We present optical spectroscopy and extensive RI differential photometry of the double-lined eclipsing binary NSVS 02502726 ( 2MASS J08441103+5423473 ) .
Simultaneous solution of two-band light curves and radial velocities permits determination of precise emprical masses and radii for both components of the system .
The analysis indicates that the primary and secondary components of NSVS 02502726 are in a circular orbit with 0.56-day orbital period and have stellar masses of M _ { 1 } =0.714 \pm 0.019 M _ { \odot } , and M _ { 2 } =0.347 \pm 0.012 M _ { \odot } .
Both of the components have large radii , being R _ { 1 } =0.645 \pm 0.006 R _ { \odot } , and R _ { 2 } =0.501 \pm 0.005 R _ { \odot } .
The principal parameters of the mass and radius of the component stars are found with an accuracy of 3 % and 1 % , respectively .
The secondary component ’ s radius is significantly larger than model predictions for its mass , similar to what is seen in almost all of the other well-studied low-mass stars which belong to double-lined eclipsing binaries .
Strong H _ { \alpha } emission cores and considerable distortion at out-of-eclipse light curve in both R and I bandpasses , presumably due to dark spots on both stars , have been taken as an evidence of strong stellar activity .
The distance to system was calculated as 173 \pm 8 pc from the BVRIJHK magnitudes .
The absolute parameters of the components indicate that both components are close to the zero-age main-sequence .
Comparison with current stellar evolution models gives an age of 126 \pm 30 Myr , indicating the stars are in the final stages of pre-main-sequence contraction .