Multi-wavelength observations of Proxima Centauri

TL;DR

This study presents simultaneous optical and X-ray observations of Proxima Centauri, revealing insights into its atmospheric conditions, magnetic activity, and flaring behavior through detailed spectral analysis and modeling.

Contribution

It provides the first detection of a weak optical Fe xiii line during active states and models the chromospheric response to flares using the PHOENIX code.

Findings

Detection of Fe xiii line at 3388 Å during active states

Identification of secondary flares possibly from neighboring loops

Temporal variations in H alpha line asymmetries during flares

Abstract

We report simultaneous observations of the nearby flare star Proxima Centauri with VLT/UVES and XMM-Newton over three nights in March 2009. Our optical and X-ray observations cover the star's quiescent state, as well as its flaring activity and allow us to probe the stellar atmospheric conditions from the photosphere into the chromosphere, and then the corona during its different activity stages. Using the X-ray data, we investigate variations in coronal densities and abundances and infer loop properties for an intermediate-sized flare. The optical data are used to investigate the magnetic field and its possible variability, to construct an emission line list for the chromosphere, and use certain emission lines to construct physical models of Proxima Centauri's chromosphere. We report the discovery of a weak optical forbidden Fe xiii line at 3388 AA during the more active states of Proxima Centauri. For the intermediate flare, we find two secondary flare events that may originate in neighbouring loops, and discuss the line asymmetries observed during this flare in H i, He i, and Ca ii lines. The high time-resolution in the H alpha line highlights strong temporal variations in the observed line asymmetries, which re-appear during a secondary flare event. We also present theoretical modelling with the stellar atmosphere code PHOENIX to construct flaring chromospheric models.