Brown dwarfs are “failed stars” due to their lack of central hydrogen burning, and they bridge the gap between planets and stars. Some brown dwarfs have been found to maintain kilogauss magnetic fields and produce blazing radio emissions, similar to auroras on magnetized planets in the solar system. This piqued astronomers’ curiosity about the properties and dynamics of their fields.
The radio emissions of brown dwarfs reflect their magnetic activities. Radio, optical, and X-ray emissions are used as magnetic tracers in solar-type stars. In contrast, in brown dwarfs, optical and X-ray emissions are dramatically reduced, and radio becomes the most effective probe.
Dr. Tang Jing and her colleagues at the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) performed a statistical analysis of the brown dwarf population with flash radiation that helped quantify the potential to find such objects in FAST surveys.
This study was published in Research in Astronomy and Astrophysics.
The traditional way to study brown dwarfs is to pick a few of them and watch them for several hours to pick up possible flares, which are very expensive. So far, the number of flaming brown dwarfs discovered has been less than 20. The so-called Commensal Radio Astronomy FAST Survey (CRAFTS) promises to increase the number by almost an order of magnitude, according to the study.
Under the leadership of Dr. Li Di, the principal scientist of FAST, CRAFTS uses a new and unprecedented mode to realize simultaneous data collection for pulsar and FRB searches, Galactic HI mapping, and HI galaxy. It is designed to cover 60% of the sky in drift-scan mode.
For FAST, the most significant problem in locating a point source is the confusion caused by the large beam size. However, the incoming radio emissions are highly circularly polarized and suffer from a minor disorder. Circular polarization can be calculated from orthogonally polarized outputs, independent of system fluctuation, and is a suitable method for finding flares.
If some highly circularly polarized signals are found in the survey, a cross-match to the archival optical/infrared counterpart can be used for identification. FAST is expected to detect up to 180 burning brown dwarfs.
Most flaming brown dwarfs are detected at high frequencies. Although some efforts have been made at low frequencies, incident L-band emission has not yet been detected. FAST can fill this gap. If successful, it also bodes well for FAST’s potential to discover exoplanets with strong magnetic fields.