TESS observations of Be stars: a new interpretation

TL;DR

This study analyzes TESS light curves of 57 Be stars, revealing rotation-related variability, non-coherent gas cloud signatures, and pulsation behavior, leading to a new interpretation of Be star phenomena.

Contribution

It introduces a new model explaining Be star variability, emphasizing the role of photospheric gas clouds and rotation, based on extensive TESS observations.

Findings

Most Be stars show rotation-related frequency groups in light curves.

Photometric frequencies align with rotational velocities from spectroscopic data.

Obscuration effects influence pulsation amplitudes during outbursts.

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 percent of the stars, the group is just a single narrow or slightly broadened peak. In about 30 percent, 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 75 percent 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 beta 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.