Delta Crucis or δ Crucis, also identified as Imai (), is a

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

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 ...

, and is the faintest of the four bright stars that form the prominent asterism known as the Southern Cross. This star has an

apparent magnitude Apparent magnitude () is a measure of the Irradiance, 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 (astronomy), ...

of 2.8, and its proper name was adopted by 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 ...

on 10 August 2018. Imai is a massive, hot and rapidly rotating star that is in the process of

evolving Evolution is the change in the heritable characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, resulting in certai ...

into a giant, and is located at a distance of about from the Sun.

Nomenclature

''δ Crucis'' ( Latinised to ''Delta Crucis'') is the star's

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 ...

. The International Astronomical Union

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) approved the name ''Imai'' for this star on 10 August 2018 and it is in the list of IAU-approved star names. ''Imai'' is the name selected for the star designated Delta Crucis by the

Mursi people The Mursi (or Mun as they refer to themselves) are a Surmic languages, Surmic ethnic group in Ethiopia. They principally reside in the Debub Omo Zone of the South Ethiopia Regional State, close to the border with South Sudan. According to the 200 ...

of modern-day Ethiopia. The star Imai has some significance as when it "ceases to appear in the evening sky at dusk (around the end of August), it is said that the

Omo River The Omo River (; also called Omo-Bottego) in southern Ethiopia is the largest Ethiopian river outside the Nile Basin. Its course is entirely contained within the boundaries of Ethiopia, and it empties into Lake Turkana on the border with Kenya. T ...

rises high enough to flatten the ''imai'' grass that grows along its banks, and then subsides." The Mursi use a series of southern stars to mark their calendar to track seasonal flooding of the Omo River. It is sometimes called ''Pálida'' (Pale ne in Portuguese.

Properties

This star 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 B2 IV, making it a

subgiant A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution ...

star that is in the process of

away from the

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 ...

and becoming a

red giant A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The stellar atmosphere, outer atmosphere is inflated and tenuous, making the radius large and the surface t ...

. Presently it is radiating around 8,100 times the luminosity of the Sun 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 20,400 K, causing it to glow with a blue-white hue. Delta Crucis is a strong candidate

Beta Cephei variable Beta Cephei variables, also known as Beta Canis Majoris stars, are variable stars that exhibit small rapid variations in their brightness due to pulsations of the stars' surfaces, thought due to the unusual properties of iron at temperatures of 200 ...

. Its rotation is very fast, with a

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 . Delta Crucis is a member of the Lower Centaurus Crux (LCC) component of the

Scorpius–Centaurus association The Scorpius–Centaurus association (sometimes called Sco–Cen or Sco OB2) is the nearest OB association to the Sun. This stellar association is composed of three subgroups (Upper Scorpius, Upper Centaurus–Lupus, and Lower Centaurus–Crux) ...

, which is an

OB association The Ob (; ) is a major river in Russia. It is in western Siberia, and with its tributary the Irtysh forms the world's seventh-longest river system, at . The Ob forms at the confluence of the Biya and Katun which have their origins in the Al ...

of massive stars that share a common origin and motion through space. This is the nearest OB association to the Sun, with the LCC component having an age in the range of 16–20 million years.

In culture

Chinese Chinese may refer to: * Something related to China * Chinese people, people identified with China, through nationality, citizenship, and/or ethnicity **Han Chinese, East Asian ethnic group native to China. **'' Zhonghua minzu'', the supra-ethnic ...

, (), 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 δ Crucis,

γ Crucis Gacrux is the third-brightest star in the southern constellation of Crux, the Southern Cross. It has the Bayer designation Gamma Crucis, which is Latinised from γ Crucis and abbreviated Gamma Cru or γ Cru. With an apparent visual magn ...

α Crucis Acrux is the brightest star in the southern constellation of Crux. It has the Bayer designation α Crucis, which is Latinisation of names, Latinised to Alpha Crucis and abbreviated Alpha Cru or α Cru. With a combined visual magnitude o ...

and

β Crucis Mimosa is the second-brightest object in the southern constellation of Crux (after Acrux), and the 20th-brightest star in the night sky. It has the Bayer designation β Crucis, which is Latinised to Beta Crucis and abbreviated Beta Cr ...

. Consequently, δ Crucis itself is known as (, ). The Aranda and

Luritja The Luritja or Loritja people, also known as Kukatja or Kukatja-Luritja, are an Aboriginal Australian people of the Northern Territory. Their traditional lands are immediately west of the Derwent River, that forms a frontier with the Arrernte p ...

people around

Hermannsburg Hermannsburg is a village and a former municipality in the Celle (district), Celle district, in Lower Saxony, Germany. Since 1 January 2015 it is part of the municipality Südheide (municipality), Südheide. It has been a state-recognised resort t ...

Central Australia Central Australia, also sometimes referred to as the Red Centre, is an inexactly defined region associated with the geographic centre of Australia. In its narrowest sense it describes a region that is limited to the town of Alice Springs and ...

named Iritjinga, "The Eagle-hawk", a quadrangular arrangement comprising this star,

γ Cru Gacrux is the third-brightest star in the southern constellation of Crux, the Southern Cross. It has the Bayer designation Gamma Crucis, which is Latinised from γ Crucis and abbreviated Gamma Cru or γ Cru. With an apparent visual magni ...

(Gacrux),

γ Cen Gamma Centauri is a binary star system in the Southern celestial hemisphere, southern constellation of Centaurus, which is probably part of a wider system together with Tau Centauri. The system is visible to the naked eye as a single po ...

(Muhilfain) and δ Cen (Ma Wei). δ Cru 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 the stars comprising 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 also featured in the

flag of Brazil The national flag of Brazil is a blue disc depicting a starry sky (which includes the Crux, Southern Cross) spanned by a curved band inscribed with the List of national mottos, national motto ('Order and Progress'), within a yellow rhombus, on ...

, along with 26 other stars, each of which represents a state. δ Cru represents the state of

Minas Gerais Minas Gerais () is one of the 27 federative units of Brazil, being the fourth largest state by area and the second largest in number of inhabitants with a population of 20,539,989 according to the 2022 Brazilian census, 2022 census. Located in ...

Notes

References

External links

DELTA CRU
{{Authority control B-type subgiants Beta Cephei variables Lower Centaurus Crux Crux Crucis, Delta Durchmusterung objects 106490 059747 4656

Imai Imai ( — characters for "now" and "water well", meaning "new place of residence") is a Japanese surname. ''The Japanese characters link to the Japanese-language Wikipedia'' *, Japanese animator *, voice actress *, artist and politician *, Japan ...