Long Period Variables: questioning the pulsation paradigm

TL;DR

This paper questions the traditional pulsation paradigm for long period variables, proposing that a close companion may better explain their variability based on analysis of light curves and spectral features.

Contribution

It introduces an alternative hypothesis that a close companion, rather than pulsation, accounts for the observed variability of long period variables.

Findings

Light curve analysis supports companion hypothesis

Spectral features consistent with binary interactions

Challenges to pulsation theory are highlighted

Abstract

Long period variables, among them Miras, are thought to be pulsating. Under this approach the whole star inflates and deflates along a period that can vary from 100 to 900 days; that pulsation is assumed to produce shock waves on the outer layers of the star that propagate into the atmosphere and could account for the increase in luminosity and the presence of emission lines in the spectra of these stars. However, this paradigm can seriously be questioned from a theoretical point of view. First, in order to maintain a radial pulsation, the spherical symmetry of the star must be preserved: how can it be reconciled with the large convective cells present in these stars? or when close companions are detected? Secondly, how different radial and non-radial pulsation modes of a sphere could be all damped except one radial mode? These problems have no solution and significantly weigh on the pulsation paradigm. Acknowledging this inconsistency, we show that a close companion around these stars could account for the star variability. To support this assertion we study the observed light curves, their shapes at different wavelengths and their changes over time.