We present Roche tomograms of the secondary star in the dwarf nova system RU Pegasi derived from blue and red arm ISIS data taken on the 4.2-m William Herschel Telescope .
We have applied the entropy landscape technique to determine the system parameters and obtained component masses of M _ { 1 } = 1.06 M _ { \odot } , M _ { 2 } = 0.96 M _ { \odot } , an orbital inclination angle of i = 43 ^ { \circ } , and an optimal systemic velocity of \gamma = 7 \thinspace \hbox { $ \hbox { km } \thinspace \hbox { s } ^ { -1 } $ } .
These are in good agreement with previously published values .

Our Roche tomograms of the secondary star show prominent irradiation of the inner Lagrangian point due to illumination by the disc and/or bright spot , which may have been enhanced as RU Peg was in outburst at the time of our observations .
We find that this irradiation pattern is axi-symmetric and confined to regions of the star which have a direct view of the accretion regions .
This is in contrast to previous attempts to map RU Peg which suggested that the irradiation pattern was non-symmetric and extended beyond the terminator .

We also detect additional inhomogeneities in the surface distribution of stellar atomic absorption that we ascribe to the presence of a large star-spot .
This spot is centred at a latitude of \sim 82 ^ { \circ } and covers approximately 4 per cent of the total surface area of the secondary .
In keeping with the high latitude spots mapped on the cataclysmic variables AE Aqr and BV Cen , the spot on RU Peg also appears slightly shifted towards the trailing hemisphere of the star .
Finally , we speculate that early mapping attempts which indicated non-symmetric irradiation patterns which extended beyond the terminator of CV donors could possibly be explained by a superposition of symmetric heating and a large spot .