X-ray emission from stars in the cool half of the Hertzsprung-Russell diagram is generally attributed to the presence of a magnetic corona that contains plasma at temperatures exceeding 1 million K. Coronae are ubiquitous among these stars, yet many fundamental mechanisms operating in their magnetic fields still elude an interpretation through a detailed physical description. Stellar X-ray astr...

We investigate the spatially-resolved star formation relation using a galactic disk formed in a comprehensive high-resolution (3.8 pc) simulation. Our new implementation of stellar feedback includes ionizing radiation as well as supernova explosions, and we handle ionizing radiation by solving the radiative transfer equation rather than by a subgrid model. Photoheating by stellar radiation stab...

We have studied the effect of hypothetical Cosmions on the core stability of main sequence stars (of populations I and II). Cosmions, with a mass of 4-10 Gev/c2 and a scattering cross section with nucleons of approximately 10-36 cm2 could prevail in transporting heat in the stellar cores. Raby [17] showed the existence of a local thermal instability caused by the presence of Cosmions in the sol...

We describe a relatively simple time-dependent convection model that can be coupled to the equations of radiation hydrodynamics. We show that it behaves in a physically plausible way in protostellar collapse flows and is quantitatively correct for nonlinear RR-Lyrae pulsations and the Sun. Together with the equations of radiation hydrodynamics the model closely approximates the classical stella...

It is now generally agreed that multidimensional, multigroup, radiation hydrodynamics is an indispensable element of any realistic model of stellar-core collapse, core-collapse supernovae, and proto-neutron star instabilities. We have developed a new, two-dimensional, multigroup algorithm that can model neutrino-radiation-hydrodynamic flows in core-collapse supernovae. Our algorithm uses an app...

Rossby waves (r-modes) in rapidly rotating neutron stars are unstable because of the emission of gravitational radiation. As a result, the stellar rotational energy is converted into both gravitational waves and r-mode energy. The saturation level for the r-mode energy is a fundamental parameter needed to determine how fast the neutron star spins down, as well as whether gravitational waves wil...

A defining property of massive stars is the dominant, dynamical role played by radiation throughout the stellar interior, atmosphere, and wind. Associated with this radiation hydrodynamics are several distinct kinds of instabilities that can lead to convection in both core and envelope, clumping in atmosphere and wind outflow, and perhaps even the dramatic mass loss outbursts associated with Lu...

The Earth’s atmosphere is a large scale laboratory to study particles. Particles from stellar processes impinge on the top of the Earth’s atmosphere and propagate downward. Particles from discharge processes at the bottom of the atmosphere propagate upwards into near-Earth space. The acceleration of both particle populations in the Earth’s atmosphere produces electromagnetic radiation which is ...