Observations of X-ray flares and associated MHD oscillations in star XI Boo

TL;DR

This study analyzes X-ray flares in star XI Boo using XMM-Newton data, revealing magnetoacoustic oscillations in stellar loops, which provides new observational evidence of fast-kink mode oscillations in stellar coronae.

Contribution

It presents the first observational evidence of fast-kink mode oscillations in stellar loops during the post-flare phase, using wavelet analysis and hydrodynamic modeling.

Findings

Detected 1019 s oscillations in X-ray light curves.

Derived loop lengths smaller than the stellar radius.

Theoretically matched oscillation periods with observations.

Abstract

Using data from observations made with XMM-Newton, we present an X-ray analysis of two flares observed in $\xi$ Boo. The flare loop parameters are derived using various loop models including state-of-the-art hydrodynamic flare model. The loop lengths derived for the flaring loop structure are found to be less than the stellar radius. The exponential decay of the X-ray light curves, and time evolution of the plasma temperature and emission measure are similar to those observed in compact solar flares. The X-ray light curve of post flare phase is investigated with wavelet analysis. Wavelet analysis clearly show oscillations of the period of 1019 s. Using the observationally estimated loop length, density and magnetic field, the theoretically derived oscillation period for fast-kink mode approximately matches with the observationally estimated period. This is the first likely observational evidence of fundamental fast-kink mode of magnetoacoustic waves in the stellar loops during the post-flare phase of heightened emission.