HST FGS astrometry - the value of fractional millisecond of arc precision

TL;DR

This paper highlights the continued value of HST FGS astrometry for high-precision optical measurements, especially for galactic Cepheids and exoplanet host stars, before newer missions take over.

Contribution

It demonstrates the unique capabilities of HST FGS astrometry in achieving sub-milliarcsecond precision and its applications in astrophysics.

Findings

Precise parallaxes of galactic Cepheids obtained.

Determination of exoplanet companion masses through orbital perturbations.

HST FGS remains a valuable resource for high-precision astrometry.

Abstract

In a few years astrometry with the venerable combination of Hubble Space Telescope and Fine Guidance Sensor will be replaced by SIM, GAIA, and long-baseline interferometry. Until then we remain a resource of choice for sub-millisecond of arc precision optical astrometry. As examples we discuss 1) the uses which can be made of our parallaxes of galactic Cepheids, and 2) the determination of perturbation orbital elements for several exoplanet host stars, yielding true companion masses.