New multiband CCD photometry is presented for the eclipsing binary GW Gem ; the RI light curves are the first ever compiled .
Four new minimum timings have been determined .
Our analysis of eclipse timings observed during the past 79 years indicates a continuous period increase at a fractional rate of + ( 1.2 \pm 0.1 ) \times 10 ^ { -10 } , in excellent agreement with the value + 1.1 \times 10 ^ { -10 } calculated from the Wilson-Devinney binary code .
The new light curves display an inverse O ’ Connell effect increasing toward longer wavelengths .
Hot and cool spot models are developed to describe these variations but we prefer a cool spot on the secondary star .
Our light-curve synthesis reveals that GW Gem is in a semi-detached , but near-contact , configuration .
It appears to consist of a near-main-sequence primary star with a spectral type of about A7 and an evolved early K-type secondary star that completely fills its inner Roche lobe .
Mass transfer from the secondary to the primary component is responsible for the observed secular period change .