arXiv subjects

N. Eugene Engelbrecht

Publications and source records attributed to N. Eugene Engelbrecht.

4 recordsLinked to original sources

arXiv2026

Stellar Forcing of (exo)Planetary Environments

The environments of exoplanets are fundamentally shaped by the magnetic activity of their host stars through radiative, plasma, and particle-driven processes. This article presents a comprehensive overview of the four principal forms of stellar forcing that regulate atmospheric structure, chemistry, escape, and long-term planetary evolution: high-energy radiation, magnetized stellar winds, coronal mass ejections, and energetic particles. Using the Sun as a physically resolved benchmark, the discussion extends to increasingly active cool stars to establish a broader picture of star--planet interactions across the main sequence. The article first examines stellar X-ray and extreme ultraviolet emission from chromospheres and coronae, together with variability introduced by flares and magnetic reconnection. Particular attention is given to spectroscopic diagnostics, activity scalings with stellar rotation and age, flare energetics, and the observational links between impulsive and gradual phases of magnetic energy release. The treatment then shifts to magnetized stellar winds, describing the mechanisms that drive them and the role of multidimensional magnetohydrodynamic modeling in determining wind structure, angular momentum loss, and planetary interaction regimes. Solar and stellar coronal mass ejections are explored through their diagnostics, flare associations, propagation, and possible suppression by strong stellar magnetic fields. Finally, galactic and stellar energetic particles are discussed together with methods for estimating particle environments and their consequences for atmospheric chemistry and climate. The article concludes by outlining future observational and numerical developments needed to connect these coupled stellar forcing processes within a unified exoplanetary framework.

astro-ph.SR↗

arXiv2023

Impact of Cosmic Rays on Atmospheric Ion Chemistry and Spectral Transmission Features of TRAPPIST-1e

Ongoing observing projects like the James Webb Space Telescope (JWST) and future missions offer the chance to characterize Earth-like exoplanetary atmospheres. Thereby, M-dwarfs are preferred targets for transit observations, for example, due to their favorable planet-star contrast ratio. However, the radiation and particle environment of these cool stars could be far more extreme than what we know from the Sun. Thus, knowing the stellar radiation and particle environment and its possible influence on detectable biosignatures - particularly signs of life like ozone and methane - is crucial to understanding upcoming transit spectra. In this study, with the help of our unique model suite INCREASE, we investigate the impact of a strong stellar energetic particle event on the atmospheric ionization, neutral and ion chemistry, and atmospheric biosignatures of TRAPPIST-1e. Therefore, transit spectra for six scenarios are simulated. We find that a Carrington-like event drastically increases atmospheric ionization and induces substantial changes in ion chemistry and spectral transmission features: all scenarios show high event-induced amounts of nitrogen dioxide (i.e., at 6.2 $μ$m), a reduction of the atmospheric transit depth in all water bands (i.e., at 5.5 -- 7.0 $μ$m), a decrease of the methane bands (i.e., at 3.0 -- 3.5 $μ$m), and depletion of ozone (i.e., at $\sim$ 9.6 $μ$m). Therefore, it is essential to include high-energy particle effects to correctly assign biosignature signals from, e.g., ozone and methane. We further show that the nitric acid feature at 11.0 - 12.0 $μ$m, discussed as a proxy for stellar particle contamination, is absent in wet-dead atmospheres.

astro-ph.EP↗

arXiv2020

On the Generation of Compressible Mirror-mode Fluctuations in the Inner Heliosheath

Measurements made with the Voyager 1 spacecraft indicate that significant levels of compressive fluctuations exist in the inner heliosheath. Some studies have already been performed with respect to the mirror-mode instability in the downstream region close to the solar wind termination shock, and here we extend the investigation to the whole inner heliosheath. We employ quasilinear theory and results from a global magnetohydrodynamic model of the heliosphere to compute the time evolution of both the temperature anisotropy and the energy density of the corresponding magnetic fluctuations, and we demonstrate their likely presence in the inner heliosheath. Furthermore, we compute the associated, locally generated density fluctuations. The results can serve as inputs for future models of the transport of compressible turbulence in the inner heliosheath.

physics.space-ph↗

arXiv2020

On the Diversity of M-Star Astrospheres and the Role of Galactic Cosmic Rays Within

With upcoming missions such as the James Webb Space Telescope (JWST), the European Extremely Large Telescope (ELT), and the Atmospheric Remote-sensing Infrared Exoplanet Large-survey (ARIEL), we soon will be on the verge of detecting and characterizing Earth-like exoplanetary atmospheres for the first time. These planets are most likely to be found around smaller and cooler K- and M-type stars. However, recent observations showed that their radiation environment might be much harsher than that of the Sun. Thus, the exoplanets are most likely exposed to an enhanced stellar radiation environment, which could affect their habitability, for example, in the form of a hazardous flux of energetic particles. Knowing the stellar radiation field, and being able to model the radiation exposure on the surface of a planet is crucial to assess its habitability. In this study, we present 3D magnetohydrodynamic (MHD)-based model efforts investigating M-stars, focusing on V374 Peg, Proxima Centauri, and LHS 1140, chosen because of their diverse astrospheric quantities. We show that V374 Peg has a much larger astrosphere (ASP) than our Sun, while Proxima Centauri and LHS 1140 most likely have ASPs comparable or even much smaller than the heliosphere, respectively. Based on a 1D transport model, for the first time, we provide numerical estimates of the modulation of Galactic cosmic rays (GCRs) within the three ASPs. We show that the impact of GCRs on the Earth-like exoplanets Proxima Centauri b and LHS 1140 b cannot be neglected in the context of exoplanetary habitability.

astro-ph.SR↗