J/A+A/641/A90 AB Dor A VLBI images (Climent+, 2020)
The milliarcsecond radio structure of AB Doradus A.
Climent J.B., Guirado J.C., Azulay R., Marcaide J.M., Jauncey D.L.,
Lestrade J.-F., Reynolds J.E.
<Astron. Astrophys. 641, A90 (2020)>
=2020A&A...641A..90C 2020A&A...641A..90C (SIMBAD/NED BibCode)
ADC_Keywords: Stars, pre-main sequence ; VLBI
Keywords: stars: coronae - stars: pre-main sequence - stars: imaging -
stars: flare - radio continuum: stars -
techniques: high angular resolution
Abstract:
The fast rotator, pre-main sequence star AB Dor A is a strong and
persistent radio emitter. The extraordinary coronal flaring activity
is thought to be the origin of compact radio emission and other
associated phenomena, such as large slingshot prominences.
We aim to investigate the radio emission mechanism and the
milliarcsecond radio structure around AB Dor A.
We performed phase-referenced VLBI observations at 22.3GHz, 8.4GHz,
and 1.4GHz over more than one decade using the Australian VLBI array.
Our 8.4GHz images show a double core-halo morphology, similar at all
epochs, with emission extending at heights between 5 and 18 stellar
radii. Furthermore, the sequence of the 8.4GHz maps shows a clear
variation of the source structure within the observing time. However,
images at 1.4GHz and 22.3GHz are compatible with a compact source.
The phase-reference position at 8.4GHz and 1.4GHz are coincident
with those expected from the well-known milliarcsecond-precise
astrometry of this star, meanwhile the 22.3GHz position is 4sigma off
the prediction in the north-west direction. The origin of this offset
is still unclear.
We have considered several models to explain the morphology and
evolution of the inner radio structure detected in AB Dor A. These
models include emission from the stellar polar caps, a flaring,
magnetically-driven loop structure, and the presence of helmet
streamers. We also investigated a possible close companion to AB Dor
A. Our 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.
Description:
Reduced images obtained with the VLBI array on 11 Nov. 2007, 25 Oct.
2010, 16 Aug. 2013, 14 Jun. 2017 and 6 Feb. 2018.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 197 13 List of fits files
fits/* . 13 Individual fits images
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 23 I4 --- Nx Number of pixels along X-axis
25- 28 I4 --- Ny Number of pixels along Y-axis
30- 39 A10 "date" Obs.date Observation date
41- 51 E11.6 Hz Freq Observed frequency
53- 57 I5 Kibyte size Size of FITS file
59- 83 A25 --- FileName Name of FITS file, in subdirectory fits
85-197 A113 --- Title Title of the FITS file
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Acknowledgements:
Juan Bautista Climent, j.bautista.climent(at)uv.es
(End) Patricia Vannier [CDS] 08-Sep-2020