LONG-PERIOD VARIATIONS IN THE RADIAL VELOCITY OF SPECTROSCOPIC BINARY M GIANT URSAE MAJORIS

ABSTRACT We report that the spectroscopic binary Ursae Majoris ( UMa) has secondary RV variations of 471.2 days in addition to those of 230.0 days already known. Keplerian orbit analysis yields stellar mass companions of 1.6 M for the 230 day period and 0.14 M for the 471 day period. However, the HIPPARCOS photometries show a period similar to the stellar rotational period, which is one-quarter of the RV period. Variations in the bisector velocity curvature show a period of 463.6 days. We also find ∼473 day variations in the equivalent width (EW) measurements of the and lines, whose origin is probably stellar activity. We note that the nature of 471 day variations is similar to one observed in "Sequence D" of Asymptotic Giant Branch pulsating stars. We therefore conclude that the RV and the EW variations in the spectroscopic binary M giant UMa A originate from the complex pulsations and the chromospheric activity.