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G. Schneider (Steward Obs., U. of Arizona), NICMOS IDT/EONS Team, STIS/8176 Team
Recently, many old isolated "field" brown dwarfs have been discovered from large ground-based surveys such as the 2-Micron All-Sky and Sloan Digital Sky surveys, and subsequently confirmed spectroscopically. Indeed, it has been suggested that brown dwarfs, once considered somewhat exotic objects, may be as common as stars. Yet, the companion mass fraction of these substellar objects which occupy a niche in the mass function between planets and stars remains largely unknown. How common are they? Do companion brown dwarfs form in a process more like planets than stars? How does the presence of a brown dwarf companion effect the evolution of a newly-forming solar system? To address these and related questions, during HST Cycle 7 the Near Infrared Camera and MultiObject Spectrometer Instrument Definition Team conducted a coronagraphic imaging survey designed to identify candidate substellar companions across the mass-spectrum bridging the stellar main sequence into the planetary domain. Now, as part of our follow-up observations we are using the Space Telescope Imaging Spectrograph to ascertain the physical nature of those candidates. Here we present the first results from that program, including spectra of likely 20 and 40 Jupiter mass companions to the young stars CD -33.7795 and HR 7329, respectively, and the somewhat older GL 577. While many more objects will have to be identified and studied to answer the questions fundamental posited above we believe these first steps are indicative of the bright prospects for continuing such investigations in the near future.
This work is based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc. under NASA contract NAS2-6555 and supported by NASA grants NAG5-3042 GO-98.8176A to the NICMOS IDT and EONS teams.