On the Six-year Period in the Radial Velocity of Antares A

We examine the century-long historical data and compare it with our new radial-velocity measurements to determine an improved period. We find a period of 2167 ± 5 days (5.93 ± 0.01 years). Both orbital motion and pulsation are considered as possible causes of the velocity variation. Temperature variations we deduce from line-depth ratios support the pulsation hypothesis. A temperature minimum occurs in 2009, 70 days after the radial-velocity minimum. We deduce a radius change of 19% ± 4% from an integration of the radial-velocity curve and predict a visual magnitude variation ~0.2 from the radius and temperature variation.