EL CMi: confirmation of triaxial pulsation theory

TL;DR

This paper reports the first detection of a quadrupole Tidally Tilted Standing mode in a close binary star system, demonstrating the potential of asteroseismology to study stellar structure in such systems.

Contribution

It provides the first observational evidence of TTS modes in a binary star, confirming theoretical predictions and combining multiple observational techniques for comprehensive analysis.

Findings

Detection of quadrupole TTS oscillation mode in EL CMi

Presence of two dipole oscillations in the system

Characterization of the binary's stellar components and evolution

Abstract

Triaxial pulsators are a recently discovered group of oscillating stars in close binary systems that show pulsations around three axes at the same time. It has recently been theoretically shown that new types of pulsation modes, the Tidally Tilted Standing (TTS) modes, can arise in such stars. Here, we report the first detection of a quadrupole TTS oscillation mode in the pulsating component of the binary system EL CMi following an analysis of TESS space photometry. Two dipole oscillations around different axes in the orbital plane are present as well. In addition, the binary system is characterized using new radial velocity measurements, phoebe as well as simultaneous spectral energy distribution and light curve modeling. The pulsating primary component has properties typical of a Delta Scuti star but has accreted and is still accreting mass from its Roche Lobe filling companion. The donor star is predicted to evolve into a low-mass helium white dwarf. EL CMi demonstrates the potential of asteroseismic inferences of the structure of stars in close binaries before and after mass transfer and in three spatial dimensions.