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Title: Properties of the radio emission at the stellar/substellar boundary.
Author: Antonova, Antoaneta Emilova.
ISNI:       0000 0001 3425 4605
Awarding Body: Queen's University of Belfast
Current Institution: Queen's University Belfast
Date of Award: 2008
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number of ultracool dwarfs have been detected as relatively bright sources at radio frequencies. Initially, the detection of variable, broadband radio emission with low net circular polarization suggested incoherent gyrosynchrotron radiation due to a population of electrons spiraling in the magnetic field of the dwarf. This is the mechanism by which higher mass dwarf stars are thought to generate persistent levels of radio emission. However, such stars are surrounded by high temperature chromospheres and coronae. Ultracool dwarfs, on the other hand, are thought to possess cooler, more neutral atmospheres, as evidenced by their low H~and X-ray luminosities, and yet can produce high levels of radio emission. The VLA observations of the ultracool dwarf TVLM 513, presented in this thesis resulted in the detection of both rotational modulation and periodic, extremely bright and highly circularly polarized bursts of radio emission which strongly suggest that the dominant radio emission mechanism in these objects might be the coherent electron cyclotron maser. The observations of several other ultracool dwarfs indicate that they can also display long-term sporadic variability in their persistent emission. The observation of pulsed coherent emission from ultracool dwarfs is, in effect, the discovery of a completely new category of radio emitting objects and has immense implications for our understanding of both stellar magnetic activity and the dynamo mechanism generating magnetic fields in fully convective stars and brown dwarfs. It is a significant departure from the gyrosynchrotron model gerwrally applied to cool stars and, in fact, has more in common with the coherent radio emission observed from all of the magnetized planets in our solar system. Supplied by The British Library - 'The world's knowledge'
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available