GRAVITY acquisition camera: characterization results

TL;DR

The paper presents the characterization and on-sky operational results of the GRAVITY acquisition camera, which performs multiple optical functions for beam tracking and stabilization in the VLTI system.

Contribution

It provides detailed characterization results and demonstrates successful on-sky operation of the GRAVITY acquisition camera with its data reduction software.

Findings

Successful on-sky closed-loop operation achieved

Effective beam stabilization parameters estimation

Enhanced alignment and stabilization of the VLTI system

Abstract

GRAVITY acquisition camera implements four optical functions to track multiple beams of Very Large Telescope Interferometer (VLTI): a) pupil tracker: a $2 \times 2$ lenslet images four pupil reference lasers mounted on the spiders of telescope secondary mirror; b) field tracker: images science object; c) pupil imager: reimages telescope pupil; d) aberration tracker: images a Shack-Hartmann. The estimation of beam stabilization parameters from the acquisition camera detector image is carried out, for every 0.7 s, with a dedicated data reduction software. The measured parameters are used in: a) alignment of GRAVITY with the VLTI; b) active pupil and field stabilization; c) defocus correction and engineering purposes. The instrument is now successfully operational on-sky in closed loop. The relevant data reduction and on-sky characterization results are reported.