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\IBVShead{4365}{9 August 1996}

\title{THE NEW OVERCONTACT ECLIPSING BINARY STAR NSV\,07457}

\begintext

Following the program initiated by the Grup d'Estudis Astronomics in 1995 
in cooperation with the Esteve Duran Observatory Foundation, for observing 
poorly studied variable stars, NSV\,07457 was monitored in the V band for 
13 nights, from 24 March 1996 to 26 May 1996, using a CCD camera attached 
to the 0.3-m telescope at L'Estelot Observatory in L'Ametlla de Mar (Spain). 
To perform differential photometry, GSC\,3497.0310 and GSC\,3497.0239 were 
chosen as comparison and check stars, respectively.

Geyer et al. (1955) indicated that NSV\,07457 (=BD\,+50\degr 2255 = 
CSV\,007268 = BV\,0103)  was a possible RR Lyrae type variable with a 
photographic magnitude variation 
from 9\fm 7 to 10\fm 4. The star can be unambiguously identified with 
GSC\,3497.0263, an object with a photovisual magnitude (PAL-V1 filter) of 
10.07$\pm$0.40. 

The present observations allowed to determine that NSV\,07457 is not an RR 
Lyrae but an overcontact eclipsing binary star with a period over 11 hours.
Primary minimum is an occultation with a depth of 0\fm 54 and secondary 
minimum is a transit with a depth of 0\fm 51. An O'Connell effect that amounts 
to $\Delta$m=Max.\,I$-$Max.\,II=$-$0.03 was also detected, where Max.\,I is at 
phase 0.25 and Max.\,II at phase 0.75.

 The following ephemeris was also derived:
\vskip 1mm
\centerline{Min.\,I = HJD\,2450177.4767 + 0\fd 41906 $\times$ E}
\hspace*{70mm}$\pm$0.0004 \ \ $\pm$0.00003
\vskip 1mm

A preliminary model of NSV\,07457 was computed using Binary Maker 2.0 
(Bradstreet, 1993), applying the same analysis method described by 
Gomez-Forrellad and Garcia-Melendo (1996) after converting the phase curve 
to 200 normal points. The O'Connell effect and light curve asymmetries that 
frequently appear in overcontact binary systems are currently interpreted as 
bright or dark areas on the binary components. In this case, an initial 
unspotted solution was obtained, and finally a spotted model was recomputed.

Initially the following parameters were fixed to obtain the photometric 
solution: a mean surface temperature T$_1$=6000K, according to the spectral 
type G0 given by Kholopov (1982), and gravity darkening coefficients 
g$_1$=g$_2$=0.32 and bolometric albedos A$_1$=A$_2$=0.5, which correspond to 
stars with convective external layers. Limb darkening coefficients x$_1$ and 
x$_2$ were set to 0.6. Due to the lack of spectroscopic information about mass 
ratio, a search for the solution was carried out from q=3.0 to q=4.8 in mass 
ratio steps of 0.2. 

Once the unspotted solution was reached, it was refined invoking a 
single spot. No further attempt was made to introduce more spots to improve 
light curve fitting. A colatitude of 90\degr\ was fixed. Spot radius, 
colongitude and temperature factor were adjusted. It was found that light 
curve was best modeled with a hot spot on the secondary component. Elements 
of the best solution are given in Table 1. Table 2 lists spot parameters. 
Figure 1 shows the light curve of NSV\,07457, and Figure 2 depicts the synthetic 
light curve superimposed on normal points.
\vfill \eject

\centerline{2}
\vskip 1cm
\epsfysize=10cm
\centerline{\epsffile{4365-f1.ps}}
\centerline{Figure 1}
\epsfysize=10cm
\centerline{\epsffile{4365-f2.ps}}
\centerline{Figure 2}
\vfill \eject

\centerline{3}
\vskip 1mm
\centerline{Table 1}
\vskip 1mm
\medskip
\centerline{mass ratio = 3.8 $\pm$ 0.2}
\centerline{i = 79\fdg 0 $\pm$ 2\fdg 0}           
\centerline{fillout = 0.25 $\pm$ 0.10}
\medskip

\hspace*{4cm}  Omega$_1$=Omega$_2$=7.499$\pm$0.200

\hspace*{4cm}  a$_g$=0.543$\pm$0.011\ \ \ a$_s$=0.315$\pm$0.001

\hspace*{4cm}  b$_g$=0.515$\pm$0.010\ \ \ b$_s$=0.274$\pm$0.001

 \hspace*{4cm} c$_g$=0.475$\pm$0.008\ \ \ c$_s$=0.262$\pm$0.001

 \hspace*{4cm} d$_g$=0.633$\pm$0.005\ \ \ d$_s$=0.367$\pm$0.005

 \hspace*{4cm} g$_1$=g$_2$=0.32 

 \hspace*{4cm}  x$_1$=x$_2$=0.6 

 \hspace*{4cm}  A$_1$=A$_2$=0.5

 \hspace*{4cm}  T$_1$=6000K\ \ \ T$_2$=6280K$\pm$100K

 \hspace*{4cm}  L$_1$=0.720$\pm$0.01\ \ \  L$_2$=0.280$\pm$0.007
\vskip 3mm
\centerline{Table 2}
\vskip 1mm
\begin{center}
\begin{tabular}{lc}
\hline
 Colatitude = 90\degr\\
 Colongitude = 45\degr\\
 Spot Radius = 20\degr\\
 T$_f$=1.14\\
\hline
\end{tabular}
\end{center}
\vskip 1cm
             
   
\beginauthors
Jaime NOMEN-TORRES                      
Grup d'Estudis Astronomics          
Apartado 9481                      
08080 Barcelona                    
Spain                                 
e-mail:jnomen@astro.gea.cesca.es   
\vskip 2mm    
\authorsrightcol   
Enrique GARCIA-MELENDO
Esteve Duran Observatory
El Montanya - Seva
08553 SEVA
(Barcelona)
Spain
e-mail:duranobs@astro.gea.cesca.es
\endauthors


\references

Bradstreet, D. H., 1993, Binary Maker 2.0 User Manual, Contact Software,
 Norristown, Pennsylvania

Geyer, E., Kippenhahn, R., Strohmeier, W., 1955, {\it KVB}, No.\,11

Gomez-Forrellad, J. M., Garcia-Melendo, E., 1996, {\it IBVS}, No.\,4364

Kholopov, P. N., editor, 1982, New Catalogue of Suspected Variable Star,
 Moscow

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