Broadly speaking, the process of star formation (SF) is now reasonably well understood in terms of hierarchical fragmentation of collapsing molecular clouds (Levy & Lunine 1983; Mannings, Boss & Russell 2001). In detail, however, there is no complete picture of SF (Shu et al. 1987). In particular, the spectrum of masses resulting from the SF process, commonly known as the initial mass function (IMF), cannot be predicted. This is unfortunate, because the IMF is a fundamental tool in studies of galaxy formation, stellar birthrate (Miller & Scalo 1979), the chemical evolution of galaxies (Cameron 1993) and the contribution of substellar objects to the total mass in stellar systems (Hambly, Knox & Hawkins 1999a). This last point is particularly interesting, since brown dwarfs (BDs; m<0.08M(sun)) have relatively high mass-to-light ratios at large ages and are not easily observed. It is only recently that small-scale, deep infrared studies have begun to tackle the question of the form of the very low mass IMF.
This proposal aims to measure the very low mass end of the stellar MF in a number of clusters and associations to masses m~0.01M(sun) (~10 M(Jup), units of Jupiter masses) in order to provide a firm footing for theoretical models and more general galactic studies. By measuring the MF in a number of Galactic environments and at a range of different ages, we aim to study the evolution of the MF over time, its relation to the IMF, and the universality (or otherwise) of this fundamental tool of stellar astrophysics.