Nature of non-pulsating stars in the Cepheid instability strip

Determine the physical nature of the non-pulsating giant stars located within the Cepheid instability strip in the Large Magellanic Cloud and establish the mechanism responsible for their lack of detectable pulsations.

Background

The paper investigates candidates that occupy the Cepheid instability strip in the Large Magellanic Cloud but do not exhibit detectable photometric variability. Their atmospheric parameters are found to be broadly consistent with those of classical Cepheids, so inaccurate temperatures, gravities, reddening corrections, or metallicities do not provide a satisfactory explanation.

The authors discuss several possible mechanisms, including unresolved binarity, non-radial pulsation modes with large spherical-harmonic degree, high-order radial strange modes, and evolutionary changes caused by past binary mass transfer. The study does not determine which mechanism, or combination of mechanisms, explains the phenomenon.

References

Although several scenarios have been proposed to explain this phenomenon, their nature remains unknown.

— Revisiting candidates for non-pulsating stars located in the Cepheid instability strip in the Large Magellanic Cloud  (2609.01011 - Narloch et al., 1 Sep 2026) in Abstract; Section 1, Introduction

The available data are also insufficient to verify the presence of high-order radial modes with large $n$ numbers.

— Revisiting candidates for non-pulsating stars located in the Cepheid instability strip in the Large Magellanic Cloud  (2609.01011 - Narloch et al., 1 Sep 2026) in Section 4, Results from the spectroscopy; Section 5, Summary and conclusions