The Short Period Light and Velocity Variations in Alpha Virginis

Abstract

The light variation of α Virginis (Spica) has been followed over a total of 26 nights in 1968, 1969 and 1970. On seven nights in 1970, three-colour observations were made. Both the 4-day variation with the orbital period and the 4-hr variation due to Beta Canis Majoris type pulsation (already reported in a previous paper) were evident; the amplitude of the short period appears to be randomly variable suggesting that the mode of pulsation is unstable. New spectra have been obtained and the radial velocities discussed together with others published from 1890 to 1956. The 4-hr period is also found in part of this data but some of the earlier velocities indicate the presence of at least three more periodicities, including one of about 6 hr. It is suggested that the 4-hr period currently observed is only a first overtone pulsation and that the 6-hr period is the fundamental. The period of the 4-hr pulsation is variable although the form of the variation cannot be uniquely determined. The phase relationships between the light, colour and velocity variations during the 4-hr period are investigated and the temperature variation estimated. The phase relationships are the same as for other β CMa stars for which these parameters have been observed; that is, maximum light and temperature occur at, or very close to, minimum radius.