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\IBVShead{6028}{28 June 2012}

\IBVStitle{TYC\,4031-791-1 - a new eclipsing binary of Algol type}

\IBVSauth{Ga{\l}an, C.$^1$; Tomov, T.$^1$; \'Swierczy\'nski, E.$^1$; Wychudzki, P.$^2$; Bro\.zek, T.$^1$;\\ I{\l}kiewicz, K.$^1$; Miko{\l}ajewski, M.$^1$; Drozd, K.$^1$}

\IBVSinst{Toru\'n Centre for Astronomy, Nicolaus Copernicus University, ul. Gagarina 11, 87-100 Toru\'n, Poland, e-mail: cgalan@astri.uni.torun.pl}
\IBVSinst{Olsztyn Planetarium and Astronomical Observatory, Al. Marsza{\l}ka J. Pi{\l}sudskiego 38, 10-450 Olsztyn, Poland}

\SIMBADobjAlias{TYC 4031-791-1}{GSC 04031-00791}
\IBVStyp{  EA  }
\IBVSkey{new eclipsing binary, photometry, spectroscopy}
\IBVSabs{We report on the discovery of TYC 4031-791-1 as an eclipsing binary}
\IBVSabs{of Algol type which shows primary and secondary eclipses with period}
\IBVSabs{P_orb approx. 6.68 days. The system is composed of two, perhaps similar}
\IBVSabs{stars of spectral type around B5 on slightly eccentric orbit.}

\begintext

TYC\,4031-791-1 is an 11th magnitude star located in the constellation
Cassiopeia in close proximity (8.2 arcmin) to the long-period eclipsing
binary AZ\,Cas ($P_{\mathrm{orb}} \approx 9.3$\,yr).  We have monitored the
photometric variability of AZ\,Cas since August\,2003 with the 60-cm
Cassegrain telescope at Piwnice Observatory
(53.0943\,$^{\circ}$N,\,18.5532\,$^{\circ}$E).  In 2005 we switched from
photomultiplier to CCD (SBIG-STL-1001) and we needed new comparison stars
for photometry.  TYC\,4031-791-1 was one among many in the group of stars
that have been tested to establish the sequence of comparison stars for
AZ\,Cas (Galan\,et\,al.~2012), suitable for the narrow field of view of our CCD
camera ($11.4' \times 11.4'$).  We collected differential light curves for
TYC\,4031-791-1 with respect to all comparison stars during the last 7 years. 
We have observed deviations with similar amplitudes in all
($UBV(RI)_{\mathrm C}$) photometric bands (the $V$ light
curve is shown in Fig.\,1).

\IBVSfig{5.7cm}{6028-f1.eps}{The $V$ band differential light curve
of TYC\,4031-791-1 obtained with respect to BD+60$^{\circ}$303.  The data
collected at Piwnice Observatory are shown with filled circles.  Some of the
data, presented with open circles, have been obtained with the 25/250\,cm
Schmidt-Cassegrain telescope and a SBIG-ST-8XME CCD camera at the Olsztyn
Planetarium and Astronomical Observatory.}
\IBVSfigKey{6028-f1.eps}{TYC 4031-791-1}{light curve}

We checked that this star has not been reported variable in the GCVS
catalogue (Samus\,et\,al.~2012) or in any other electronically available
database.  Assuming that the observed phenomenon is caused by eclipses,
we searched for the orbital period using the {\tt{PerSea 2.6}} tool
(a program written by Gracjan Maciejewski:\\ \noindent
{\tt{http://www.astri.uni.torun.pl/$\sim$gm/software.html}}), in which the
ANOVA method for optimal period search by Schwarzenberg-Czerny~(1996) is
implemented.  We have obtained the orbital period  of $6.6827 \pm
0.0002$ days.  Using the method of Kwee $\&$ van\,Woerden~(1956) we have
determined the time of primary minimum and obtained the ephemeris:

\begin{equation}
 JD_{\mathrm{mid-ecl}} = 2453650.327 (\pm 0.015) + 6.6827 (\pm 0.0002) \times E
\end{equation}

The $BVR_{\mathrm C}$ light curves phased with the orbital period are shown in
Figure\,2.  The secondary minimum occurs at phase $0.445 \pm 0.003$ 
indicating that the orbit is slightly eccentric.  The minima are quite shallow
- the primary minimum is not deeper than 0\fmm2.  The second eclipse is
shallower by about only 0\fmm02.  The depths of the eclipses seem to be
independent or depend very weakly on the photometric band.  This suggests
that the photospheres of the system components may have similar effective
temperatures.

\IBVSfig{8.5cm}{6028-f2.eps}{$BVR_{\mathrm C}$ light curves of
TYC\,4031-791-1 phased with the orbital period.}
\IBVSfigKey{6028-f2.eps}{TYC 4031-791-1}{light curve}

Fransworth~(1956) has reported B1 spectral type for TYC\,4031-791-1.  In
the spectrum obtained on Mar\,10,~2003 (Fig.\,3), the strongest 
features are the H${\alpha}$, He$\mathrm I$\,5876\AA\, and He$\mathrm
I$\,6677\AA\, absorption lines which confirms that star is of type B. 
However, the position of TYC\,4031-791-1 on the $U-B$, $B-V$ two-color 
diagram (Fig.\,4) indicates a somewhat later spectral type: B5 with an
accuracy of about 3 subtypes.  TYC\,4031-791-1 is strongly reddened by
interstellar matter -- the color excess is large: $E(B-V) = 0.72 \pm 0.12$. 
This explains the very strong DIBs (5780\,\AA\,, 5797\,\AA\,, 6284\,\AA\,,
6614\AA)\, and Na$\mathrm I$ interstellar doublet in the spectrum
(Fig.\,3).

\IBVSfig{5.5cm}{6028-f3.eps}{A medium resolution spectrum ($R
\sim 2000$) of TYC\,4031-791-1, obtained on Mar\,10,~2007 with the CCS
spectrograph on the 60/90-cm Schmidt-Cassegrain telescope at Piwnice
Observatory.}
\IBVSfigKey{6028-f3.eps}{TYC 4031-791-1}{other}

\IBVSfig{11cm}{6028-f4.eps}{Location of TYC\,4031-791-1 on the
$U-B$, $B-V$ color-color diagram (blue point with errorbars), constructed
with average out-of-eclipse magnitudes of the star: $m_{\mathrm
U}=11.66\pm0.06$, $m_{\mathrm B}=11.71\pm0.04$, $m_{\mathrm V}=11.16\pm0.03$
(Galan\,et\,al.~2012). The calibrations of Strai\v{z}ys (1977) for dwarfs ($+$) and
giants ($\times$) are shown as well. The red-dashed lines indicate the direction
of the interstellar reddening.}
\IBVSfigKey{6028-f4.eps}{TYC 4031-791-1}{other}

Additional photometric and spectroscopic observations are needed to constrain 
the system parameters further. We intend to obtain accurate multicolor
photometry of eclipses using our ephemeris and radial velocities with 
high-resolution spectra for further analysis.

\vskip 2mm
Acknowledgements: We thank K.\,Czart, B.\,Deka, S.\,Fr\c{a}ckowiak,
A.\,Karska, D.\,Kubicki, D.\,Puchalski, M.\,Radecki, P.\,R\'o\.za\'nski,
W.\,Tyrkin, M.\,Wi\c{e}cek, P.\,Wirkus, M.\,Starszak, O.\,Zio{\l}owska and
one unidentified student for their occasional contribution to the collection
of photometric data.

\vskip 0.5cm

\references

Fransworth, A.\,H., 1955, {\it ApJS}, {\bf 2}, 123 %\BIBCODE{1955ApJS....2..123F}

Galan, C., Tomov, T., Mikolajewski, M., et al., 2012, {\it IBVS}, No. 6027 

Kwee, K.\,K. $\&$ van Woerden, H., 1956, {\it BAN}, {\bf 12}, 327 %\BIBCODE{1956BAN....12..327K}

Samus, N.\,N., Durlevich O.\,V., Kazarovets E.\,V., 2012, {\it General Catalog of Variable Stars (GCVS database, Version 2012\,Jan)}, VizieR On-line Data Catalog B/gcvs %http://cdsarc.u-strasbg.fr/viz-bin/Cat?cat=B%2Fgcvs&

Schwarzenberg-Czerny, A., 1996, {\it ApJL}, {\bf 460}, 107 %\BIBCODE{1996ApJ...460L.107S}

Strai\v{z}ys, V., 1977, {``Multicolor Stellar Photometry''} (in Russian), MOKSLAS Publ., Vilnius  \BIBCODE{1977mspp.book.....S}

\endreferences

\IBVSedata{6028-t1.txt}
\IBVSdataKey{6028-t1.txt}{TYC 4031-791-1}{photometry}
\IBVSedata{6028-t2.txt}
\IBVSdataKey{6028-t2.txt}{TYC 4031-791-1}{photometry}


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