TESS observations of Be stars: A new interpretation

Abstract

Light curves of 57 classical Be stars in TESS sectors 1-15 are examined. In most Be stars, the periodogram shows groups at a fundamental and one or more harmonics, which we attribute to rotation. In about 40 per cent of the stars, the group is just a single narrow or slightly broadened peak. In about 30 per cent, it consists of a multiple, closely spaced peaks. These groups can be interpreted as non-coherent variations most likely associated with photospheric gas clouds. Approximate rotational frequencies for about 74 per cent of the stars can be derived. Comparison with the projected rotational velocities shows that the photometric frequency is consistent with rotation. The first harmonic plays a prominent role in many Be stars and manifests itself in either single-wave or double-wave light curves. The reduction in amplitude of β Cep pulsations in a few Be stars during an outburst and their subsequent recovery is most likely an obscuration effect. Other instances of possible obscuration of the photosphere are suspected. A simple model, which attempts to explain these observations and other general properties of Be stars, is proposed.