The radius and the pulsation constant of the primary of Spica

Abstract

In the late sixties, Spica (α Virginia, a 4.01454-day SB2 and interferometric binary, with a B1 IV primary component) was showing a light variation that consisted of two periodic terms. One term had the form of a double wave with the above-mentioned orbital period, the other was sinusoidal in shape and had a period equal to 0.1738 days. The double-wave term was clearly an ellipsoidal variation, caused by aspect changes of the tidally distorted primary, whereas the short-period term could only be explained as due to the primary's β Cephei-type pulsations. However, in 1972 these pulsations became undetectable.