NEW PRECISION ORBITS OF BRIGHT DOUBLE-LINED SPECTROSCOPIC BINARIES. VIII. HR 1528, HR 6993, 2 SAGITTAE, AND 18 VULPECULAE

Improved orbital elements for four A-star double-lined spectroscopic binaries have been determined with numerous new radial velocities. Three of the four systems, HR 1528, 2 Sge, and 18 Vul, have moderately short orbital periods of 7.05, 7.39, and 9.31 days, respectively, and also have circular or nearly circular orbits. Only HR 6993 with a period of 14.68 days has a significantly eccentric orbit. The close visual companion of 2 Sge has been detected spectroscopically, and its velocity measured. The orbital dimensions (a(1) sin i and a(2) sin i) and minimum masses (m(1) sin(3) i and m(2) sin(3) i) of the short-period binary components all have accuracies of 0.5% or better. We determine basic properties of the individual stars and compare them with solar-abundance evolutionary tracks to estimate their masses. Half of the eight components may be synchronously or pseudosynchronously rotating.