1997/01/26 by David Tytler, Tytler, David
Physics and Astronomy · #Adaptive optics and wavefront sensing #Astronomy and Astrophysical Research #Astrophysics (astro-ph) #FOS: Physical sciences #History and Developments in Astronomy #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/9701197
9 pages, Talk at ESO Workshop April 1st 1996, to appear in: Science with the VLTI (1997) ed. F. Paresce, (Springer: Heidelberg)
arxiv created 1997/01/26 · openalex publication_date 1997/01/26 · arxiv updated 2009/12/01 · openalex created_date 2025/10/24 · openalex updated_date 2026/07/28
Cosmology with large interferometric telescopes is a rich and largely\nunexplored subject, involving three types of measurement: astrometric\nmeasurement of absolute distances and proper motions, dispersions of relative\nproper motions, and images. The ground based interferometers can have huge\napertures, which are necessary for faint cosmological targets. But, alone, they\nare limited to astrometry within the isoplanatic patch, and hence to relative\npositions, which are of little use for parallaxes and proper motions because\nreference stars have unknown parallaxes and huge (500 \μ arcsec) unknown\nmotions. We propose that space missions should measure global astrometric\nparallaxes and proper motions for (V > 16) reference stars within the\nisoplanatic patches of important cosmological and Galactic targets. Ground\nbased interferometers can then measure absolute distances (parallaxes) and\nproper motions to 10 \μ arcsec, tied to these reference stars. But\ncosmological observations stretch the VLTI technically. To observe the few best\ntargets, we need to be able to measure positions to < 10 \μ arcsec over a\nlarge portion of the sky. Since natural guide stars are too far apart, or too\nfaint, laser guide stars are needed to correct the wavefronts of the individual\n8-m unit telescopes, and the fringe tracking system must have an extremely high\nthroughput to work on the brightest stars (V > 16) near to important targets.\nMost of the science is at 1 --2 microns, where excellent adaptive optics will\nbe needed on the 8-m telescopes.\n