AMBER closure and differential phases: accuracy and calibration with a Beam Commutation

TL;DR

This paper evaluates the accuracy of differential and closure phase measurements with the AMBER instrument at VLTI, demonstrating that Beam Commutation calibration significantly improves measurement precision by reducing instrumental biases.

Contribution

It introduces and assesses a calibration technique called Beam Commutation that enhances the accuracy of phase measurements in astrophysical observations.

Findings

Beam Commutation improves phase measurement accuracy

Instrumental biases can be substantially mitigated

Calibration technique enhances astrophysical data quality

Abstract

The first astrophysical results of the VLTI focal instrument AMBER have shown the importance of the differential and closure phase measures, which are supposed to be much less sensitive to atmospheric and instrumental biases than the absolute visibility. However there are artifacts limiting the accuracy of these measures which can be substantially overcome by a specific calibration technique called Beam Commutation. This paper reports the observed accuracies on AMBER/VLTI phases in different modes, discusses some of the instrumental biases and shows the accuracy gain provided by Beam Commutation on the Differential Phase as well as on the Closure Phase.