Mu Cassiopeiae, Latinized from μ Cassiopeiae, is a

binary star A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...

system in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Cassiopeia Cassiopeia or Cassiopea may refer to: Greek mythology * Cassiopeia (mother of Andromeda), queen of Aethiopia and mother of Andromeda * Cassiopeia (wife of Phoenix), wife of Phoenix, king of Phoenicia * Cassiopeia, wife of Epaphus, king of Egy ...

. This system shares the name Marfak with

Theta Cassiopeiae Theta Cassiopeiae or θ Cassiopeiae is a solitary star in the northern constellation of Cassiopeia (constellation), Cassiopeia. It shares the traditional name Marfak with μ Cassiopeiae, positioned less than half a degree to the WSW, w ...

, and the name was from Al Marfik or Al Mirfaq (المرفق), meaning "the elbow". It is dimly visible to the naked eye as a point of light with an

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light ca ...

of 5.16. The system is located at a distance of 25

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s from the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

based on

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...

, and is moving closer with a high

radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity ...

of −97 km/s. This star will move into the constellation

Perseus In Greek mythology, Perseus (, ; Greek language, Greek: Περσεύς, Romanization of Greek, translit. Perseús) is the legendary founder of the Perseid dynasty. He was, alongside Cadmus and Bellerophon, the greatest Greek hero and slayer of ...

around 5200 AD. Mu Cassiopeiae is given as a standard star for the

spectral class In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

G5Vb, although it is frequently described as a

subdwarf A subdwarf, sometimes denoted by "sd", is a star with luminosity class VI under the Yerkes spectral classification system. They are defined as stars with luminosity 1.5 to 2 magnitudes lower than that of main-sequence stars of the same ...

, meaning it has a luminosity below that expected for a G5

main sequence In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...

star. The

metallicity In astronomy, metallicity is the Abundance of the chemical elements, abundance of Chemical element, elements present in an object that are heavier than hydrogen and helium. Most of the normal currently detectable (i.e. non-Dark matter, dark) matt ...

, or abundance of heavy elements, is about one-sixth that in the Sun. It is slightly smaller than the Sun with less mass and a lower luminosity. It is among the oldest known stars, with an age of billion years making it possibly the oldest star visible to the unaided eye. This is one of the first high-velocity stars to be identified. Compared to other nearby stars including the Sun, this pair are moving at a relatively high velocity of 167 km/s through the

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

galaxy A galaxy is a Physical system, system of stars, stellar remnants, interstellar medium, interstellar gas, cosmic dust, dust, and dark matter bound together by gravity. The word is derived from the Ancient Greek, Greek ' (), literally 'milky', ...

. They are low metal,

Population II In 1944, Walter Baade categorized groups of stars within the Milky Way into stellar populations. In the abstract of the article by Baade, he recognizes that Jan Oort originally conceived this type of classification in 1926. Baade observed th ...

stars that are thought to have formed before the galactic disk first appeared.

Companions

There are five visible companions to Mu Cassiopeiae listed in the

Washington Double Star Catalog The Washington Double Star Catalog, or WDS, is a catalog of double stars, maintained at the United States Naval Observatory. The catalog contains positions, magnitudes, proper motions and spectral types and has entries for (as of January 2024) 1 ...

. All are distant background objects fainter than 11th magnitude. The brightest of these is catalogued as component B, but the very high

proper motion Proper motion is the astrometric measure of changes in the apparent places of stars or other celestial objects as they move relative to the center of mass of the Solar System. It is measured relative to the distant stars or a stable referenc ...

of Mu Cassiopeiae has caused it to almost double its distance from B. There are now two other stars brighter than magnitude 10 that are closer to Mu Cassiopeiae, although they are also background objects. The companions C and D are separated from each-other by four

arc second A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of a degree. Since one degree is of a turn, or complete rotation, one arcminute is of a tu ...

s and form a binary system about away. Mu Cassiopeiae itself is known as an

astrometric binary A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...

, a star that is observed to oscillate due to the gravitational influence of an unseen companion, and that companion has now been resolved. In 1961, the close binary nature of this system was discovered by Nicholas E. Wagman at the

Allegheny Observatory The Allegheny Observatory is an American astronomical research institution, a part of the Department of Physics and Astronomy at the University of Pittsburgh. The facility is listed on the National Register of Historic Places (ref. # 79002157, a ...

. Since then the orbital elements of the two stars have been fairly well established. The two stars are separated by a

semimajor axis In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the long ...

of 7.61 AUs with distance range of 3.3-11.9 AUs. In 1966, the individual components were first resolved by the American astronomer Peter A. Wehinger using the 84-inch reflector at the

Kitt Peak National Observatory The Kitt Peak National Observatory (KPNO) is a United States astronomy, astronomical observatory located on Kitt Peak of the Quinlan Mountains in the Arizona-Sonoran Desert on the Tohono Oʼodham Nation, west-southwest of Tucson, Arizona. With ...

, allowing an initial estimate of separate masses. The companion is over six magnitudes (330 times) fainter than the primary star, and it is presumed to be a

red dwarf A red dwarf is the smallest kind of star on the main sequence. Red dwarfs are by far the most common type of fusing star in the Milky Way, at least in the neighborhood of the Sun. However, due to their low luminosity, individual red dwarfs are ...

, a class M main sequence or subdwarf star.

References

External links

*
SolStation entry
{{Stars of Cassiopeia G-type main-sequence stars G-type subdwarfs M-type main-sequence stars Cassiopeiae, Mu Binary stars Cassiopeia (constellation) Cassiopeiae, Mu BD+54 0223 Cassiopeiae, 30 006582 0053 005336 0321

Companions

See also

References

External links