Seminario: W.M. Joseph (Universität Tübingen)
Titolo: Investigating the Solar-Stellar Analogy: The flare star AD Leo compared to our Sun
Speaker: W.M. Joseph (Institut für Astronomie & Astrophysik, Eberhard Karls Universität Tübingen)
Abstract: The solar corona is often invoked as a template for stellar ones, but the significant difference between solar and non-solar instruments and data makes direct comparison between X-ray observations of the Sun, which is usually of the resolved solar disk, and stellar point-source observations almost impossible. In order to overcome this hurdle, the research group at INAF Osservatorio Astronomico di Palermo has devised a method in which solar X-ray data is converted to a format which is virtually identical to that of actual stellar X-ray observations (called the Sun-as-an-Xray-star, SaXS, method; e.g., Peres+2000, ApJ 528).
First applications of the Sun-as-an-Xray-star method have used a grid of synthetic “stellar-like” X-ray spectra based on emission measures for different types of solar coronal structures like background corona, active regions, cores of active regions and flares. The target star’s coronal filling factor with these regions was then found by finding the grid-point closest to the observed X-ray spectrum of the star (e.g., Coffaro+2020). We have now further developed this method into spectral models using XSPEC that correspond to the different solar magnetic structures (background corona, active regions, cores of active regions and flares). Using these models, the hypothetical filling factors of these regions can be recovered.
For the first time, we apply the Sun-as-an-Xray-star method to a star which significantly differs from our Sun, AD Leo, in order to investigate how far the postulated solar-stellar analogy can be stretched. The early-M dwarf AD Leo is the ideal benchmark for stellar activity in the low-mass regime and its influence on planet atmospheres due to its proximity (5 pc) and high activity level, allowing for high-signal X-ray observations. In this project, we aim to reconstruct an X-ray corona of AD Leo, assuming it is covered by solar magnetic structures. We apply the XSPEC implementation of the Sun-as-an-Xray-star method to AD Leo spectra from eROSITA and XMM-Newton, and investigate the results of its application.