Brown dwarfs (BD) were mere theoretical astrophysical objects for more than three decades (Kumar (1962)) till their first observational detection in 1995 (Rebolo et al. (1995), Nakajima et al. (1995)). These objects are intermediate in mass between stars and planets. Since their observational discovery these objects have been studied thoroughly and holistically. Various methods for searching and characterizing these objects in different regions of the sky have been put forward and tested with great success. Theoretical models describing their physical, atmospheric and chemical processes and properties have been proposed and have been validated with a large number of observational results.
The work presented in this dissertation is a compilation of synoptic studies of ultracool dwarfs(UDs)1. (1) A search for wide binaries around solar type stars in upper scorpio OB association (Upper Sco) do indicate (the survey is not yet complete) a deficit of BD binaries at these large separations (< 5AU</italic>). (2) Twenty six new UDs were discovered at low galactic latitudes in our survey from archival data and a novel technique using reduced proper motion. (3) Six field UDs were discovered by spectroscopic follow-up of the candidates selected from a deep survey. (4) Optical interferometry was used to independently determine the orbit of the companion of HD33636 which was initially determined using Hubble Space Telescope(HST) astrometry and radial velocity found. Some inconsistency in the HST determined orbit and mass. (5) Optical linear polarization in UDs was used to investigate the dust properties in their atmospheres. A trend in polarization as predicted by theoretical models was validated, and atmospheric dust grain sizes and projected rotational velocities for these objects were estimated.
Comprehensive studies of UDs are proving to be crucial not only in our understanding of UDs but also for star and planet formation as brown dwarfs represent their lower and upper mass boundaries, respectively.
1We use the term “ultracool dwarfs” as the mass of most of the objects mentioned is unknown, which is required to classify an object as a brown dwarf. We define objects later than M7 as ultra cool dwarfs.
|Advisor:||Martin, Eduardo L.|
|School:||University of Central Florida|
|School Location:||United States -- Florida|
|Source:||DAI-B 71/04, Dissertation Abstracts International|
|Keywords:||Brown dwarfs, Star formation, Ultracool dwarfs|
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