Mobile Intensity Interferometer for Stellar Observations (MI$^2$SO)

TL;DR

This paper presents a novel, portable intensity interferometer using Fresnel lenses for stellar observations, successfully measuring the angular diameter of Arcturus with high precision in a short observation time.

Contribution

It introduces a lightweight, scalable, and mobile intensity interferometer design tailored for stellar measurements, demonstrating its effectiveness through a successful observation campaign.

Findings

Measured Arcturus's angular diameter with milliarcsecond accuracy

Demonstrated the interferometer's capability with less than 11 hours of observation

Validated the design's potential for targeted stellar observations

Abstract

In recent years, intensity interferometry has seen renewed interest and successful application at Imaging Atmospheric Cherenkov Telescope arrays. These measurements are usually performed during bright moon periods while the instruments' primary purpose -- gamma-ray observations -- cannot be fulfilled. The Mobile Intensity Interferometer for Stellar Observations was designed as a proof of concept for a purpose-built intensity interferometer. Using acrylic Fresnel lenses 1 m in diameter with 1.2 m focal length, a compact, economical and lightweight design was realised. The detector fixture allows for translation in the z-axis to adjust for measurements at different wavelengths (and therefore focal points) and easy swapping of the detector in its entirety. Both mobility and scalability in quantity of this design allow for specific targeting of projected baselines and orientations based on the target. Particularly for potential binary systems, selective coverage of a target's u-v plane is essential to probing the characteristics accurately. A first campaign demonstrated the capability of these Fresnel lens telescopes by measuring the spatial coherence curve of Arcturus ($\alpha$ Boo). In an observation time of less than 11 h, the angular diameter was measured with milliarcsecond precision, in agreement with the values in the literature.