Stochastic Processes in Yellow and Red Pulsating Variables

TL;DR

This paper investigates stochastic variations in pulsation periods of various pulsating stars, analyzing their nature, correlation with stellar properties, and potential physical origins.

Contribution

It provides a comprehensive analysis of random pulsation period changes across different types of pulsating stars and explores their possible physical mechanisms.

Findings

Stochastic period changes are common in cool pulsating stars.

The randomness parameter 'e' correlates with stellar radius and period.

Average e/P ratio is approximately 0.0136.

Abstract

Random changes in pulsation period are well established in cool pulsating stars, in particular the red giant variables: Miras, semi-regulars of types A and B, and RV Tau variables. Such effects are also observed in a handful of Cepheids, the SX Phe variable XX Cyg, and, most recently, the red supergiant variable, BC Cyg, a type C semi-regular. The nature of such fluctuations is seemingly random over a few pulsation cycles of the stars, yet the regularity of the primary pulsation mechanism dominates over the long term. The degree of stochasticity is linked to the dimensions of the stars, the randomness parameter 'e' appearing to correlate closely with mean stellar radius through the period 'P', with an average value of e/P = 0.0136+-0.0005. The physical processes responsible for such fluctuations are uncertain, but presumably originate in temporal modifications of envelope convection in such stars.