Searching for benchmark ultracool dwarfs (Avril Day-Jones, Universidad de Chile)

Since the discovery of the first brown dwarfs (Tiede1; Reblo et al., 1995; Gliese 229B; Nakajima et al., 1995) a population of more than 700 are now identified in our local stellar vicinity (<150pc). However our understanding of these ultracool objects is still somewhat lacking. Their atmospheres provide the right environment for clouds of water vapour, methane and silicate dust to form, and make modelling a difficult task. As a result existing atmospheric models struggle to accurately predict the range of observed photometric and spectroscopic properties. What is needed is a set of benchmark objects to aid the calibration of the models. These benchmark objects will also be help answer many unanswered questions relating to ultracool dwarfs, such as; what is the shape of the low-mass IMF and has it varied over the age of the galactic disk? does brown dwarf formation follow star formation, or does it have some other form? what is the current birth rate of ultracool objects, and is the shape of the IMF or the formation affected by metallicity?

Our aim is to identify a population of benchmark objects, whose properties (e.g. age, distance, metallicity) can be directly inferred without the need to refer to models. Such populations may be found as members of young clusters, kinematic moving groups or as members of binary systems, where the primary member has a well calibrated age. I will present the current status of the ultracool benchmark population, as well as our ongoing searches for such benchmarks in members binary systems.