Statistical analysis of the population of brown dwarfs flaring in the radio range

(ORDO NEWS) — Brown dwarfs are also known as “failed stars” because they lack the processes of central thermonuclear hydrogen burning.

Some of the discovered brown dwarfs have magnetic fields of several kilogauss and show flare activity in the radio range, similar to the auroras that occur on planets in the solar system that have magnetic fields.

These facts aroused astronomers’ interest in studying the properties and dynamics of the fields of brown dwarfs.

Radio emission from brown dwarfs makes it possible to analyze their magnetic activity. In the case of solar-type stars, both radio, optical, and X-ray radiation are used for this purpose, while for brown dwarfs, which are extremely dim in visible and X-ray light, the most effective method for studying the properties of the magnetic field is the analysis of radio emission.

In the new work, Dr. Tang Jing of the National Astronomical Observatories of the Chinese Academy of Sciences, together with colleagues, performed a statistical analysis of the population of brown dwarfs exhibiting radio flare activity, which helped to quantify the potential for detecting such objects using FAST sky surveys.

The traditional method of studying brown dwarfs involves selecting a number of these objects and tracking them for several hours in order to detect possible flares – which is a very expensive undertaking.

So far, the number of discovered brown dwarfs exhibiting flare activity has been less than 20 objects. A new sky survey called the Commensal Radio Astronomy FAST Survey (CRAFTS) is expected to increase that number by almost an order of magnitude, according to the study.

Led by Dr. Li Di, who is also FAST project leader, the CRAFTS sky survey uses a new, never-before-seen mode for collaborative pulsar data collection, fast radio burst (FRB) searches, and mapping galaxies in HI hydrogen lines. The survey will cover 60 percent of the sky in drift-scan mode.

For the FAST sky survey, the main problem in determining the coordinates of a point source is that the position uncertainty is given by the width of the radiation flux, which sometimes turns out to be not narrow enough.

However, the radio emission emitted by flares exhibits a high degree of circular polarization, which reduces the uncertainty.

The parameters of circular polarization of radiation can be calculated from the orthogonally polarized resulting radiation, regardless of fluctuations in the system, and therefore this method is well suited for searching for flares.

If signals with a high level of circular polarization are detected during the survey, their identification will be based on the correlation with sources in the optical and infrared ranges, known from the archives of observations.

The FAST sky survey is expected to detect brown dwarfs exhibiting flare activity at distances up to 180 parsecs.

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