at very young ages ($<$10 Myr) than the triangular H band peak. Both correlations differentiate young objects from field dwarfs, while the H$_{2}$(K) index can distinguish, at least statistically, populations of $\sim$1 Myr objects from populations of $\sim$10 Myr objects. We applied the H$_{2}$(K) index to NIFS data for one Orion nebula cluster (ONC) PMO and to previously published low resolution spectra for several other ONC PMOs where the 2.21 $\mu$m NaI doublet was unresolved and concluded that the average age of the PMOs is $\sim$1 Myr.'
author:
- |
    J. I. Canty$^{1}$[^1] P.W. Lucas$^{1}$ P.F. Roche$^{2}$ D.J. Pinfield$^{1}$\
    $^{1}$Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, AL10 9AB, UK\
    $^{2}$Astrophysics Department, University of Oxford, 1 Keble Road, Oxford OX1 3RH
title: Towards Precise Ages and Masses of Free Floating Planetary Mass Brown Dwarfs
---

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stars: formation $-$ stars: low-mass, brown dwarfs $-$ stars: luminosity function, mass function $-$ stars: pre-main-sequence.

Introduction
============

Deriving the substellar IMF requires a representative sample of objects whose ages are well-constrained. Evolutionary models can then be used to assign masses and radii to these objects. However, because cooling is more rapid for less massive bodies, brown dwarfs of any given effective 