \\
\hline
5286 & 17.16 & 0.15 & 5591 & 17.40 & 0.16 & 6707 & 17.46 & 0.16 & 8177 & 16.88 & 0.18 \\
5295 & 17.25 & 0.15 & 5623 & 17.51 & 0.23 & 6707 & 17.51 & 0.16 & 8180 & 16.96 & 0.17 \\
5296 & 17.19 & 0.23 & 5625 & 17.61 & 0.16 & 6708 & 17.30 & 0.07 & 8180 & 16.99 & 0.13 \\
5297 & 17.24 & 0.25 & 5702 & 17.11 & 0.08 & 6708 & 17.52 & 0.10 & 8180 & 16.89 & 0.12 \\
5588 & 17.35 & 0.23 & 5929 & 17.30 & 0.08 & 6709 & 17.49 & 0.08 & & & \\
5588 & 17.34 & 0.26 & 5968 & 17.38 & 0.09 & 6738 & 17.45 & 0.11 & & & \\
5590 & 17.55 & 0.20 & 6435 & 17.55 & 0.08 & 6738 & 17.32 & 0.17 & & & \\
\hline
\end{tabular}
\end{center}

\bigskip

\begin{center}
\caption{Average $B$-magnitudes and r.m.s.\ of reference stars}
\vskip12pt
\begin {tabular}{lll|lll}
\hline
St & \multicolumn{1}{c}{$\langle B\rangle$} & r.m.s. & St & \multicolumn{1}{c}{$\langle B\rangle$} & r.m.s. \\
\hline
A & 15.49 & 0.18 & F & 17.33 & 0.06 \\
B & 15.79 & 0.07 & G & 17.86 & 0.03 \\
C & 16.48 & 0.13 & H & 16.33 & 0.16 \\
D & 16.35 & 0.10 & K & 17.10 & 0.19 \\
E & 17.22 & 0.13 & L & 17.91 & 0.07 \\
\hline
\end{tabular}
\end{center}
\end{table}

{\it Acknowledgements:} It is a pleasure to thank Prof.~G.~Ivanov,
Dr.~P.~Kunchev and Dr.~Ts.~Georgiev for letting us use their plates of
M\,33. This research was supported in part by the Bulgarian National
Science Foundation grant under contract No.\ F-812/1998 with the
Bulgarian Ministry of Education and Sciences. O. Sholukhova thanks for
support RFBR grant No.\ 00-02-16588.

\references

Humphreys, R., Davidson, K., 1994, {\it PASP}, {\bf 106}, 1025

Romano, G., 1978, {\it A\&A}, {\bf 67}, 291

Sandage, A., Johnson, H., 1974, {\it ApJ}, {\bf 191}, 63

Vlasiuk, V., ed., 1997, Report SAO, 33

\end{document}

