We report extensive spectroscopic and differential photometric BV RI observations of the active , detached , 1.309-day double-lined eclipsing binary IM Vir , composed of a G7-type primary and a K7 secondary .
With these observations we derive accurate absolute masses and radii of M _ { 1 } = 0.981 \pm 0.012 ~ { } M _ { \sun } , M _ { 2 } = 0.6644 \pm 0.0048 ~ { } M _ { \sun } , R _ { 1 } = 1.061 \pm 0.016 ~ { } R _ { \sun } , and R _ { 2 } = 0.681 \pm 0.013 ~ { } R _ { \sun } for the primary and secondary , with relative errors under 2 % .
The effective temperatures are 5570 \pm 100 K and 4250 \pm 130 K. The significant difference in mass makes this a favorable case for comparison with stellar evolution theory .
We find that both stars are larger than the models predict , by 3.7 % for the primary and 7.5 % for the secondary , as well as cooler than expected , by 100 K and 150 K , respectively .
These discrepancies are in line with previously reported differences in low-mass stars , and are believed to be caused by chromospheric activity , which is not accounted for in current models .
The effect is not confined to low-mass stars : the rapidly-rotating primary of IM Vir joins the growing list of objects of near-solar mass ( but still with convective envelopes ) that show similar anomalies .
The comparison with the models suggests an age of 2.4 Gyr for the system , and a metallicity of [ Fe/H ] \approx - 0.3 that is consistent with other indications , but requires confirmation .