  We carry out a re-analysis of the photometric data in Cousin RI bands which
was taken under the Nainital Microlensing Survey during 1998 to 2002 with the
aim to detect gravitational microlensing events in the direction of M31. Here,
we do photometric analysis of a faint W UMa binary CSS_J004259.3+410629
identified in the target field. The orbital period of this star is found to be
0.266402+/-0.000018 day. The photometric mass ratio, q, is found to be
0.28+/-0.01. The photometric light curves are investigated using the
Wilson-Devinney code and absolute parameters are determined using empirical
relations which provide masses and radii of the binary as M1 = 1.19+/-0.09
Msun, M2 = 0.33+/-0.02 Msun and R1 = 1.02+/-0.04 Rsun, R2 = 0.58+/-0.08 Rsun
based on the Rc band data. Almost similar values are found by analysing Ic band
data. From the photometric light curve examination, the star is understood to
be a low mass-ratio over-contact binary of A-subtype with a high fill-out
factor of about 47%. The binary system is found to be located approximately at
a distance of 2.64+/-0.03 kpc having a separation of 2.01+/-0.05 Rsun between
the two components.
