Indications of stellar prominence oscillations on fast rotating stars: the cases of HK Aqr and PZ Tel

TL;DR

This study investigates stellar prominence oscillations on young, fast-rotating stars HK Aqr and PZ Tel through spectroscopic monitoring, revealing sinusoidal prominence motions and estimating magnetic field strengths.

Contribution

It provides the first evidence of prominence oscillations on these stars and estimates magnetic field strengths based on prominence dynamics.

Findings

Detection of sinusoidal prominence oscillations on HK Aqr.

No periodic oscillations detected on PZ Tel.

Estimated magnetic field strength of ~2G for HK Aqr prominence.

Abstract

We present the analysis of six nights of spectroscopic monitoring of two young and fast rotating late-type stars, namely the dMe star HK Aqr and the dG/dK star PZ Tel. On both stars we detect absorption features reminiscent of signatures of co-rotating cool clouds or prominences visible in H$\alpha$. Several prominences on HK Aqr show periodic variability in the prominence tracks which follow a sinusoidal motion (indication of prominence oscillations). On PZ Tel we could not find any periodic variability in the prominence tracks. By fitting sinusoidal functions to the prominence tracks we derive amplitudes and periods which are similar to those of large amplitude oscillations seen in solar prominences. In one specific event we also derive a periodic variation of the prominence track in the H$\beta$ spectral line which shows an anti-phase variation with the one derived for the H$\alpha$ spectral line. Using these parameters and estimated mass density of a prominence on HK Aqr we derive a minimum magnetic field strength of $\sim$2G. The relatively low strength of the magnetic field is explained by the large height of this stellar prominence ($\ge$ 0.67 stellar radii above the surface).