Rapidly-oscillating {\it TESS} A--F main sequence stars: are the roAp stars a distinct class?

TL;DR

This study analyzes TESS data to investigate whether rapidly oscillating Ap (roAp) stars are a distinct class, finding that they are indistinguishable from normal delta Scuti stars in frequency and pulsation characteristics.

Contribution

The paper provides a comprehensive analysis of TESS data, showing that roAp stars are not a separate class but are similar to normal delta Scuti stars, challenging previous classifications.

Findings

No distinct frequency separation between roAp and delta Scuti stars.

Chemically peculiar stars are more likely to pulsate at high frequencies.

The term 'roAp' should be discontinued as these stars are normal delta Scuti stars.

Abstract

From sector 1--44 {\em TESS} observations, 19 new roAp stars, 103 ostensibly non-peculiar stars with roAp-like frequencies and 617 $\delta$~Scuti stars with independent frequencies typical of roAp stars were found. Examination of all chemically peculiar stars observed by {\em TESS} resulted in the discovery of 199 Ap stars which pulsate as $\delta$~Sct or $\gamma$~Dor variables. The fraction of pulsating Ap stars is the same as the fraction of pulsating chemically normal stars. There is no distinct separation in frequency or radial order between chemically peculiar $\delta$~Sct stars and roAp stars. In fact, all the features which originally distinguished roAp from $\delta$~Sct stars in the past have disappeared. There is no reason to assume that the high frequencies in roAp stars are driven by a different mechanism from the high frequencies in chemically normal stars. However, chemically peculiar stars are far more likely to pulsate with high frequencies. The term "roAp" should be dropped: all roAp stars are normal $\delta$~Scuti stars.