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Published February 16, 2009 | Published
Book Section - Chapter Open

Mapping the Radio Coronae of Cool Stars and Brown Dwarfs


The pulsing radio emission detected from ultracool dwarfs can be used as a powerful diagnostic of magnetic field strengths and topologies at and below the substellar boundary. Studies thus far have confirmed magnetic field strengths of 3 kG for two late M dwarfs and 1.7 kG for an L3.5 dwarf, the latter being the first confirmation of kG magnetic fields for an L dwarf. Ongoing long term monitoring of the radio pulses will also investigate the stability of the associated large‐scale magnetic fields over timescales > 1  year. We also present the preliminary results of a lengthy radio monitoring campaign of the rapidly rotating M4 star V374 Peg, with the resulting light curves phased with magnetic maps previously obtained through Zeeman Doppler Imaging. The radio emission from V374 Peg is strongly modulated by the large scale dipolar magnetic field, with two clear peaks in the radio light curve per period of rotation, occurring when the dipolar field lies in the plane of the sky. These results provide strong evidence that the electron cyclotron maser instability plays a pivotal role in the production of quiescent radio emission from V374 Peg, representing a significant departure from the accepted model of gyrosynchrotron emission as the dominant source of quiescent radio emission from active M dwarfs.

Additional Information

© 2009 American Institute of Physics. Published online 16 February 2009. We would like to thank the organisers of Cool Stars 15 for the opportunity to present these results. GH and AG gratefully acknowledge the support of Science Foundation Ireland (Grant Number 07/RFP/PHYF553). Armagh Observatory is grant aided by the N. Ireland Dept. of Culture, Arts & Leisure.

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