Interferometric Observations of the Hierarchical Triple System Algol

TL;DR

This study uses advanced interferometric techniques to determine the orbital orientation of the Algol triple system, revealing a mutual inclination of about 95 degrees and large long-term inclination variations consistent with observed photometric changes.

Contribution

It provides the first precise measurement of the mutual orbital inclination in Algol using optical/IR interferometry and numerical dynamics, clarifying previous uncertainties.

Findings

Mutual inclination of the close and wide pairs is approximately 95 degrees.

The orbital plane of the close pair shows large inclination variations over 20,000 years.

The measured orbital parameters align with observed photometric amplitude changes.

Abstract

Algol is a triple stellar system consisting of a close semidetached binary orbited by a third object. Due to the disputed spatial orientation of the close pair, the third body perturbation of this pair is a subject of much research. In this study, we determine the spatial orientation of the close pair orbital plane using the CHARA Array, a six-element optical/IR interferometer located on Mount Wilson, and state-of-the-art e-EVN interferometric techniques. We find that the longitude of the line of nodes for the close pair is $\Omega_1=48\degr\pm2\degr$ and the mutual inclination of the orbital planes of the close and the wide pairs is $95\degr\pm3\degr$. This latter value differs by $5\degr$ from the formerly known $100\degr$ which would imply a very fast inclination variation of the system, not borne out by the photometric observations. We also investigated the dynamics of the system with numerical integration of the equations of motions using our result as an initial condition. We found large variations in the inclination of the close pair (its amplitude $\sim 170\degr$) with a period of about 20 millennia. This result is in good agreement with the photometrically observed change of amplitude in Algol's primary minimum.