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Title: Radio emission from ultracool dwarfs and the relevant radiation mechanisms
Author: Yu, Shenghua
ISNI:       0000 0004 2745 5670
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2012
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Radio observations since July 2000 indicate that cool objects (temperature < 2500 K) can possess intense energy radiation at radio frequencies with very high brightness temperature and high degree of polarization. Statistically the quiescent radio emission has been detected from only ~9% of UCDs with spectral type later than M7 in a total sample number of ~193. TVLM 513- 46546, a long-term monitored M8.5 dwarf, not only shows a rotation modulated radio emission, but also presents complex functions between detected energy flux density, time and frequency. Coherent radiation may interpret the high brightness temperature. and high degree of polarization with the electron-cyclotron maser being the best candidate to fit the observed relations between the energy flux density, time and frequency. Based on the electron-cyclotron maser emission and the rotation of the dwarf, I have introduced an active region model for TVLM 513-46546 in this thesis. In this model, the physical properties of a plasma source, magnetic field on the dwarf, the properties of the active region are determined and discussed. The generation and propagation of X-ray emission is also discussed. Numerical simulations have also been done for understanding the generation and evolution of the radio emission. After setting up a grid for the initial parameters of plasma and magnetic field and running several series of simu1ations, I present the evolution of the radiated electromagnetic fields and their energy, the kinetic energy of particles, the growth rate and polarization of the radiated waves, and the spectrum of the radiated fields. The results of the simulations and their physical implication are shown in this thesis.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available