BY Draconis variable
Encyclopedia
BY Draconis variables are main sequence
variable star
s of late spectral types
, usually K or M. The name comes from the archetype for this category of variable star system, BY Draconis
. They exhibit variations in their luminosity
due to rotation of the star
coupled with star spots, and other chromospheric
activity. Resultant brightness fluctuations are generally less than 0.5 magnitudes
on timescales equivalent to the star's rotational period, typically from a fraction of a day to several months. Some of these stars may also have flares, resulting in additional variations of the UV Ceti type. Oddly enough, Procyon
the 8th brightest night-time star which is an F5 sub-giant or dwarf has also been classified as a BY Draconis variable. (Source : Schaaf, The Brightest Stars, Wiley, 2008.)
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...
variable star
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...
s of late spectral types
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...
, usually K or M. The name comes from the archetype for this category of variable star system, BY Draconis
BY Draconis
BY Draconis is a multi-star system in the constellation Draco. It consists of at least three components. Components A and B form a close binary star system with a short orbital period of only 5.98 days. These may be pre-main sequence objects that are still in the process of collapsing. Their...
. They exhibit variations in their luminosity
Luminosity
Luminosity is a measurement of brightness.-In photometry and color imaging:In photometry, luminosity is sometimes incorrectly used to refer to luminance, which is the density of luminous intensity in a given direction. The SI unit for luminance is candela per square metre.The luminosity function...
due to rotation of the 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...
coupled with star spots, and other chromospheric
Chromosphere
The chromosphere is a thin layer of the Sun's atmosphere just above the photosphere, roughly 2,000 kilometers deep....
activity. Resultant brightness fluctuations are generally less than 0.5 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...
on timescales equivalent to the star's rotational period, typically from a fraction of a day to several months. Some of these stars may also have flares, resulting in additional variations of the UV Ceti type. Oddly enough, Procyon
Procyon
Procyon is the brightest star in the constellation Canis Minor. To the naked eye, it appears to be a single star, the seventh brightest in the night sky with a visual apparent magnitude of 0.34...
the 8th brightest night-time star which is an F5 sub-giant or dwarf has also been classified as a BY Draconis variable. (Source : Schaaf, The Brightest Stars, Wiley, 2008.)