We present a detailed analysis of the detached eclipsing binary CD Tau .
A large variety of observational data , in form of IR photometry , CORAVEL radial velocity observations and high-resolution spectra , are combined with the published light curves to derive accurate absolute dimensions and effective temperature of the components , as well as the metal abundance of the system .
We obtain : M _ { A } = 1.442 ( 16 ) M _ { \odot } , R _ { A } = 1.798 ( 17 ) R _ { \odot } , { T _ { eff } } _ { A } = 6200 ( 50 ) K , M _ { B } = 1.368 ( 16 ) M _ { \odot } , R _ { B } = 1.584 ( 20 ) R _ { \odot } and { T _ { eff } } _ { B } = 6200 ( 50 ) K. The metal content of the system is determined to be [ Fe / H ] = +0.08 ( 15 ) dex .

In addition , the eclipsing binary has a K-type close visual companion at about 10-arcsec separation , which is shown to be physically linked , thus sharing a common origin .
The effective temperature of the visual companion ( { T _ { eff } } _ { C } = 5250 ( 200 ) K ) is determined from synthetic spectrum fitting , and its luminosity ( \log L / \mbox { L$ { } _ { \odot } $ } = -0.27 ( 6 ) ) , and therefore its radius ( R = 0.89 ( 9 ) R _ { \odot } ) , are obtained from comparison with the apparent magnitude of the eclipsing pair .

The observed fundamental properties of the eclipsing components are compared with the predictions of evolutionary models , and we obtain good agreement for an age of 2.6 Gyr and a chemical composition of Z = 0.026 and Y = 0.26 .
Furthermore , we test the evolutionary models for solar-mass stars and we conclude that the physical properties of the visual companion are very accurately described by the same isochrone that fits the more massive components .