\documentstyle[twoside, epsf]{article}

\input ibvs2.sty

\begin{document}
\IBVShead{5021}{25 January 2001}

\IBVStitle{NSV 5904: a New W UM\lowercase{a} Eclipsing Binary}

\IBVSauth{Vandenbroere, J.; Martignoni, M.; Verrot, J.P.; Acerbi, F.}

\IBVSinsto{Group Europ\'een d'Observations Stellaires (GEOS), 
23 Parc de Levesville, 28300 Bailleau l'Ev\"{e}que, France\\ \indent
e-mail: j.vandenbroere@skynet.be, maxmartignoni@inwind.it, jp.verrot@wanadoo.fr, acerbifr@tin.it}

\SIMBADobj{NSV 5904} 
\IBVSabs{The variability of NSV 5904 was confirmed by means of visual,}
\IBVSabs{photoelectric and CCD measurements. The investigation of all available}
\IBVSabs{minima suggests a period of 0.326890 d.}

\begintext

NSV 5904 (GSC 3021 2642; 12\hr43\mm37\fsec22, +38\deg44\arcm16\farcs4;
2000.0) was first suspected to be a variable ranging from magnitude
11.2 to 12.0 (p) by Weber (1963). Since 1996, it has been visually
monitored by two GEOS observers (Vandenbroere and Verrot) whose
estimates confirmed the variability of the star showing an apparent
period of 0\fday16345 (Vandenbroere 1999).

Photoelectric measurements were performed at the Jungfraujoch
station on the basis of the collaboration between GEOS and Geneva
Observatory. Nine $BV$ points were obtained on two nights in December
1998 (``all-sky'' photometry, see Table~1). The very small amplitude
of the $B-V$ colour index suggested the eclipsing nature of NSV 5904.
The orbital period calculated from 20 visual minima was $0.3268885
\pm 0.00006$~d.

\begin{table}[hb]
\caption{The $V$ and $(B-V)_G$ photoelectric measurements of 
NSV 5904} 
\begin{center}
\begin{tabular}{cccc}
\hline
HJD & $V$ & $(B-V)_G$ & Phase \\
\hline
 2451170.5986 & 11.093 & +0.020 & 0.582 \\
 2451170.6118 & 11.005 & +0.010 & 0.622 \\
 2451170.6570 & 10.964 & $-0.015$ & 0.761 \\
 2451170.6875 & 11.084 & +0.002 & 0.854 \\
 2451172.6294 & 10.977 & $-0.011$ & 0.794 \\ 
 2451172.6530 & 11.091 & $-0.000$ & 0.867 \\
 2451172.6703 & 11.261 & +0.015 & 0.920 \\
 2451172.6912 & 11.463 & +0.038 & 0.983 \\
 2451172.7057 & 11.407 & +0.018 & 0.028 \\
\hline
\end{tabular}
\end{center}
\end{table}

After that, Martignoni made 228 CCD measurements of NSV 5904 in order
to obtain its photometric light curve (see Fig.~1). He used an
unfiltered CCD Seti 245C $378\times242$ attached to a 215-mm $f/5$
reflector at his private station in Busto Arsizio, Italy, and he
chose GSC 3021 2613 (11\fmm4) and GSC 3021 0451 (12\fmm9) as
comparison stars. The CCD light curve allowed him to discriminate
between the primary and secondary minima. A more accurate orbital
period was determined by means of 6 CCD and 16 new visual times of
minima together with the 20 times already published (Vandenbroere
1999). The result of the linear regression, giving a double weight
to the CCD times, is the following:
$$\begin{array}{r@{}r@{}l}
{\rm Min~I = HJD}~2450571.219 & {} + 0\fday326890 & {} \times E. \\
\pm0.003 & \pm0.000002 \\
\end{array}
$$
%\IBVSindexobj{GSC 3021 2613}
%\IBVSindexobj{GSC 3021 0451}


\newpage

\IBVSfig{7.95cm}{5021-f1.ps}{CCD unfiltered light curve of NSV 5904}

The CCD minima can be found in Table~2. Visual timings are regularly
published in the BBSAG bulletins or can be obtained from the
authors. Phases and $O-C$'s in Tables~1 and~2 are calculated in
respect with the above ephemeris.

\begin{table}[hb]
\vspace{-8pt}
\caption{CCD minima of NSV 5904}
\begin{center}
\begin{tabular}{clc}
\hline
HJD & \multicolumn1c{$E$} & $O-C$ \\
\hline
2451679.3732 & 3390 & $-0.0038$ \\
2451687.3840 & 3414.5 & $-0.0018$ \\
2451688.3639 & 3417.5 & $-0.0026$ \\
2451694.4142 & 3436 & +0.0002 \\
2451696.3730 & 3442 & $-0.0023$ \\
2451711.4138 & 3488 & +0.0015 \\
\hline
\end{tabular}
\end{center}
\vspace{-8pt}
\end{table}

Together with the $B$ and $V$ photoelectric measurements, we can
deduce from the CCD light curve that NSV 5904 varies from magnitude
10.96 to 11.47 ($V$-light) at primary minimum, with a secondary
minimum going to magnitude 11.40. The $(B-V)_G$ index of NSV 5904
varies very little around 0.01 which corresponds to a $B-V$
index of 0.78 after transformation to the $UBV$ system and assuming
luminosity class~V.

An attempt to model the system was made using the Binary Maker software
(Bradstreet 1993), but systematic deviations between observational
points and fitting curve were always found. A more sophisticated method
combined with multiwavelength observations should allow a better
description; at this purpose, the original measurements are available
from the IBVS website as 5021-t3.txt. \IBVSedata{5021-t3.txt}

\vskip-8pt

\references

Bradstreet, D.H., 1993, {\it Binary Maker 2.0 User Manual}, Contact Software, Norristown, PA 19401-5505, USA

Vandenbroere, J., 1999, {\it NC GEOS}, No.\ 894

Weber, R., 1963, {\it IBVS}, No.\ 21

\end{document}


