Chromospherically Active Stars. XVI. The Double-Lined Binary 42 Capricorni

New spectroscopic observations of the chromospherically active binary, 42 Capricorni, have resulted in the detection of lines of the secondary, improved orbital elements, and the determination of fundamental properties of the components. 42 Cap has an orbital period of 13.174004 d, an eccentricity of 0.176, and a mass ratio A/B of 1.375. No evidence for a variation of the center-of-mass velocity, suggested by earlier investigators, has been found. Spectral types of the primary and secondary are G1 IV and G2 V, respectively. The V mag difference of 1.94 and HIPPARCOS parallax result in M_V = 2.79 mag for A and M_V = 4.73 for B. The spectral type of the secondary implies a mass of 1.37 M_sun for the primary and an orbital inclination of 30°. The primary has begun its evolution through the Hertzsprung Gap and has a radius of 2.6 R_sun. Comparison with evolutionary tracks results in an age of about 3.7 Gyr for the system. The subgiant has a log lithium abundance of 2.36, indicating that it is not a lithium-dip star.