Amplitude Variations in Pulsating Red Giants. II. Some Systematics

TL;DR

This study analyzes long-term observations of pulsating red giants to investigate their cyclic amplitude variations, revealing consistent patterns across different star types but leaving the cause of these variations unexplained.

Contribution

It extends previous research by analyzing a larger sample of red giants using AAVSO data and identifies systematic properties of amplitude variations.

Findings

Amplitude variation factor around 1.5

Variation time scale of 20-35 pulsation periods

Similar variation patterns across different star types

Abstract

In order to extend our previous studies of the unexplained phenomenon of cyclic amplitude variations in pulsating red giants, we have used the AAVSO time-series analysis package VSTAR to analyze long-term AAVSO visual observations of 50 such stars, mostly Mira stars. The relative amount of the variation, typically a factor of 1.5, and the time scale of the variation, typically 20-35 pulsation periods, are not significantly different in longer-period, shorter-period, and carbon stars in our sample, and they also occur in stars whose period is changing secularly, perhaps due to a thermal pulse. The time scale of the variations is similar to that in smaller-amplitude SR variables, but the relative amount of the variation appears to be larger in smaller-amplitude stars, and is therefore more conspicuous. The cause of the amplitude variations remains unknown.