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Looking for Very Low-Mass Pre-Main Sequence Objects with SDSS

Published online by Cambridge University Press:  26 May 2016

Peregrine M. McGehee
MS H820, Los Alamos National Laboratory, Los Alamos, NM 87545
Suzanne L. Hawley
Department of Astronomy, Box 351580, University of Washington, Seattle, WA 98195
Kevin R. Covey
Department of Astronomy, Box 351580, University of Washington, Seattle, WA 98195


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Determining the process(es) by which brown dwarfs form is key to understanding their intrinsic nature. If their origins are within circumstellar disks they are akin to giant planets. If, on the other hand, they coalesce from molecular cloud cores, then they share a common lineage with low mass stars. These two mechanisms can be distinguished by investigation of young (< 10 Myr) substellar objects. If brown dwarfs are small failed stars, we expect to find very low mass analogs of the Classical T Tauris, with primordial magnetic fields from the molecular cloud collapse. Accretion onto these objects leads to characteristic magnetic activity signatures such as chromospheric and coronal emission resulting in an ultraviolet excess continuum.

The Orion OB1b association (m-M = 7.9, 2 Myr) provides a laboratory for following the strength and occurrence of the accretion process as a function of mass. Studies of the substellar mass function within the sigma Orionis cluster at the southern end of the association indicate that brown dwarfs are common. Based on model isochrones and the SDSS M dwarf sequence we expect the 95% completeness limit of the “Orion” scans to correspond to 0.1 and 0.03 solar masses for the u and g bands.

Part 9. Future Prospects
Copyright © Astronomical Society of the Pacific 2001 


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