Imaging the Algol Triple System in H Band with the CHARA Interferometer

TL;DR

This study uses high-resolution interferometry to image the hierarchical triple system Algol in the H band, providing detailed orbital parameters, improved mass estimates, and visual confirmation of Roche-lobe filling secondary star.

Contribution

First direct imaging of the Algol triple system with interferometry, revealing detailed orbital and stellar properties and improving previous measurements.

Findings

Resolved all three stars unambiguously.

Reconstructed 55 phases of the inner orbit.

Found the mutual orbit inclination to be nearly perpendicular.

Abstract

Algol (Beta Per) is an extensively studied hierarchical triple system whose inner pair is a prototype semi-detached binary with mass transfer occurring from the sub-giant secondary to the main-sequence primary. We present here the results of our Algol observations made between 2006 and 2010 at the CHARA interferometer with the Michigan Infrared Combiner in the H band. The use of four telescopes with long baselines allows us to achieve better than 0.5 mas resolution and to unambiguously resolve the three stars. The inner and outer orbital elements, as well as the angular sizes and mass ratios for the three components are determined independently from previous studies. We report a significantly improved orbit for the inner stellar pair with the consequence of a 15% change in the primary mass compared to previous studies. We also determine the mutual inclination of the orbits to be much closer to perpendicularity than previously established. State-of-the-art image reconstruction algorithms are used to image the full triple system. In particular an image sequence of 55 distinct phases of the inner pair orbit is reconstructed, clearly showing the Roche-lobe-filling secondary revolving around the primary, with several epochs corresponding to the primary and secondary eclipses.