Pulsation among TESS A and B stars and the Maia variables

Abstract

Classification of over 50 000 TESS stars in sectors 1–18 has resulted in the detection of 766 pulsating main-sequence B stars as well as over 5000 δ Scuti, 2300 γ Doradus, and 114 roAp candidates. Whereas it has been assumed that high-frequency pulsations among B-type main-sequence stars are confined to the early B-type β Cephei stars, the observations indicate that high frequencies are to be found over the whole B-star range, eventually merging with δ Scuti stars. The cool B stars pulsating in high frequencies are called Maia variables. It is shown that Maia variables are not rapidly rotating and thus cannot be β Cephei pulsators that appear to have lower temperatures due to gravity darkening. In the region where β Cephei variables are found, the proportion of pulsating stars is larger and amplitudes are higher and a considerable fraction pulsate in a single mode and low rotation rate. There is no distinct region of slowly pulsating B stars (SPB stars). Stars pulsating solely in low frequencies are found among all B stars. At most, only one-third of B stars appear to pulsate. These results, as well as the fact that a large fraction of A and B stars show rotational modulation, indicate a need for a revision of current ideas regarding stars with radiative envelopes.