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\input ibvs2.sty

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\IBVShead{5772}{17 May 2007}

\IBVStitletl{GSC 3377-0296 is a New Short-Period}{ Eclipsing RS CV\lowercase{n} Variable}

\IBVSauth{Lloyd, C.$^{1}$; Bernhard, K.$^{2,4}$; Monninger, G.$^{3,4}$}

\IBVSinst{Department of Physics and Astronomy, Open University, Milton Keynes MK7 6AA, UK; \\ \indent e-mail: {\tt C.Lloyd@open.ac.uk}}
\IBVSinst{A--4030 Linz, Austria; e-mail: {\tt klaus.bernhard@liwest.at}}
\IBVSinst{D--75050 Gemmingen, Germany; e-mail: {\tt gerold.monninger@online.de}}
\IBVSinst{Bundesdeutsche Arbeitsge\-mein\-schaft f\"{u}r Ver\"{a}nderliche 
Sterne e.V. (BAV), Munsterdamm 90,\\ \indent D--12169~Berlin, Germany}

\IBVStyp{  RSCVn  }

\IBVSkey{RSCVn, near-contact system, eclipsing binary, CCD photometry}

\IBVSabs{GSC 3377-0296 is a new eclipsing RS CVn variable, which has been}
\IBVSabs{discovered in the ROTSE1 database. A very short period of 0.4224672}
\IBVSabs{days has been determined from the available ROTSE1 data}
\IBVSabs{and our BVR photometry in 2006 and 2007. Large}
\IBVSabs{changes in the light curve occur on timescales of a few weeks.}


\SIMBADobjAlias{1RXS J064117.0+464904}{GSC 3377-0296}

\begintext

During a programme of optical identification of X-ray sources the uncatalogued variable, NSVS 4620766 in the ROTSE1
database (Wozniak et al., 2004), has been found to be coincident the variable X-ray source 1RXS J064117.0+464904 from
the ROSAT all-sky survey bright source catalogue (Voges et al., 1999, Fuhrmeister \& Schmitt 2003). The variable lies
within the 10\arcs\ uncertainty in the position of the X-ray source. The star is also identified as GSC 3377-0296 and is
catalogued by 2MASS at 06\hr41\mm16\fsec76 +46\deg49\arcm09\farcs0 (2000). Further details of the programme are
presented in Bernhard et al.\ (2005) and Bernhard \& Frank (2006).  GSC 3377-0296 has $V=12.32$ and $B-V=0.83$
transformed from the Tycho-2 catalogue (H\o g et al., 2000), the Tycho Input Catalogue, revised version gives $V=11.80$
(Egret et al., 1992), the 2MASS catalogue gives $J-K = 0.676$ (Cutri et al., 2003). The star is a high proper-motion
object (Kislyuk et al., 1999; Zacharias et al., 2004).

Further observations were made using both a 20-cm Schmidt--Cassegrain telescope and a Starlight XPress SX CCD camera
with $BVR$ filters in Linz, Austria and a 34-cm Cassegrain telescope with a CCD camera SBIG ST-6 and a $V$ filter in
Gemmingen, Germany.  The comparison star used was GSC 3377-0179. No reliable magnitude estimates exist for this star.
The Tycho-2 magnitudes are most probably wrong, as these contradict other available photometric information.  The check
stars were GSC 3377-0285 and GSC 3377-0811, which were found to be constant within $< 0.02$ mag.

The following primary minima were observed in 2006 and 2007:

\begin{table}[h] 
\centerline{\normalsize Table 1: Times of primary minima of GSC 3377-0296 (HJD 245\dots)} 
\vskip 3mm
\begin{center}
\begin{tabular}{lcll}
\hline
minimum time & filter & observer & $O-C$ (d) \\
\hline
4085.5907 (2) & $V$ & Monninger & $-0.0003$ \\
4092.3513 (2) & $V$ & Monninger & $+0.0008$ \\
4096.5776 (2) & $V$ & Monninger & $+0.0024$ \\
4171.3497 (3) & $V$ & Bernhard & $-0.0021$ \\
\hline
\end{tabular}
\end{center}
\end{table}

\IBVSfig{7.5cm}{5772-f1.ps}{ROTSE1 light curve of GSC 3377-0296 folded with a period 0.4224672 days}
 \IBVSfigKey{5772-f1.ps}{GSC 3377-0296}{light curve}

Figures in brackets denote rms errors in units of the last decimal, $O-C$ values were calculated with the ephemeris
given below.

A Fourier analysis of all the available data including TASS (http://www.tass-survey.org/)  and ROTSE1 was performed to
search for periodicity of the light variations. The following ephemeris can be derived from the analysis with the
algorithm Period04 (Lenz \& Breger, 2005):
 $$
 \begin{array}{r@{}r@{}l}
 {\rm HJD_{MinI}} = 2454085.591 & {} + 0\fday422467 & {} \times E.\\
 \pm 3 & \pm 1 \\
 \end{array}
 $$

The folded ROTSE1 light curve is shown in Figure 1, which identifies GSC 3377-0296 with a very short period and heavily
spotted RS CVn type star. The ROTSE1 dataset (April 1999--March 2000) was divided into two parts of equal length to
search for secondary variations (April 1999--October 1999: filled circles; November 1999--March 2000: open circles).  It
can be seen, that the shape of the light curve varies between phase 0.2 and 0.5 due to the changing activity of star
spots.

The folded light curve of our observations with $V$ filters (G. Monninger: 15--27 December 2006, filled circles;  K.
Bernhard: 4--15 March 2007) is given in Figure 2. Small offsets have been applied to G. Monningers data set as part
of the fitting process.

It shows distinct variations within the time span of four months from phase 0.4 to 0.8. Changes of the light curve were
noticed even within a week near phase 0.7 (see filled circles). Considering the ROTSE1 data, large parts of the light
curve (phase 0.2 to 0.8)  are affected by stellar activity, which suggests, that there could be two active longitudes
similar to other RS CVn variables (e.g. Berdyugina and Tuominen, 1998).

The folded $\Delta V, \Delta(B-V), \Delta(V-R_C)$ light curves, relative to GSC 3377-0179, of the filtered observations
in March 2007 are shown in Fig 3.
The $B-V$ and $V-R_C$ colour differences between the variable and the comparison are relatively small, and indicate a
slight reddening of the star, when it enters the minimum of the spotted light curve at phase 0.63.

\IBVSfig{9cm}{5772-f2.ps}{Our $V$-band observations from 15 December 2006--15 March 2007 relative to GSC 3377-0179}
 \IBVSfigKey{5772-f2.ps}{GSC 3377-0296}{light curve}

\IBVSfig{10cm}{5772-f3.ps}{ Folded $\Delta V, \Delta(B-V)$ and $\Delta (V-R_C)$ light curves of GSC 3377-0296, March
2007}
 \IBVSfigKey{5772-f3.ps}{GSC 3377-0296}{light curve}

\vspace*{-24pt}
The magnitude difference between the maximum and this minimum, determined by low order polynomial fitting, is for the
$B$ band about 0.14 mag, for the $V$ and $R_C$ band only 0.12 and 0.10 mag. This is in good agreement with data from
literature, where a $\Delta R/\Delta V$ value of 0.90 for active stars has been determined (Drake, 2006).

The median magnitude of the NSVS data of the variable is 0.87 mag brighter than of the comparison star GSC 3377-0179,
which is similar to the respective value of our observations in $R_C$ band (0.96 mag) and $V$ band (0.89 mag).

The variability type RS CVn is also supported by the X-ray identification and the 2MASS colours $J-H = 0.54$ and $H-K =
0.14$, which suggest a spectral type of K3.

The period of 0.4224672 days is very short for an RS CVn star. It is shorter than the periods of all 206 binary systems
listed in the second edition of the catalogue of chromospherically active binary stars (shortest period: XY UMa,
0.4789944 days; Strassmeier et al., 1993).

Although the period is similar to that of XY UMa the light curve is rather different (Collier Cameron \& Hilditch 1997),
and suggests a smaller, near-contact system. The light curve is similar to the near-contact binary GR Tau (P=0.42985
days Zhang et al., 2002), although this class of star is limited to spectral types A--F and does not show RS CVn-like
chromospheric activity. GSC 3377-0296 clearly shows evidence of cool spots, probably at two opposite longitudes, but is
also probably a near-contact system.

{\bf Acknowledgements:} This research has made use of the SIMBAD and VizieR databases operated at the Centre de
Donn\'ees Astronomiques (Strasbourg) in France.

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\endreferences

\end{document}
