Nonradial oscillations of the β Cephei star 12 Lacertae

As a result of a frequency analysis of the published observations of 12 Lacertae, six short-period sine-wave components are found in the star's light variation. It is concluded that 12 Lacertae is a slowly rotating nonradial oscillator in which two spherical harmonic modes of different degree are simltaneously excited. If use is made of the line profile observations, the triplet frequencies can be identified as corresponding to 1 = 3, m = -1, -2, -3 oscillations, and the star is found to be seen more nearly pole-on than equator-on. Finally, a comparison is briefly made with two other multiperiodic β Cephei variables, NU Eridani and β Canis Majoris. A solution of the well-known discrepancies in the case of β Canis Majoris is suggested. (author)