Multiwavelength Observations of AB Doradus

TL;DR

This study presents multiwavelength observations of AB Doradus, capturing large stellar flares and analyzing their spectral and polarimetric properties, revealing insights into active regions and flare mechanisms.

Contribution

It provides detailed multiwavelength data on stellar flares, including spectral hardening and polarization, during a coordinated campaign in 2006-2007, which is novel for this star system.

Findings

Significant spectral hardening during initial flare stages.

Detection of circular polarization in radio emissions.

Flares associated with a large active region near longitude zero.

Abstract

We have observed the bright, magnetically active multiple star AB Doradus in a multiwavelength campaign centring around two large facility allocations in November 2006 and January, 2007. Our observations have covered at least three large flares. These flares were observed to produce significant hardening of the X-ray spectra during their very initial stages. We monitored flare-related effects using the Suzaku X-ray satellite and the Australia Telescope Compact Array at 3.6 and 6 cm. Observations at 11 and 21 cm were also included, but they were compromised by interference. From our multiwavelength coverage we find that the observed effects can be mainly associated with a large active region near longitude zero. The second major X-ray and microwave flare of Jan 8, 2007 was observed with a favourable geometry that allowed its initial high-energy impulsive phase to be observed in the higher frequency range of Suzaku's XIS detectors. The fractional circular polarisation was measured for the complete runs, for 25 min integrations and, at 4.80 GHz, for 5 min integrations. Most of the full data sets showed circular polarisation fractions from AB Dor B that were significant at greater than the 3 sigma level. In several of the 5 min integrations at 4.80 and 8.64 GHz this fraction reached a significance level between 3 and 9 sigma. Lack of angular resolution prevented identification of these high V/I values with one or other of the two low-mass red-dwarf components of AB Dor B.