Long Secondary Periods in Red Giants: AAVSO Observations and the Eclipse Hypothesis

TL;DR

This study investigates long secondary periods in red giants, supporting the eclipse hypothesis by analyzing long-term observations that reveal dust-enshrouded companions and amplitude variations without significant geometric changes.

Contribution

The paper provides observational evidence from AAVSO data supporting the eclipse hypothesis for LSPs and examines long-term amplitude and geometric stability in red giants.

Findings

Large LSP amplitudes linked to dust tails on companions

LSP amplitudes vary by up to a factor of 8 over decades

No significant change in system geometry over long timescales

Abstract

At least a third of red giants show a long secondary period (LSP), 5 to 10 times longer than the pulsation period. There is strong evidence that the LSP is caused by eclipses of the red giant by a dust-enshrouded low-mass companion. We have used long-term AAVSO observations of 11 stars to study two aspects of the eclipse hypothesis: the relation between the LSP phase (eclipse) curve and the geometry of the eclipse, and the long-term (decades) changes in the LSP phenomenon in each star. The stars with the largest LSP amplitudes show evidence of a dust tail on the companion, but most of the 11 stars show only a small-amplitude sinusoidal phase curve. The LSP amplitudes of all the stars vary slowly by up to a factor of 8, suggesting that the amount of obscuring dust varies by that amount, but there is no strong evidence that the geometry of the system changes over many decades.