Mimosa is the second-brightest object in the southern

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 ...

Crux CRUX is a lightweight x86-64 Linux distribution targeted at experienced Linux users and delivered by a tar.gz-based package system with BSD-style initscripts. It is not based on any other Linux distribution. It also utilizes a ports system ...

(after Acrux), and the 20th-brightest star in the

night sky The night sky is the nighttime appearance of celestial objects like stars, planets, and the Moon, which are visible in a clear sky between sunset and sunrise, when the Sun is below the horizon. Natural light sources in a night sky include moonlig ...

. It has the

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...

β Crucis, which is Latinised to Beta Crucis and abbreviated Beta Cru or β Cru. Mimosa forms part of the prominent asterism called the

Southern Cross CRUX is a lightweight x86-64 Linux distribution targeted at experienced Linux users and delivered by a tar.gz-based package system with BSD-style initscripts. It is not based on any other Linux distribution. It also utilizes a ports system to ...

. It 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 ...

or a possible triple

star system A star system or stellar system is a small number of stars that orbit each other, bound by gravity, gravitational attraction. It may sometimes be used to refer to a single star. A large group of stars bound by gravitation is generally calle ...

Nomenclature

''β Crucis'' (Latinised to ''Beta Crucis'') is the system's

. Although Mimosa is at roughly −60°

declination In astronomy, declination (abbreviated dec; symbol ''δ'') is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. The declination angle is measured north (positive) or ...

, and therefore not visible north of 30°

latitude In geography, latitude is a geographic coordinate system, geographic coordinate that specifies the north-south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from −90° at t ...

, in the time of the

ancient Greeks Ancient Greece () was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity (), that comprised a loose collection of culturally and linguistically re ...

and Romans it was visible north of 40° due to the precession of equinoxes, and these civilizations regarded it as part of the constellation of

Centaurus Centaurus () is a bright constellation in the southern sky. One of the 88 modern constellations by area, largest constellations, Centaurus was included among the 48 constellations listed by the 2nd-century astronomer Ptolemy, and it remains one ...

. It bore the traditional names ''Mimosa'' and the historical name ''Becrux'' . ''Mimosa'', which is derived from the

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

for 'actor', may come from the flower of the same name. ''Becrux'' is a modern contraction of the Bayer designation. In 2016, the

International Astronomical Union The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...

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 proper names for stars for the international astronomical community. It operates under Division C – Education ...

(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 ''Mimosa'' for this star. In Chinese, (), meaning ''

Cross A cross is a religious symbol consisting of two Intersection (set theory), intersecting Line (geometry), lines, usually perpendicular to each other. The lines usually run vertically and horizontally. A cross of oblique lines, in the shape of t ...

'', refers to an asterism consisting of Acrux, Mimosa, Gamma Crucis, and Delta Crucis. Consequently, Mimosa itself is known as (, .).

Stellar system

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 ...

measurements, Mimosa is located at a distance of from the

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

. In 1957, German astronomer Wulff-Dieter Heintz discovered that it is a

spectroscopic 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 ...

with components that are too close together to resolve with a

telescope A telescope is a device used to observe distant objects by their emission, Absorption (electromagnetic radiation), absorption, or Reflection (physics), reflection of electromagnetic radiation. Originally, it was an optical instrument using len ...

. The pair orbit each other every 5 years with an estimated separation that varies from 5.4 to 12.0

Astronomical Unit The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its m ...

s. The system is only 8 to 11 million years old. The primary, β Crucis A, has a

stellar classification In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction gratin ...

of B0.5 III, classifying it as a blue giant that exausted the

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

supply at its

core Core or cores may refer to: Science and technology * Core (anatomy), everything except the appendages * Core (laboratory), a highly specialized shared research resource * Core (manufacturing), used in casting and molding * Core (optical fiber ...

. Asteroseismic observations have measured its mass to be 15 times the

Sun's mass The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies a ...

, its radius to be between 7.3 and 8.9 times the

Sun's radius Solar radius is a unit of distance used to express the size of objects 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_ = 6.957\ti ...

and its age to be 11 million yearsit is the most massive star with an age derived by this method. Mimosa has sufficient mass to explode as a

supernova A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...

, which might occur in roughly 6 million years. The

projected rotational velocity Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface. The rotation of a star produces an equatorial bu ...

of this star is about . However, the orbital plane of the pair is only about 10°, which probably means the inclination of the star's pole is also likely to be low. This suggests that the

azimuth An azimuth (; from ) is the horizontal angle from a cardinal direction, most commonly north, in a local or observer-centric spherical coordinate system. Mathematically, the relative position vector from an observer ( origin) to a point ...

al rotational velocity is quite high, at about . This star has an orbital period of only about 3.6 days. BetaCruLightCurve

β Crucis A is a known

β Cephei variable Beta (, ; uppercase , lowercase , or cursive ; or ) is the second letter of the Greek alphabet. In the system of Greek numerals, it has a value of 2. In Ancient Greek, beta represented the voiced bilabial plosive . In Modern Greek, it represe ...

, although with 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 about 27,000 K it is at the hot edge of the instability strip where such stars are found. It has three different pulsation modes, none of which are

radial Radial is a geometric term of location which may refer to: Mathematics and Direction * Vector (geometric), a line * Radius, adjective form of * Radial distance (geometry), a directional coordinate in a polar coordinate system * Radial set * A ...

. The periods of all three modes are in the range of 4.03–4.59 hours. The high temperature of the star's outer envelope is what gives the star the blue-white hue that is characteristic of B-type stars. It is generating a strong stellar wind and is losing about per year, or the equivalent of the mass of the Sun every 100 million years. The wind is leaving the system with a velocity of 2,000 km s⁻¹ or more. The secondary, β Crucis B, may be a main sequence star with a stellar class of B2. In 2007, a third companion was announced, which may be a low mass, pre-

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 X-ray emission from this star was detected using the

Chandra X-ray Observatory The Chandra X-ray Observatory (CXO), previously known as the Advanced X-ray Astrophysics Facility (AXAF), is a Flagship-class space telescope launched aboard the during STS-93 by NASA on July 23, 1999. Chandra is sensitive to X-ray sources ...

. Two other stars, located at angular separations of 44 and 370

arcseconds 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 ...

, are likely optical companions that are not physically associated with the system. The β Crucis system may be a member of the Lower Centaurus–Crux sub-group of the Scorpius–Centaurus association. This is a

stellar association A stellar association is a very loose star cluster, looser than both open clusters and globular clusters. Stellar associations will normally contain from 10 to 100 or more visible stars. An association is primarily identified by commonalities in i ...

of stars that share a common origin.

In culture

Mimosa is represented in the flags of

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

Samoa Samoa, officially the Independent State of Samoa and known until 1997 as Western Samoa, is an island country in Polynesia, part of Oceania, in the South Pacific Ocean. It consists of two main islands (Savai'i and Upolu), two smaller, inhabited ...

and

Papua New Guinea Papua New Guinea, officially the Independent State of Papua New Guinea, is an island country in Oceania that comprises the eastern half of the island of New Guinea and offshore islands in Melanesia, a region of the southwestern Pacific Ocean n ...

as one of five stars making up the

. It is also featured in the flag of

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

, along with 26 other stars, each of which represents a state. Mimosa represents the State of

Rio de Janeiro Rio de Janeiro, or simply Rio, is the capital of the Rio de Janeiro (state), state of Rio de Janeiro. It is the List of cities in Brazil by population, second-most-populous city in Brazil (after São Paulo) and the Largest cities in the America ...

. A vessel named ''MV Becrux'' is used to export live cattle from Australia to customers in Asia. An episode dedicated to the vessel features in the television documentary series '' Mighty Ships''.

References

External links

* http://jumk.de/astronomie/big-stars/becrux.shtml {{DEFAULTSORT:Mimosa (star) B-type main-sequence stars B-type giants Beta Cephei variables Spectroscopic binaries Lower Centaurus Crux Crux Crucis, Beta 4843 Durchmusterung objects 111123 062434 Stars with proper names