| 26th of November 2020 |
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| LBA observations of AB Dor A |
| by Climent et al. |
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Most Very Long Baseline Interferometry (VLBI) observations conducted
with the southern hemisphere Long Baseline Array (LBA) are of distant
Active Galactic Nuclei, or compact maser sources within our
Galaxy. However Climent et al. have recent described results from
observations of a nearby star system. Young stellar objects (YSOs)
exhibit radio emission as a result of a wide range of mechanisms. The
most common mechanisms occurs when electrons gyrate in the magnetic
fields of these objects, producing non-thermal continuum emission
through cyclotron, gyro-synchrotron, or synchrotron emission. The
radio emission in these objects is thought to originate in and remain
confined to the magnetosphere, with a typical size of a few stellar
radii.
About 15 parsecs (about 50 light years) away, AB Doradus (AB Dor) is one of the most active and extensively studied young stellar objects. It is a multiple system formed by two pairs of stars separated by 9 arcseconds, AB Dor A/C and AB Dor Ba/Bb. The main star of the system is AB Dor A, a dwarf of spectral type K0 that, with a period of only 0.5 days, is a fast rotator. AB Dor A dispalys strong emission at all wavelengths from radio to X-rays. The images above show three epochs at 8.4 GHz. All the images are centered, and cross-marked, at the expected positions of AB Dor A. For each image, the synthesized beam is shown at the bottom left corner. Radio emission from AB Dor A is evident, together with a component progressively moving away from the star. Climent et al. considered four different scenarios in order to explain this: a polar cap model, a flaring loop model, a helmet streamer model, and a close companion model. The results confirm the extraordinary coronal magnetic activity of this star, capable of producing compact radio structures at very large heights that have so far only been seen in binary interacting systems. The results are published in Astronomy and Astrophysics. |