( catalog Parenago 1802 ) , a member of the \sim 1 Myr Orion Nebula Cluster , is a double-lined , detached eclipsing binary in a 4.674 d orbit , with equal-mass components ( M _ { 2 } / M _ { 1 } =0.985 \pm 0.029 ) .
Here we present extensive VI _ { C } JHK _ { S } light curves spanning \sim 15 yr , as well as a Keck/HIRES optical spectrum .
The light curves evince a third light source that is variable with a period of 0.73 d , and is also manifested in the high-resolution spectrum , strongly indicating the presence of a third star in the system , probably a rapidly rotating classical T Tauri star .
We incorporate this third light into our radial velocity and light curve modeling of the eclipsing pair , measuring accurate masses ( M _ { 1 } =0.391 \pm 0.032 , M _ { 2 } =0.385 \pm 0.032 M _ { \sun } ) , radii ( R _ { 1 } =1.73 \pm 0.02 , R _ { 2 } =1.62 \pm 0.02 R _ { \sun } ) , and temperature ratio ( T _ { eff, 1 } / T _ { eff, 2 } =1.0924 \pm 0.0017 ) .
Thus the radii of the eclipsing stars differ by 6.9 \pm 0.8 % , the temperatures differ by 9.2 \pm 0.2 % , and consequently the luminosities differ by 62 \pm 3 % , despite having masses equal to within 3 % .
This could be indicative of an age difference of \sim 3 \times 10 ^ { 5 } yr between the two eclipsing stars , perhaps a vestige of the binary formation history .
We find that the eclipsing pair is in an orbit that has not yet fully circularized , e =0.0166 \pm 0.003 .
In addition , we measure the rotation rate of the eclipsing stars to be 4.629 \pm 0.006 d ; they rotate slightly faster than their 4.674 d orbit .
The non-zero eccentricity and super-synchronous rotation suggest that the eclipsing pair should be tidally interacting , so we calculate the tidal history of the system according to different tidal evolution theories .
We find that tidal heating effects can explain the observed luminosity difference of the eclipsing pair , providing an alternative to the previously suggested age difference .