The Blazhko Effect in Delta Scuti and other Groups of Pulsating Stars

TL;DR

This paper explores the Blazhko Effect across various pulsating stars, revealing multiple causes such as mode beating and stellar cycles, with detailed analysis of delta Scuti stars and long-term frequency variations.

Contribution

It extends the concept of the Blazhko Effect to other pulsating stars and provides detailed observational evidence of multiple underlying mechanisms.

Findings

Beating explains short-term modulations in delta Scuti stars.

Long-term frequency variations suggest stellar cycle influences.

Differential rotation changes are linked to stellar cycles.

Abstract

Amplitude and period variations have been detected in almost all types of pulsating stars. Many of these modulations are nearly periodic. In RR Lyrae stars the phenomenon in known as the Blazhko Effect. Because of the observed similarities, we propose to extend the definition to other groups. We illustrate the Blazhko Effect with examples from Cepheids, RR Lyrae stars, White Dwarfs, sdB stars and delta Scuti variables. For delta Scuti stars the present results indicate the presence of at least two effects: beating of independent modes with close frequencies and stellar cycles. For period and amplitude changes with timescales less than one year, the beating hypothesis explains the observed modulations very well. This has been shown by the correctly correlated relationship between amplitude and phase changes as well as the repetitions of these cycles. However, the observed period variations with longer timescales cannot be due to simple beating between two close frequencies. For the star AI CVn (= 4 CVn), we can derive accurate annual frequency values for a number of radial and nonradial modes from 1974 to 2009. For prograde and retrograde modes, the frequency variations are of similar size, but with opposite signs. The radial mode shows no (or little) changes. Fur- thermore, all frequency variations show a reversal around 1990. These results are consistent with long-term cycles affecting individual modes differently with some common systematic behavior. The observed change in the size of rotational splitting is interpreted as a change in the differential rotation during the stellar cycle.