Omicron Ursae Majoris (ο Ursae Majoris, abbreviated Omicron UMa, ο UMa), formally named Muscida , is a

star system A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a '' star cluster'' or ''galaxy'', although, broadly speakin ...

in the northern

circumpolar constellation A circumpolar star is a star that, as viewed from a given latitude on Earth, never sets below the horizon due to its apparent proximity to one of the celestial poles. Circumpolar stars are therefore visible from said location toward the nearest po ...

Ursa Major Ursa Major (; also known as the Great Bear) is a constellation in the northern sky, whose associated mythology likely dates back into prehistory. Its Latin name means "greater (or larger) bear," referring to and contrasting it with nearby Ursa ...

. It has an

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's lig ...

of +3.35 and is located at a distance of around from the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared rad ...

. In 2012, an extrasolar planet, designated Omicron Ursae Majoris Ab was found to be orbiting the primary.

Nomenclature

''ο Ursae Majoris'' ( Latinised to ''Omicron Ursae Majoris'') is the star's

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars. T ...

. The traditional name ''Muscida'' was shared with the optical

double star In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes. This occurs because the pair either forms a binary star (i.e. a ...

Pi Ursae Majoris The Bayer designation Pi Ursae Majoris (π UMa, π Ursae Majoris) is shared by two stars in the constellation Ursa Major: * Pi¹ Ursae Majoris (3 Ursae Majoris) * Pi² Ursae Majoris (4 Ursae Majoris) They are separated by 0.70° in the sky. ...

. In 2016, the

International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach ...

organized a

Working Group on Star Names The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize List of proper names of stars, proper names for stars for the international astronomical community. It operates under ...

(WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included ''Muscida'' for this star. In

Chinese Chinese can refer to: * Something related to China * Chinese people, people of Chinese nationality, citizenship, and/or ethnicity **''Zhonghua minzu'', the supra-ethnic concept of the Chinese nation ** List of ethnic groups in China, people of v ...

, (), meaning '' Inner Steps'', refers to an asterism consisting of ο Ursae Majoris,

16 Ursae Majoris c Ursae Majoris is the Bayer designation for a double-lined spectroscopic binary star system in the northern constellation of Ursa Major. It has an apparent visual magnitude of 5.18, which indicates that is visible to the naked eye. Par ...

6 Ursae Majoris 6 (six) is the natural number following 5 and preceding 7. It is a composite number and the smallest perfect number. In mathematics Six is the smallest positive integer which is neither a square number nor a prime number; it is the second small ...

23 Ursae Majoris 23 Ursae Majoris, or 23 UMa, is a binary star system in the constellation Ursa Major, located is approximately 77.7 light years from the Sun. It has the Bayer designation h Ursae Majoris; ''23 Ursae Majoris'' is the Flamsteed designatio ...

, 5 Ursae Majoris and 17 Ursae Majoris. Consequently, the

Chinese name Chinese names or Chinese personal names are names used by individuals from Greater China and other parts of the Chinese-speaking world throughout East and Southeast Asia (ESEA). In addition, many names used in Japan, Korea and Vietnam are oft ...

for ο Ursae Majoris itself is (, en, the First Star of Inner Steps.).

Properties and observations

The

stellar classification 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 t ...

of this star, G4 II–III, places it midway between the

giant In folklore, giants (from Ancient Greek: '' gigas'', cognate giga-) are beings of human-like appearance, but are at times prodigious in size and strength or bear an otherwise notable appearance. The word ''giant'' is first attested in 1297 fr ...

and

bright giant A giant star is a star with substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature.Giant star, entry in ''Astronomy Encyclopedia'', ed. Patrick Moore, New York: Oxford University Press, ...

stages of its

evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

. The

interferometry Interferometry is a technique which uses the '' interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber o ...

-measured

angular diameter The angular diameter, angular size, apparent diameter, or apparent size is an angular distance describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the visual angle, and in optics, it i ...

of this star is about 2.42

mas Mas, Más or MAS may refer to: Film and TV * Más y Menos, fictional superhero characters, from the Teen Titans animated television series * "Más" (''Breaking Bad''), a season three episode of ''Breaking Bad'' Songs * ''Más'' (album), by Span ...

, which, at its estimated distance, equates to a physical radius of about 14 times the

radius of the Sun Solar radius is a unit of distance used to express the size of stars in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: :1\,R_ = 6.9 ...

. It has about three times the mass of the Sun and radiates 138 times the Sun's luminosity from its outer atmosphere at an

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of 5,282 K, giving it the yellowish hue of a G-type star. In 1963, East German astronomer Gerhard Jakisch reported this star as a

variable Variable may refer to: * Variable (computer science), a symbolic name associated with a value and whose associated value may be changed * Variable (mathematics), a symbol that represents a quantity in a mathematical expression, as used in many ...

with a period of 358 days and an amplitude of 0.08 magnitude. The 1982 edition of the ''

New Catalogue of Suspected Variable Stars The ''New Catalogue of Suspected Variable Stars'' (NSV) is a star catalogue A star catalogue is an astronomical catalogue that lists stars. In astronomy, many stars are referred to simply by catalogue numbers. There are a great many different ...

'' listed it with a variability from 3.30 to 3.36 in the visual band. However, in 1992 American astronomer

Dorrit Hoffleit Ellen Dorrit Hoffleit (March 12, 1907 – April 9, 2007) was an American senior research astronomer at Yale University. She is best known for her work in variable stars, astrometry, spectroscopy, meteors, and the Bright Star Catalog. She is a ...

noted that the two comparison stars used to determine the variability may themselves be variable. Hence the actual variability of this star may be suspect. Muscida has a magnitude 15.2

common proper motion This glossary of astronomy is a list of definitions of terms and concepts relevant to astronomy and cosmology, their sub-disciplines, and related fields. Astronomy is concerned with the study of celestial objects and phenomena that originate outsi ...

companion at an

angular separation Angular distance \theta (also known as angular separation, apparent distance, or apparent separation) is the angle between the two sightlines, or between two point objects as viewed from an observer. Angular distance appears in mathematics (in pa ...

of 7.1

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

s. With a probability of 99.4%, this companion is the source for the X-ray emission from the system. Omicron Ursae Majoris is sometimes listed with two more companions, but, based on

proper motion Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...

data, these appear to be optical companions. No other companions were detected by 2016. This system is a member of the

thin disk population This glossary of astronomy is a list of definitions of terms and concepts relevant to astronomy and cosmology, their sub-disciplines, and related fields. Astronomy is concerned with the study of celestial objects and phenomena that originate outsi ...

and is following an orbit through the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked ey ...

galaxy with an

eccentricity Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off- center, in geometry * Eccentricity (graph theory) of a ...

of 0.12. It comes as close to the

Galactic Center The Galactic Center or Galactic Centre is the rotational center, the barycenter, of the Milky Way galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a compact ...

as and as distant as . This orbit carries it no more than about 330 ly (100 pc) above the

galactic plane The galactic plane is the plane on which the majority of a disk-shaped galaxy's mass lies. The directions perpendicular to the galactic plane point to the galactic poles. In actual usage, the terms ''galactic plane'' and ''galactic poles'' usual ...

. It is considered a

runaway star In astronomy, stellar kinematics is the observational study or measurement of the kinematics or motions of stars through space. Stellar kinematics encompasses the measurement of stellar velocities in the Milky Way and its satellites as well as t ...

because it has a high

peculiar velocity Peculiar motion or peculiar velocity refers to the velocity of an object relative to a '' rest frame'' — usually a frame in which the average velocity of some objects is zero. Galactic astronomy In galactic astronomy, peculiar motion refers ...

of 35.5 km s⁻¹ relative to the typical motion of stars in its vicinity. The star has no detectable magnetic fields.

Planetary system

In 2012, an extrasolar planet designated Omicron Ursae Majoris b and orbiting the primary at 3.9 astronomical units, was found. This gas giant (4.1 times as massive as Jupiter) completes an orbit in 1630 days.

References

{{Stars of Ursa Major G-type giants Planetary systems with one confirmed planet Binary stars Runaway stars Ursa Major (constellation) Ursae Majoris, Omicron Durchmusterung objects Ursae Majoris, 01 041704 071369 3323 Muscida J08301592+6043056