{"paper":{"title":"The GRAVITY metrology system: narrow-angle astrometry via phase-shifting interferometry","license":"http://arxiv.org/licenses/nonexclusive-distrib/1.0/","headline":"","cross_cats":[],"primary_cat":"astro-ph.IM","authors_text":"A. Amorim, A. Janssen, A. Pfl\\\"uger, C. Straubmeier, D. Huber, E. Sturm, E. Wieprecht, F. Eisenhauer, F. Hau{\\ss}mann, G. Perrin, J. Weber, K. Perraut, L. Burtscher, M. Haug, M. Lippa, M. Sch\\\"oller, N. Blind, O. Hans, O. Pfuhl, R. Genzel, R. Gre{\\ss}mann, R. Hofmann, S. Gillessen, S. Huber, S. Kellner, S. Senftleben, T. Ott, W. Brandner, Y. Kok","submitted_at":"2015-01-20T08:54:10Z","abstract_excerpt":"The VLTI instrument GRAVITY will provide very powerful astrometry by combining the light from four telescopes for two objects simultaneously. It will measure the angular separation between the two astronomical objects to a precision of 10 microarcseconds. This corresponds to a differential optical path difference (dOPD) between the targets of few nanometers and the paths within the interferometer have to be maintained stable to that level. For this purpose, the novel metrology system of GRAVITY will monitor the internal dOPDs by means of phase-shifting interferometry. We present the four-step "},"claims":{"count":0,"items":[],"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"source":{"id":"1501.04738","kind":"arxiv","version":1},"verdict":{"id":null,"model_set":{},"created_at":null,"strongest_claim":"","one_line_summary":"","pipeline_version":null,"weakest_assumption":"","pith_extraction_headline":""},"references":{"count":0,"sample":[],"resolved_work":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57","internal_anchors":0},"formal_canon":{"evidence_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"author_claims":{"count":0,"strong_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"builder_version":"pith-number-builder-2026-05-17-v1"}