Taking the Measure of the Universe: Precision Astrometry with SIM Planetquest (Preprint).

摘要

Precision astrometry at microarcsecond accuracy has application to a wide range of astrophysical problems. This paper is a study of the science questions that can be addressed using an instrument with flexible scheduling that delivers parallaxes at about 4 microarcsecond on targets as faint as V = 20, and differential accuracy of 0.6 microarchsecond on bright targets. The science topics are drawn primarily from the Team Key Projects, selected in 2000, for the Space Interferometry Mission PlanetQuest (SIM PlanetQuest). We use the capabilities of this mission to illustrate the importance of the next level of astrometric precision in modern astrophysics. SIM PlanetQuest is currently in the detailed design phase. It will be the first space-based long baseline Michelson interferometer designed for precision astrometry. Using differential astrometry SIM will search for planets with masses as small as an Earth orbiting in the 'habitable zone' around the nearest stars. It will characterize the multiple-planet systems known to exist, and it will be able to search for terrestrial planets around candidate target stars in the Terrestrial Planet Finder and Darwin mission lists. It will be capable of detecting planets around young stars, thereby providing insights into how planetary systems are born and how they evolve. Precision astrometry allows the measurement of accurate dynamical masses for stars in binary systems. SIM will observe significant numbers of very high- and low-mass stars, providing stellar masses to 1%. Using precision proper motion measurements, SIM will probe the Galactic mass distribution, and through studies of tidal tails, the formation and evolution of the Galactic halo. SIM will contribute to cosmology through improved accuracy of the Hubble Constant. With repeated astrometric measurements of the nuclei of active galaxies, SIM will probe the dynamics of accretion disks around supermassive black holes, and the relativistic jets that emerge from them.