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Title:
A spectroscopic survey of young brown dwarfs in the near-infrared
Authors:
McGovern, Mark Roland
Affiliation:
AA(University of California, Los Angeles, United States -- California)
Publication:
PhD Thesis, Proquest Dissertations And Theses 2005. Section 0031, Part 0606 244 pages; [Ph.D. dissertation].United States -- California: University of California, Los Angeles; 2005. Publication Number: AAT 3208386. DAI-B 67/02, Aug 2006
Publication Date:
00/2005
Origin:
UMI
Keywords:
Brown dwarfs, Near-infrared, Low-mass stars, Young stars
Comment:
Publication Number: AAT 3208386; ISBN: 0542567695; Advisor: McLean, Ian
Bibliographic Code:
2005PhDT........14M

Abstract

Motivated by the discovery of numerous Jupiter-sized brown dwarfs in infrared imaging surveys, and stimulated by the advent of sensitive near-infrared (NIR) spectrometers on very large telescopes, this thesis presents the results of a unique observational survey to investigate and characterize the near-infrared spectra of low-mass stars and brown dwarfs. The project, called the NIRSPEC Brown Dwarf Spectroscopic Survey (or BDSS) was carried out with the Keck 10- m telescope on Mauna Kea, Hawaii using the facility cryogenic NIR spectrometer (NIRSPEC) developed at UCLA by Professor Ian McLean. Beginning in April 1999, immediately after NIRSPEC was delivered to the telescope, this infrared spectroscopic survey was developed in multiple phases to obtain the largest self-consistent set of high quality spectra yet obtained for the two new classes of very cool objects known as L and T dwarfs (T eff ~ 2200-750K). This work presents the results of two of the major phases of the BDSS and includes near-infrared spectra from over 150 low-mass stars and brown dwarfs. In the first phase of the project the emphasis was on the effects of decreasing effective temperature (T eff ) on the infrared spectral morphology. Observations were concentrated on the J -band region of the spectrum from 1.14- 1.36 microns. Over 50 objects spanning the spectral types from M6 to T8 were observed in this band. With the spectral resolving power of the NIRSPEC instrument (R ~ 2000) we developed nine spectral indices to classify these objects in the J -band. From this data base it was possible for the first time to create a pure infrared spectral classification system for the L dwarfs, and to confirm the existing infrared classification system for T dwarfs. This is an important development because most of the flux from L and T dwarfs is radiated in the near-infrared, where they are several magnitudes brighter than at visible wavelengths, and classification via NIR properties is not only important but also essential as more distant and fainter brown dwarfs are discovered. In the second phase of the BDSS, called the Gravity Project, a new set of ~60 low-mass stars and substellar objects was studied. (Abstract shortened by UMI.)
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