Physical parameters and orbital period variation of a newly discovered
  cataclysmic variable GSC 4560-02157
  GSC 4560-02157 is a new eclipsing cataclysmic variable with an orbital period
of $0.265359$ days. By using the published $V-$ and $R-$band data together with
our observations, we discovered that the $O-C$ curve of GSC 4560-02157 may
shows a cyclic variation with the period of $3.51$ years and an amplitude of
$1.40$ min. If this variation is caused by a light travel-time effect via the
existence of a third body, its mass can be derived as
$M_{3}sini'\approx91.08M_{Jup}$, it should be a low-mass star. In addition,
several physical parameters were measured. The colour of the secondary star was
determined as $V-R=0.77(\pm0.03)$ which corresponds to a spectral type of K2-3.
The secondary star's mass was estimated as $M_{2}=0.73(\pm0.02)M_{\odot}$ by
combing the derived $V-R$ value around phase 0 with the assumption that it
obeys the mass-luminosity relation of the main sequence stars. This mass is
consistent with the mass$-$period relation of CV donor stars. For the white
dwarf, the eclipse durations and contacts of the white dwarf yield an upper
limit of the white dwarf's radius corresponding to a lower limit mass of
$M_{1}\approx0.501M_{\odot}$. The overestimated radius and previously published
spectral data indicate that the boundary layer may has a very high temperature.
