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A coronal mass ejection (CME) is a significant ejection of magnetic field and accompanying plasma mass from the Sun's corona into the heliosphere. CMEs are often associated with solar flares and other forms of solar activity, but a broadly accepted theoretical understanding of these relationships has not been established.
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An active region is a temporary region in the Sun's atmosphere characterized by a strong and complex magnetic field. They are often associated with sunspots and are commonly the source of violent eruptions such as coronal mass ejections and solar flares. The number and location of active regions on the solar disk at any given time is dependent on the solar cycle.
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The thick disk is one of the structural components of about 2/3 of all disk galaxies, including the Milky Way. It was discovered first in external edge-on galaxies. Soon after, it was proposed as a distinct galactic structure in the Milky Way, different from the thin disk and the halo in the 1983 article by Gilmore & Reid. It is supposed to dominate the stellar number density between 1 and 5 kiloparsecs above the galactic plane and, in the solar neighborhood, is composed almost exclusively of older stars. Its stellar chemistry and stellar kinematics are also said to set it apart from the thin disk. Compared to the thin disk, thick disk stars typically have significantly lower levels of metals—that is, the abundance of elements other than hydrogen and helium.
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Solar radio emission refers to radio waves that are naturally produced by the Sun, primarily from the lower and upper layers of the atmosphere called the chromosphere and corona, respectively. The Sun produces radio emissions through four known mechanisms, each of which operates primarily by converting the energy of moving electrons into electromagnetic radiation. The four emission mechanisms are thermal bremsstrahlung (braking) emission, gyromagnetic emission, plasma emission, and electron-cyclotron maser emission. The first two are incoherent mechanisms, which means that they are the summation of radiation generated independently by many individual particles. These mechanisms are primarily responsible for the persistent "background" emissions that slowly vary as structures in the atmosphere evolve. The latter two processes are coherent mechanisms, which refers to special cases where radiation is efficiently produced at a particular set of frequencies. Coherent mechanisms can produce much larger brightness temperatures (intensities) and are primarily responsible for the intense spikes of radiation called solar radio bursts, which are byproducts of the same processes that lead to other forms of solar activity like solar flares and coronal mass ejections.
The Alfvén surface is the boundary separating a star's corona from the stellar wind defined as where the coronal plasma's Alfvén speed and the large-scale stellar wind speed are equal. It is named after Hannes Alfvén, and is also called Alfvén critical surface, Alfvén point, or Alfvén radius. Parker Solar Probe became the first spacecraft that crossed Alfvén surface of the Sun.
Gordon Dean Holman is an emeritus research astrophysicist at the National Aeronautics and Space Administration's (NASA’s) Goddard Space Flight Center in Greenbelt, Maryland. His research mostly focused on obtaining an understanding of high-energy radiation from astronomical objects. This radiation cannot be observed from Earth's surface, but is observed with instruments on satellites launched to orbits above Earth's atmosphere. It is primarily emitted by high-energy electrons interacting with ions. These electrons also emit radiation at radio frequencies which is observed from Earth's surface. Consequently, these observations from space and radio telescopes provide a view of hot gas and energetic particles in the Universe that could not otherwise be obtained. Holman has specialized in the interpretation of these observed emissions to determine the origin and evolution of this hot gas and energetic particles. He has been described as "not just a theorist, he also looks at the data".
References
- ↑ "SPD Harvey Prize Citations". spd.aas.org. Archived from the original on 2016-05-26. Retrieved 2016-06-18.
- ↑ Reeves, Katharine K.; Golub, Leon (2011). "Atmospheric Imaging Assembly Observations of Hot Flare Plasma". The Astrophysical Journal. 727 (2): L52. Bibcode:2011ApJ...727L..52R. doi: 10.1088/2041-8205/727/2/L52 . S2CID 121213510.
- ↑ Savage, Sabrina L.; et al. (2023). "The First Flight of the Marshall Grazing Incidence X-Ray Spectrometer (MaGIXS)". The Astrophysical Journal. 945 (2): 105. arXiv: 2212.00665 . Bibcode:2023ApJ...945..105S. doi: 10.3847/1538-4357/acbb58 . S2CID 126230776.
- ↑ Winebarger, A. R.; De Pontieu, B.; Cheung, C. M. M.; Martinez-Sykora, J.; Hansteen, V. H.; Testa, P.; Golub, L.; Savage, S. L.; Samra, J.; Reeves, K. (2019). "Unfolding Overlappogram Data: Preparing for the COOL-AID instrument on Hi-C FLARE". AGU Fall Meeting Abstracts. 2019. Bibcode:2019AGUFMSH33A..06W.
- ↑ "Reeves, Katharine". Smithsonian Institution. Retrieved 24 October 2019.
- ↑ "Kathy Reeves Awarded the 2016 Karen Harvey Prize for Solar Astronomy". www.cfa.harvard.edu/. 2015-12-17. Retrieved 2016-06-18.
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