ARlogo Annu. Rev. Astron. Astrophys. 2014. 54:
Copyright © 2014 by Annual Reviews. All rights reserved

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MICRO-ARCSECOND RADIO ASTROMETRY

M.J. Reid 1 & M. Honma 2


1 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, U.S.A.
2 Mizusawa VLBI Observatory, National Astronomical Observatory of Japan & Department of Astronomical Science, The Graduate University for Advanced Study, Mitaka 181-8588, Japan

Abstract: Astrometry provides the foundation for astrophysics. Accurate positions are required for the association of sources detected at different times or wavelengths, and distances are essential to estimate the size, luminosity, mass, and ages of most objects. Very Long Baseline Interferometry at radio wavelengths, with diffraction-limited imaging at sub-milliarcsec resolution, has long held the promise of micro-arcsecond astrometry. However, only in the past decade has this been routinely achieved. Currently, parallaxes for sources across the Milky Way are being measured with ~ 10 μas accuracy and proper motions of galaxies are being determined with accuracies of ~ 1 μas y-1. The astrophysical applications of these measurements cover many fields, including star formation, evolved stars, stellar and super-massive black holes, Galactic structure, the history and fate of the Local Group, the Hubble constant, and tests of general relativity. This review summarizes the methods used and the astrophysical applications of micro-arcsecond radio astrometry.


Key words: Distance, Parallax, Proper Motion, VLBI, Galactic Structure, Star Formation, Evolved Stars, Pulsars, Hubble Constant


Table of Contents

INTRODUCTION
History
Radio Astrometry

ASTROPHYSICAL APPLICATIONS
Galactic Structure
Star Formation
Asymptotic Giant Branch Stars
X-ray Binaries
Pulsars
Radio Stars
Star Clusters
Sgr A*
Megamasers and the Hubble Constant
Extragalactic Proper Motions
Tests of General Relativity
Extrasolar Planets and Brown Dwarfs
AGN Cores
Satellite Tracking

ARRAYS FOR RADIO ASTROMETRY

FUNDAMENTALS OF RADIO ASTROMETRY
Relative Astrometry
Sources of Delay Error
Observing methods

ADVANCED TECHNIQUES
Tropospheric Delay Calibration
Ionospheric Delay Calibration
Dual-beam Systems
Reference Source Position
Source Elevation Limits
Measuring Positions

FUTURE
Space VLBI
The Event Horizon Telescope
Square Kilometer Array

REFERENCES

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