Beam combiner for the Asgard/BIFROST instrument

TL;DR

BIFROST is a planned high-resolution, short-wavelength beam combiner for the VLT Interferometer, designed to enhance spatial and spectral observations with innovative beam combination schemes.

Contribution

This paper presents the design and comparison of two beam combination schemes for BIFROST, a new instrument for high-resolution interferometric observations.

Findings

Comparison of AIO and IO beam combination schemes

Analysis of sensitivity and implementation challenges

Design considerations for high spectral resolution observations

Abstract

BIFROST will be a short-wavelength ($\lambda$ = 1.0 - 1.7$\mu$m) beam combiner for the VLT Interferometer, combining both high spatial ($\lambda$/2B = 0.8 mas) and spectral (up to R = 25,000) resolution. It will be part of the Asgard Suite of visitor instruments. The new window of high spectral resolution, short wavelength observations brings with it new challenges. Here we outline the instrumental design of BIFROST, highlighting which beam combiner subsystems are required and why. This is followed by a comparison All-In-One (AIO) beam combination scheme and an Integrated Optics (IO) scheme with ABCD modulation both in terms of expected sensitivity and the practical implementation of each system.