Astrometry as a Tool for Discovering and Weighing Faint Companions to Nearby Stars

TL;DR

This paper explains how absolute astrometry from Hipparcos and Gaia can be used to discover faint companions to nearby stars and measure their masses and orbits, highlighting the method's sensitivity and data requirements.

Contribution

It provides a comprehensive tutorial on using astrometry for detecting and characterizing faint stellar companions, including data interpretation and orbit fitting techniques.

Findings

Astrometry can detect companions with long orbital periods.

Mass and orbit measurements are feasible for faint companions.

Sensitivity depends on stellar and companion properties.

Abstract

This tutorial covers the use of absolute astrometry, in particular from the combination of the Hipparcos and Gaia missions, to identify faint companions to nearby stars and to measure the masses and orbits of those companions. Absolute astrometry has been used with increasing success to discover new planets and brown dwarfs and to measure masses and orbits for systems with periods as long as centuries. This tutorial summarizes the nature of the underlying astrometric data, the approach typically used to fit orbits, and the assumptions about that data implicit throughout the process. It attempts to provide intuition for the sensitivity of astrometry as a function of stellar and companion properties and how the available constraints depend on the character and quantity of data available. This tutorial is written for someone with some background in astronomy but with no more than a minimal acquaintance with astrometry or orbit fitting.