The GRAVITY fringe tracker: correlation between optical path residuals and atmospheric parameters

TL;DR

This study analyzes the relationship between optical path residuals and atmospheric conditions in the GRAVITY fringe tracker, revealing key correlations that impact fringe tracking performance.

Contribution

It provides the first detailed correlation analysis between optical path residuals and atmospheric parameters for the GRAVITY fringe tracker.

Findings

Median residuals are 180 nm on ATs and 270 nm on UTs.

Residuals are uncorrelated with target magnitudes below Kmag 5.5 (ATs) and 9 (UTs).

Fringe tracking performance drops significantly below 3 ms coherence time.

Abstract

After the first year of observations with the GRAVITY fringe tracker, we compute correlations between the optical path residuals and atmospheric and astronomical parameters. The median residuals of the optical path residuals are 180 nm on the ATs and 270 nm on the UTs. The residuals are uncorrelated with the target magnitudes for Kmag below 5.5 on ATs (9 on UTs). The correlation with the coherence time is however extremely clear, with a drop-off in fringe tracking performance below 3 ms.