  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: MA=1.442(16) Mo, RA=1.798(17) Ro, TeffA=6200(50) K, MB=1.368(16) Msun,
RB=1.584(20) Run and TeffB=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 (Teff=5250(200) K) is determined from synthetic
spectrum fitting, and its luminosity (log L/Lo=-0.27(6)), and therefore its
radius (R=0.89(9) Ro), 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.
