Doppler imaging an X-ray flare on the ultrafast rotator BO Mic. A contemporaneous multiwavelength study using XMM-Newton and VLT

We present an analysis of contemporaneous photospheric, chromospheric and coronal structures on the

highly active K-dwarf star BO Mic (Speedy Mic). We concentrate on a moderate flare that we localize in the stellar

atmosphere and study its energetics, size and thermal behavior.

The analysis is based on strictly

simultaneous X-ray, UV- and optical observations carried out by XMM-Newton and the VLT.

We use Doppler imaging and related methods

for the localization of features.

Based on X-ray spectroscopy we study the

the coronal plasma in and outside the flare.

The flare emits in X-rays and UV, but is not detected in white light;

it is located at intermediate latitude between an extended spot group and

the weakly spotted pole. We estimate its height to be below 0.4 stellar radii, making it

clearly distinct in longitude and height from the prominences found

about two stellar radii above the surface.

In contrast to BO Mic's photospheric brightness,

neither its chromospheric nor its X-ray emission show a pronounced

rotational modulation.

Based on observations obtained at the ESO VLT Obs. No. 078.D-0865(A) and XMM-Newton Obs. Id. 0400460301 and 0400460401. Doppler imaging line profiles are only available in electronic form at http://www.aanda.org