Precision Timing of the Periodic Radio Flares from Ultracool Dwarf Stars

This award is to probe the internal structures and magnetic properties of ultracool dwarfs (UCDs) using precise timing of radio flares observed with the Arecibo radio telescope. UCDs are unusual objects which straddle the star-planet boundary. This group includes the lowest mass stars and brown dwarfs, and UCDs have temperatures ranging from about 1600-2700 K. Like many gas-giant planets and brown dwarfs, these relatively cool objects are thought to have dust clouds, and may generate magnetic fields through a rotating, convecting and electrically conducting fluid (also known as a 'magnetic dynamo'). Short-term periodic outbursts are observed at radio wavelengths, and in some cases their period decreases over time, sometimes very abruptly. The PI plans to analyze data showing these abrupt decreases in order to test models about the objects? interior structure, and also may be applicable to brown dwarfs and giant gas planets modeling. The PI plans to involve undergraduate female and underrepresented minority students, and provide them with well-structured opportunities to gain experience with plasma physics, astrophysics, observational techniques, advanced data analysis and instrumentation.

The planned radio detection of the UCDs provides a direct means to measure the field strength, topology and stability of low mass stars. Preliminary work by the PI shows that flaring period of two UCDs have been steadily decreasing, and that phase jumps have been observed a few months apart. After each jump, the period shortens significantly. This work will test whether it can be explained by differential rotation of the stars, in a manner analogous to sunspots in other main sequence stars.