system, but also a long cycle in time scale of several hundreds of days (Fig.1). The system is fainter in the $V$-band than in the $I$-band and the eclipses are deeper in $V$.

We used the generalized Lomb-Scargle (GLS) periodogram to obtain the orbital frequency in our data. This algorithm was introduced by and uses the principle of the & @1982ApJ...263..835S periodograms with some modifications, such as the addition of a displacement in the adjustment of the fit function and the consideration of measurement errors. Compared with the classical periodogram, it gives us more accurate frequencies and a better determination of the amplitudes. We obtained P$_{\rm o} =  24\fd7992 \pm \rm 0\fd0024.$

With the above period we phased the $I$-band light curve. This allowed us to select the deeper data points in the primary eclipse, corresponding in this system to the usually more deeper eclipse, for every data segment that is colored in Fig.1. These data points were analyzed with the cycle-number technique for linear-ephemerides [@2005ASPC..335....3S] and the following improved ephemeris for the primary eclipse was derived (Fig.2): $$\begin{aligned}
%\rm HJD&=&\rm (245\,6695\fd756 \pm \rm 0\fd058) + \rm (24\fd80091 \pm \rm 0\fd00044)\, E
\rm HJD&=&\rm (245\,6695\fd918 \pm \rm 0\fd059) + \rm 