Alpha2 Canum Venaticorum variable
Encyclopedia
An Alpha2 Canum Venaticorum variable (or α2 CVn variable) is a type of variable star
. These stars are chemically peculiar main sequence
star
s of spectral class
B8p to A7p. They have 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.
In addition to their intensities, the intensities and profiles of the spectral lines of α2 CVn variables also vary, as do their magnetic fields. The periods of these variations are all equal and are believed to equal the period of rotation
of the star. It is thought that they are caused by an inhomogeneous distribution of metals in the atmospheres
of these stars, so that the surface of the star varies in brightness from point to point.
The type-star which this class is named after is α² Canum Venaticorum, a star in the binary system of Cor Caroli, which is located in the northern constellation
of Canes Venatici
. Its brightness fluctuates by 0.14 magnitudes with a period of 5.47 days.
Variable star
A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
. These stars are chemically peculiar main sequence
Main sequence
The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s of spectral class
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
B8p to A7p. They have strong magnetic fields and strong silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
, strontium
Strontium
Strontium is a chemical element with the symbol Sr and the atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically. The metal turns yellow when exposed to air. It occurs naturally in the minerals celestine and...
, or chromium
Chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...
spectral lines. Their brightness typically varies by 0.01 to 0.1 magnitudes
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
over the course of 0.5 to 160 days.
In addition to their intensities, the intensities and profiles of the spectral lines of α2 CVn variables also vary, as do their magnetic fields. The periods of these variations are all equal and are believed to equal the period of rotation
Rotation
A rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...
of the star. It is thought that they are caused by an inhomogeneous distribution of metals in the atmospheres
Atmosphères
Atmosphères is a piece for full orchestra, composed by György Ligeti in 1961. It is noted for eschewing conventional melody and metre in favor of dense sound textures...
of these stars, so that the surface of the star varies in brightness from point to point.
The type-star which this class is named after is α² Canum Venaticorum, a star in the binary system of Cor Caroli, which is located in the northern constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
of Canes Venatici
Canes Venatici
Canes Venatici is one of the 88 official modern constellations. It is a small northern constellation that was created by Johannes Hevelius in the 17th century. Its name is Latin for "hunting dogs", and the constellation is often depicted in illustrations as representing the dogs of Boötes the...
. Its brightness fluctuates by 0.14 magnitudes with a period of 5.47 days.