# The Changing Face of $\alpha$ Centauri B: Probing plage and stellar activity in K-dwarfs

## TL;DR

This study compares archival spectra of $ ext{α}$ Cen B during different activity states, revealing plage and spot signatures, radial velocity variations, and line broadening effects associated with stellar activity, aiding exoplanet detection and stellar dynamo understanding.

## Contribution

It provides the first detailed spectral comparison of $ ext{α}$ Cen B at different activity levels, identifying activity-related spectral features and their implications for stellar surface phenomena.

## Key findings

- Detection of rotationally modulated pseudo-emission features linked to plages and spots.
- Radial velocity variations of approximately 300 m/s associated with active regions.
- Broader spectral lines during high activity possibly due to magnetic bright points.

## Abstract

A detailed knowledge of stellar activity is crucial for understanding stellar dynamos, as well as pushing exoplanet radial-velocity detection limits towards Earth analogue confirmation. We directly compare archival HARPS spectra taken at the minimum in $\alpha$ Cen B's activity cycle to a high-activity state when clear rotational modulation of $\log{R'_{HK}}$ is visible. Relative to the inactive spectra, we find a large number of narrow pseudo-emission features in the active spectra with strengths that are rotationally modulated. These features most likely originate from plage, spots, or a combination of both. They also display radial velocity variations of $\sim$300 m s$^{-1}$ - consistent with an active region rotating across the stellar surface. Furthermore, we see evidence that some of the lines originating from the `active immaculate' photosphere appear broader relative to the `inactive immaculate' case. This may be due to enhanced contributions of e.g. magnetic bright points to these lines, which then causes additional line broadening. More detailed analysis may enable measurements of plage and spot coverage using single spectra in the future.