2023 Fall Schedule

Title:  Extreme space weather and a clock for the solar cycle

Abstract: Geomagnetic storms have the potential for significant impact on a wide range of technologies and a particular challenge is quantifying the occurrence likelihood of extreme storms which, by definition, are rare events. The likelihood of occurrence of geomagnetic storms varies with the solar cycle and each cycle has a unique amplitude and duration. Whilst there are comprehensive high fidelity observations of the sun, solar wind and geomagnetic response at earth over the last four to five solar cycles, observations that extend over multiple cycles are more limited. Nevertheless, historical ground magnetic observations over the last 150 years can be used to quantify space weather risk. They can be combined with the sunspot record to construct a uniform ‘clock’ for space weather activity which reveals a fast switch-on (and off) between the relatively quiet conditions around solar minima, and more active conditions around solar maxima. The clock provides a framework to predict the switch-on and off times, imperative since some of the most extreme events have occurred right at the switch-on. Links can be made between timings of activity from the solar clock, and global solar morphology, bridging between the evolution of the solar dynamo, and space weather activity at earth.

Title: Low energy cosmic rays in the interstellar medium

Abstract: Low-energy cosmic rays (up to the GeV energy domain) play a crucial role in the physics and chemistry of the densest phase of the interstellar medium. Unlike interstellar ionising radiation, they can penetrate large column densities of gas, and reach molecular cloud cores. By maintaining there a small but not negligible gas ionisation fraction, they dictate the coupling between the plasma and the magnetic field, which in turn affects the dynamical evolution of clouds and impacts on the process of star and planet formation. The cosmic-ray ionisation of molecular hydrogen in interstellar clouds also drives the rich interstellar chemistry revealed by observations of spectral lines in a broad region of the electromagnetic spectrum, spanning from the submillimetre to the visual band. Some recent developments in various branches of astrophysics provide us with an unprecedented view on low-energy cosmic rays. Accurate measurements and constraints on the intensity of such particles are now available both for the very local interstellar medium and for distant interstellar clouds. The interpretation of these recent data is currently debated, and the emerging picture calls for a reassessment of the scenario invoked to describe the origin and/or the transport of low-energy cosmic rays in the Galaxy.

Title: Imaging Stellar Surfaces

Abstract: One way that the stellar magnetism of convective-envelope stars manifests is as starspots, which are localized regions of stifled convection appearing dark on stellar surfaces.  These cool surface features can affect the measurements of a star's fundamental stellar parameters, including radius and temperature, which ultimately lead to inaccurate estimates of mass and age.  Starspots also can mimic or obscure the detections of exoplanets.  As a result, an improved understanding of stellar surfaces is needed to be able to detect Earth-like planets around quiet Sun-like stars.  My work aims to use images of stellar surfaces to better understand stellar activity and to help disentangle the signatures of stars and their exoplanets.  I will discuss the imaging techniques I use and my on-going project to image some of the closest  stars with sub-milliarcsecond resolution interferometric data.  I will also discuss how some of these surface images are used to model radial velocities for comparison with contemporaneous extreme precision radial velocity observations to improve our understanding of how stellar magnetism impacts the evidence and characterization of companions.