On the sensitivity of closure phases to faint companions in optical long baseline interferometry

TL;DR

This paper analyzes how closure phases in optical long baseline interferometry can detect faint companions around bright stars, deriving a linear model and estimating detection efficiency for current telescope configurations.

Contribution

It introduces a linear expression for closure phase signatures of faint companions and evaluates detection efficiency across different interferometric array configurations.

Findings

All configurations detect companions wider than 10mas with similar efficiency.

Median dynamic range of up to six magnitudes with five observations at different hour angles.

Surveying bright stars for faint companions is an efficient filler program for interferometers.

Abstract

We explore the sensitivity and completeness of long baseline interferometric observations for detecting unknown, faint companions around bright unresolved stars. We derive a linear expression for the closure phase signature of a faint companion in the high contrast regime (<0.1), and provide a quantitative estimation of the detection efficiency for the currently offered four-telescope configurations at the Very Large Telescope Interferometer. The results are compared to the performances provided by linear and Y-shaped interferometric configurations in order to identify the ideal array. We find that all configurations have a similar efficiency in discovering companions wider than 10mas. Assuming a closure phase accuracy of 0.25deg, that is typical of state-of-the-art instruments, we predict a median dynamic range of up to six magnitudes when stacking observations obtained at five different hour angles. Surveying bright stars to search for faint companions can be considered as an ideal filler programme for modern interferometric facilities because that places few constraints on the choice of the interferometric configuration.