The hot Gamma-Doradus and Maia stars

TL;DR

This paper investigates anomalous pulsating stars, the hot Gamma-Doradus and Maia types, which exhibit unusual pulsation patterns and locations in the Hertzsprung-Russell diagram, challenging current stellar models.

Contribution

It provides spectroscopic data and analysis that support the existence of these anomalous pulsators, highlighting gaps in current stellar pulsation theories.

Findings

Hot Gamma-Doradus stars show low frequencies but are stable in models.

Maia candidates exhibit high frequencies but are located outside known instability strips.

Spectroscopic analysis confirms these stars are anomalous pulsators.

Abstract

The hot $\gamma$~Doradus stars have multiple low frequencies characteristic of $\gamma$~Dor or SPB variables, but are located between the red edge of the SPB and the blue edge of the $\gamma$~Dor instability strips where all low-frequency modes are stable in current models of these stars. Though $\delta$~Sct stars also have low frequencies, there is no sign of high frequencies in hot $\gamma$~Dor stars. We obtained spectra to refine the locations of some of these stars in the H-R diagram and conclude that these are, indeed, anomalous pulsating stars. The Maia variables have multiple high frequencies characteristic of $\beta$~Cep and $\delta$~Sct stars, but lie between the red edge of the $\beta$~Cep and the blue edge of the $\delta$~Sct instability strips. We compile a list of all Maia candidates and obtain spectra of two of these stars. Again, it seems likely that these are anomalous pulsating stars which are currently not understood.