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From sector 1--40 {em TESS} observations, 20 new roAp stars, 97 ostensibly non-peculiar stars with roAp-like frequencies (the roA variables) and 617 $delta$~Scuti stars with independent frequencies typical of roAp stars were found. There is no criterion that can distinguish roAp/roA stars from $delta$~Sct stars. For expediency, an arbitrary low frequency of 60,d$^{-1}$ was chosen as the boundary between the $delta$~Sct and roAp/roA classes. Because an unknown mode selection process is clearly present in $delta$~Sct stars, the roAp/roA stars may be considered as $delta$~Sct stars in which high frequencies are preferentially selected. This interpretation is supported by the fact that the combined proportion of $delta$~Sct and roAp stars among Ap stars is the same as among non-Ap stars. Contrary to models, observations show that low frequencies in Ap stars are not suppressed. One of the most puzzling aspects of roAp stars is the large fraction which have short mode lifetimes. The failure of current models to explain these results may be due to an incorrect treatment of the outer layers of these stars.
Chemical element transport processes are among the crucial physical processes needed for precise stellar modelling. Atomic diffusion by gravitational settling nowadays is usually taken into account, and is essential for helioseismic studies. On the o
We analyze the X-ray spectra of 19 main sequence stars observed by Chandra using its LETGS configuration. Emission measure (EM) distributions are computed based on emission line measurements, an analysis that also yields evaluations of coronal abunda
During the last two years we have received long time-series photometric observations of bright (V mag < 8) main-sequence A- and B-type stars observed by the NASA TESS spacecraft and the Austria-Poland-Canada BRITE satellites. Using TESS observations
The understanding of the rotational evolution of early-type stars is deeply related to that of anisotropic mass and angular momentum loss. In this paper, we aim to clarify the rotational evolution of rapidly rotating early-type stars along the main s
We study the effects of feebly or non-annihilating weakly interacting Dark Matter (DM) particles on stars that live in DM environments denser than that of our Sun. We find that the energy transport mechanism induced by DM particles can produce unusua