Heimdallr and Solarstein: alignment, calibration, and correction in the Asgard suite at the VLTI

TL;DR

This paper introduces the Heimdallr beam combiner and Solarstein simulator for the Asgard suite at VLTI, demonstrating their design, implementation, and calibration techniques to enable advanced interferometric observations.

Contribution

It presents the design and verification of Heimdallr and Solarstein, facilitating alignment, calibration, and diffraction-limited beam combination for the Asgard instrument suite.

Findings

Heimdallr achieves diffraction-limited beam combination in K band.

Solarstein provides an interface for alignment and calibration similar to VLTI.

Techniques for aligning large bulk optics instruments are shared.

Abstract

The Asgard instrument suite proposed for the ESO's Very Large Telescope Interferometer (VLTI) brings with it a new generation of instruments for spectroscopy and nulling. Asgard will enable investigations such as measurement of direct stellar masses for Galactic archaeology and direct detection of giant exoplanets to probe formation models using the first nulling interferometer in the southern hemisphere. We present the design and implementation of the Astralis-built Heimdallr, the beam combiner for fringe tracking and stellar interferometry in K band, as well as Solarstein, a novel implementation of a 4-beam telescope simulator for alignment and calibration. In this update, we verify that the Heimdallr design is sufficient to perform diffraction-limited beam combination. Furthermore, we demonstrate that Solarstein presents an interface comparable to the VLTI with co-phased, equal intensity beams, enabling alignment and calibration for all Asgard instruments. In doing so, we share techniques for aligning and implementing large instruments in bulk optics.