Parallaxes for Brown Dwarfs in Clusters

Summary

The prospects for direct parallax measurements of brown dwarfs and very low-mass stars in stellar clusters are bleak indeed. However, significant progress in parallaxes for nearby faint dwarfs, and for brighter stars in clusters can be expected in the next few years. The current state of play for ground- and space-based parallaxes is reviewed, along with the prospects for the future and the scientific questions we hope such observations will address.

Introduction

There is a tendency in the wider astronomical community to view astrometrists in general, and those who measure parallaxes in particular, as musty old fuddy-duddies doing valuable and worthy, if dull, work. This has always seemed to me a strange attitude, given that such observations set the foundations for almost all areas of astronomy. Personally, I find measuring parallaxes to be just about the most rewarding type of observation I've ever performed. There's a certain satisfaction to be had in measuring a fundamental quantity whose only model dependence is on Euclidean geometry - there aren't many other areas in astronomy where that's possible.

This general view of astrometry is particularly surprising in view of the phenomenal demand amongst the astronomical community for the rapid release of HIPPARCOS results. To my mind the constant discussion to be heard over observatory dinner tables world-wide asking “just when would the HIPPARCOS data go public?” reinforces the fact that such data is of fundamental importance to every field of astronomy – from the study of the faintest “non-quite stars”, to the study of galaxy formation and the early universe.