Using near-IR spectroscopy to classify substellar candidates in the Trapezium Cluster

Abstract

We discuss the use of near-IR spectroscopy to confirm young substellar candidates that were selected by photometry. We first review near-IR spectroscopic methods used to classify young brown dwarf candidates. In a subsequent part, we present ISAAC/VLT photometric and spectroscopic data of substellar candidates in the Trapezium Cluster. These data will be used to derive the effective temperature and reddening of the objects. We create a grid of synthetic spectra from Allard et al. (2000) with different degrees of reddening and compare those with our spectra, assuming a gravity of log g = [3.5, 4.0], which is typical for young objects. The best fitting reddened synthetic spectrum gives us the most likely effective temperature and extinction for our sources. Next, we compare the temperature derived from dereddening the objects towards a 1 Myr isochrone in a colour-magnitude diagram with the one obtained by fitting synthetic atmosphere models to the spectra, and show what extend the differences have when deriving the masses of the objects (under the assumption of an age of 1 Myr). (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)