Mercury-manganese star
Encyclopedia
A mercury-manganese star is a type of chemically peculiar star
with a prominent spectral line at 398.4 nm
, due to absorption from ionized mercury
. These stars are of spectral type B8 or B9, with two distinctive characteristics:
Their rotation is relatively slow, and as a consequence their atmosphere
is relatively calm. Some types of atoms sink under the force of gravity, while others are lifted towards the exterior of the star by radiation pressure
, making an inhomogeneous atmosphere.
The following table includes the brightest stars in this group.
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...
with a prominent spectral line at 398.4 nm
Nanometre
A nanometre is a unit of length in the metric system, equal to one billionth of a metre. The name combines the SI prefix nano- with the parent unit name metre .The nanometre is often used to express dimensions on the atomic scale: the diameter...
, due to absorption from ionized mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
. These stars are of spectral type B8 or B9, with two distinctive characteristics:
- An atmospheric excess of elements like phosphorusPhosphorusPhosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
, manganeseManganeseManganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...
, galliumGalliumGallium is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium salt in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. As it liquefies...
, strontiumStrontiumStrontium 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...
, yttriumYttriumYttrium is a chemical element with symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and it has often been classified as a "rare earth element". Yttrium is almost always found combined with the lanthanides in rare earth minerals and is...
, zirconiumZirconiumZirconium is a chemical element with the symbol Zr and atomic number 40. The name of zirconium is taken from the mineral zircon. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium...
, platinumPlatinumPlatinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...
and mercuryMercury (element)Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
. - A lack of a strong magnetic fieldMagnetic fieldA magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
.
Their rotation is relatively slow, and as a consequence their atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
is relatively calm. Some types of atoms sink under the force of gravity, while others are lifted towards the exterior of the star by radiation pressure
Radiation pressure
Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. If absorbed, the pressure is the power flux density divided by the speed of light...
, making an inhomogeneous atmosphere.
The following table includes the brightest stars in this group.
| Name | |Bayer Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek letter, followed by the genitive form of its parent constellation's Latin name... or Flamsteed designation Flamsteed designation Flamsteed designations for stars are similar to Bayer designations, except that they use numbers instead of Greek letters. Each star is assigned a number and the Latin genitive of the constellation it lies in... | |Spectral type | Apparent visual magnitude |
|---|---|---|---|
| Alpheratz | α Andromedae | B8IVmnp | 2.06 |
| Gienah Corvi | γ Corvi | B8III | 2.59 |
| Maia | 20 Tauri | B8III | 3.87 |
| χ Lupi | B9IV | 3.96 | |
| Muliphein | γ Canis Majoris | B8II | 4.10 |
| φ Herculis | B9mnp | 4.23 | |
| π1 Bootis | B9p | 4.91 | |
| ι Coronae Borealis | A0p | 4.98 | |
| κ Cancri A | B8IIImnp | 5.24 | |
| Dabih Minor | β Capricorni B | B9.5III/IV | 6.10 |