1. Protoplanet migration. A magnetic torque associated with the magnetic field linking a giant, gaseous protoplanet to its host pre-main-sequence star can halt inward protoplanet migration. This torque results from a toroidal magnetic field generated from the star’s poloidal (dipole) field by the twisting differential motion between the star’s rotation and the protoplanet’s revolution. Outside the corotation radius, where a protoplanet orbits slower than its host star spins, this torque transfers angular momentum from the star to the protoplanet, halting inward migration. Necessary conditions for angular momentum transfer include the requirement that the Alfvén speed in the region magnetically linking a protoplanet to its host star exceeds the protoplanet’s orbital speed. In addition, the timescale for Ohmic dissipation must exceed the protoplanet’s orbital period to ensure that the protoplanet is magnetically coupled to its host star. Inwardly migrating gaseous protoplanets can be expected to “pile up” very close to their central stars, as is indeed observed for extrasolar planets. The characteristic timescale required for a magnetic torque to transfer angular momentum outward from a more rapidly spinning central star to a magnetically coupled protoplanet is found to be comparable to planet-forming disk lifetimes and protoplanet migration timescales.
2. History of Science. Topics include the comet of Bethlehem and the mechanics of Nicole Oresme.
Stellar Photospheres. A stellar photosphere describes an outer layer of a star where the photons, after working their way out from the energy generating stellar core, finally escape into space. Some of these photons stream towards the Earth and have much to tell us about the physical conditions in stellar envelopes, particularly when collected by instruments with high spectral and spatial resolution. A star's evolution is controlled by fundamental parameters such as its mass, composition, rotation, and rate of mass-loss. The analysis of stellar photospheres constrains these parameters and tests state-of-the-art stellar models. The measurement of stellar photospheres is now being revolutionized by long-baseline interferometry which is for the first time producing spatially resolved, model-independent images of stars other than the Sun and yielding new insights.
Associate Professor, SP Program Coordinator
Dr. Jason Aufdenberg is a physical sciences associate professor and SP program coordinator in the Physical Sciences Department of Embry-Riddle Aeronautical University, Daytona Beach College of Arts & Sciences.
Edwin Mierkiewicz’s research focuses on the development and application of optical instrumentation for the study of terrestrial aeronomy, solar system astronomy, and the physics of the interstellar medium.