A stellar magnetic field is a magnetic field generated by the motion of conductive plasma inside a star. This motion is created through convection, which is a form of energy transport involving the physical movement of material. A localized magnetic field exerts a force on the plasma, effectively increasing the pressure without a comparable gain in density. As a result, the magnetized region rises relative to the remainder of the plasma, until it reaches the star's photosphere. This creates starspots on the surface, and the related phenomenon of coronal loops.
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👉 Stellar magnetic field in the context of Heliophysics
Heliophysics (from the prefix "helio", from Attic Greek hḗlios, meaning Sun, and the noun "physics": the science of matter and energy and their interactions) is the physics of the Sun and its connection with the Solar System. NASA defines heliophysics as "(1) the comprehensive new term for the science of the Sun - Solar System Connection, (2) the exploration, discovery, and understanding of Earth's space environment, and (3) the system science that unites all of the linked phenomena in the region of the cosmos influenced by a star like our Sun."
Heliophysics is broader than Solar physics, that studies the Sun itself, including its interior, atmosphere, and magnetic fields. It concentrates on the Sun's effects on Earth and other bodies within the Solar System, as well as the changing conditions in space. It is primarily concerned with the magnetosphere, ionosphere, thermosphere, mesosphere, and upper atmosphere of the Earth and other planets. Heliophysics combines the science of the Sun, corona, heliosphere and geospace, and encompasses a wide variety of astronomical phenomena, including "cosmic rays and particle acceleration, space weather and radiation, dust and magnetic reconnection, nuclear energy generation and internal solar dynamics, solar activity and stellar magnetic fields, aeronomy and space plasmas, magnetic fields and global change", and the interactions of the Solar System with the Milky Way Galaxy.
In this Dossier
Stellar magnetic field in the context of Stellar rotation
Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface.
The rotation of a star produces an equatorial bulge due to centrifugal force. As stars are not solid bodies, they can also undergo differential rotation. Thus the equator of the star can rotate at a different angular velocity than the higher latitudes. These differences in the rate of rotation within a star may have a significant role in the generation of a stellar magnetic field.
Stellar magnetic field in the context of Alpha2 Canum Venaticorum variable
Alpha Canum Venaticorum variable (or α CVn variable) is a type of magnetic variable star. These are chemically peculiar stars of the CP2 type that are photometrically variable. That is, they are upper main sequence stars of spectral class B8p to A7p, with strong magnetic fields and strong silicon, strontium, or chromium spectral lines. Their brightness typically varies by 0.01 to 0.1 magnitudes over the course of 0.5 to 160 days.
The first CP2 variable to be discovered was α Canum Venaticorum, a star in the binary system of Cor Caroli, which lies in the northern constellation of Canes Venatici. Its brightness fluctuates by 0.14 magnitudes with a period of 5.47 days. This is now the prototype of the α CVn class of variables.
Stellar magnetic field in the context of Snow solar telescope
The Snow Solar Telescope is a solar telescope at the Mount Wilson Observatory in California. It was originally named the Snow Horizontal Telescope as it uses a coelostat to deflect light from the Sun into a fixed horizontal shed where it can be studied. The telescope was funded by a donation from Helen E. Snow of Chicago in 1903. It was assembled at Yerkes Observatory then transferred to Mt. Wilson in 1905.
This telescope is notable for the discovery that sunspots have a lower temperature than the photosphere, and for finding evidence they are associated with a magnetic field.