The spectroscopic binary eta Andromedae: Determination of the orbit by optical interferometry

We have determined the following orbital elements of the double-lined spectroscopic binary η Andromedae (combined spectral class G8 IIIb) using measurements with the Mark III long baseline optical interferometer on Mt. Wilson: Period P=115.72±0.02d, major axis a=10.37±0.03 milliarcseconds, eccentricity e=0.006±0.002, epoch of periastron T=JD 2448013±2, inclination i=30.°5±0.°4, argument of ascending node Ω=69.°4±0.°6, and argument of periastron ω=215°±7°. The magnitude differences of the two components measured at λλ 800 nm, 550 nm, and 500 nm are 0. m 50±0. m 06, 0. m 55±0. m 08, and 0. m 56±0. m 09, respectively