Polarization analysis of the VLTI and GRAVITY
Abstract
The goal of this work is to characterize the polarization effects of the VLTI and GRAVITY. This is needed to calibrate polarimetric observations with GRAVITY for instrumental effects and to understand the systematic error introduced to the astrometry due to birefringence when observing targets with a significant intrinsic polarization. By combining a model of the VLTI light path and its mirrors and dedicated experimental data, we construct a full polarization model of the VLTI UTs and the GRAVITY instrument. We first characterize all telescopes together to construct a UT calibration model for polarized targets. We then expand the model to include the differential birefringence. With this, we can constrain the systematic errors for highly polarized targets. Together with this paper, we publish a standalone Python package to calibrate the instrumental effects on polarimetric observations. This enables the community to use GRAVITY to observe targets in a polarimetric observing mode. We demonstrate the calibration model with the galactic center star IRS 16C. For this source, we can constrain the polarization degree to within 0.4 % and the polarization angle within 5 deg while being consistent with the literature. Furthermore, we show that there is no significant contrast loss, even if the science and fringe-tracker targets have significantly different polarization, and we determine that the phase error in such an observation is smaller than 1 deg, corresponding to an astrometric error of 10 {\mu}as. With this work, we enable the use of the polarimetric mode with GRAVITY/UTs and outline the steps necessary to observe and calibrate polarized targets. We demonstrate that it is possible to measure the intrinsic polarization of astrophysical sources with high precision and that polarization effects do not limit astrometric observations of polarized targets.
Keywords
Cite
@article{arxiv.2311.03472,
title = {Polarization analysis of the VLTI and GRAVITY},
author = {GRAVITY Collaboration and F. Widmann and X. Haubois N. Schuhler and O. Pfuhl and F. Eisenhauer and S. Gillessen and N. Aimar and A. Amorim and M. Bauböck and J. B. Berger and H. Bonnet and G. Bourdarot and W. Brandner and Y. Clénet and R. Davies and P. T. de Zeeuw and J. Dexter and A. Drescher and A. Eckart and H. Feuchtgruber and N. M. Förster Schreiber and P. Garcia and E. Gendron and R. Genzel and M. Hartl and F. Haußmann and G. Heißel and T. Henning and S. Hippler and M. Horrobin and A. Jiménez-Rosales and L. Jocou and A. Kaufer and P. Kervella and S. Lacour and V. Lapeyrère and J. -B. Le Bouquin and P. Léna and D. Lutz and F. Mang and N. More and M. Nowak and T. Ott and T. Paumard and K. Perraut and G. Perrin and S. Rabien and D. Ribeiro and M. Sadun Bordoni and S. Scheithauer and J. Shangguan and T. Shimizu and J. Stadler and O. Straub and C. Straubmeier and E. Sturm and L. J. Tacconi and F. Vincent and S. D. von Fellenberg and E. Wieprecht and E. Wiezorrek and J. Woillez},
journal= {arXiv preprint arXiv:2311.03472},
year = {2023}
}
Comments
Accepted by A&A