Spectral Tomography of Ultra-Cool Dwarf Radio Magnetospheres

University Of Iowa, Iowa City IA

Investigators

Abstract

The primary scientific goal of the project is to determine the structure of magnetic fields in very low-mass stars. This study will broaden our understanding of how magnetic fields are generated in stars, which is currently not well understood. This could also contribute to our understanding of the Sun's magnetic field, which plays a key role in the potentially damaging solar magnetic storms that reach Earth during periods of high solar activity. The program will provide a graduate training opportunity for a student from a group that is underrepresented in astronomy. Results from this program will be integrated into a new undergraduate course being developed by the PI. This proposal addresses a fundamental question in stellar astrophysics: What is the nature of the surprisingly strong coronal magnetic fields in very low-mass stars? The research program comprises two parts. The first is an observational program to determine the dynamical spectra of a selected sample of ultra-cool dwarf stars that exhibit pulsed radio emission. The observations will utilize the Very Large Array to obtain wideband spectra over several epochs to establish the stability of the pulse periods, polarization, and morphology. The second part is the development of a realistic magnetospheric model that will be used to create synthesized wideband spectra. The model will include several plasma physics effects that have not been previously considered, such as cold-plasma ray tracing and angular beaming caused by density-depleted cavities. This scheme, denoted spectral tomography, will compare synthetic dynamic spectra with observations to constrain the geometry and plasma properties of the stellar magnetospheres.