Interferometric Observations of Algol

TL;DR

This study used optical and radio interferometry to determine the orbital orientation of the Algol system, revealing a mutual inclination that challenges previous assumptions and indicating long-term dynamical variations consistent with observed photometric changes.

Contribution

The paper provides the first combined optical and radio interferometric measurement of Algol's orbital planes and models its long-term dynamical evolution.

Findings

Mutual inclination of 95° between orbital planes

Large inclination variations (~170°) over 20,000 years

Agreement with observed changes in Algol's primary minimum

Abstract

We determined the spatial orientation of the Algol AB close pair orbital plane using optical interferometry with the CHARA Array, and radio interferometry with the European VLBI Network (EVN). We found the longitude of the line of nodes for the close pair being $\Omega_1=48\deg\pm2\deg$ and the mutual inclination of the orbital planes of the close and the wide pairs being $95\deg\pm3\deg$. This latter value differs by $5\deg$ from the formerly known $100\deg$ which would imply a very fast inclination variation of the system, not supported 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 $\sim 170\deg$) with a period of about 20 millenia. This result is in good agreement with the photometrically observed change of amplitude in Algol's primary minimum.