Alpha Sagittarii (α Sagittarii, abbreviated Alpha Sgr, α Sgr), also named Rukbat ,
is a
star
A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
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 origins of the e ...
of
Sagittarius.
Properties
Alpha Sagittarii is a blue,
class B dwarf star
A dwarf star is a star of relatively small size and low luminosity. Most main sequence stars are dwarf stars. The meaning of the word "dwarf" was later extended to some star-sized objects that are not stars, and compact stellar remnants which are ...
. It does not appear particularly bright in the sky to the naked eye, with a visual
apparent 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 li ...
of +3.97.
The star has 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 ...
about twice that of 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 radi ...
and is nearly three times as massive, with a luminosity in visible wavelengths about 117 times that of the Sun. Based on an
excess emission of infrared radiation, it may have a
debris disk
A debris disk (American English), or debris disc (Commonwealth English), is a circumstellar disk of dust and debris in orbit around a star. Sometimes these disks contain prominent rings, as seen in the image of Fomalhaut on the right. Debris dis ...
, much like
Vega
Vega is the brightest star in the northern constellation of Lyra. It has the Bayer designation α Lyrae, which is Latinised to Alpha Lyrae and abbreviated Alpha Lyr or α Lyr. This star is relatively close at only from the Sun, an ...
.
It is a single-lined spectroscopic binary system. The ROSAT All Sky Survey discovered that Alpha Sagittarii is emitting an excess flux of X-rays, which is not expected to originate from a star of this spectral class. The most likely explanation is that the companion is an active pre-main sequence star or else a star that has just reached the main sequence.
[
]
Nomenclature
''α Sagittarii'' ( Latinised to ''Alpha Sagittarii'') 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. ...
. It is unclear why Bayer
Bayer AG (, commonly pronounced ; ) is a German multinational corporation, multinational pharmaceutical and biotechnology company and one of the largest pharmaceutical companies in the world. Headquartered in Leverkusen, Bayer's areas of busi ...
designated this star as the alpha
Alpha (uppercase , lowercase ; grc, ἄλφα, ''álpha'', or ell, άλφα, álfa) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of one. Alpha is derived from the Phoenician letter aleph , whic ...
, rather than Epsilon Sagittarii
Epsilon Sagittarii ( Latinised from ε Sagittarii, abbreviated Epsilon Sgr, ε Sgr), formally named Kaus Australis , is a binary star system in the southern zodiac constellation of Sagittarius. The apparent visual magnit ...
or Sigma Sagittarii
Sigma Sagittarii, Latinized from σ Sagittarii; formally named Nunki , is the second-brightest star in the constellation of Sagittarius. It has an apparent magnitude of +2.05, making it readily visible to the naked eye. The distanc ...
. This led some old star charts to occasionally depict Alpha and Beta Sagittarii as much brighter than they are in reality, as they are invisible from northern Europe, being too far south to see there.
The star bore the traditional names ''Rukbat'' and ''Alrami'', derived from the Arabic
Arabic (, ' ; , ' or ) is a Semitic languages, Semitic language spoken primarily across the Arab world.Semitic languages: an international handbook / edited by Stefan Weninger; in collaboration with Geoffrey Khan, Michael P. Streck, Janet C ...
''rukbat al-rāmī'' 'the knee of the archer'. The star Delta Cassiopeiae also bore the traditional names ''Ruchbah'' or ''Rukbat'', from the Arabic word ركبة ''rukbah'' meaning "knee". 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, outreac ...
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)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 ...
, (), meaning '' Celestial Spring'', refers to an asterism consisting of Alpha Sagittarii, Beta¹ Sagittarii and Beta² Sagittarii. 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 often a ...
for Alpha Sagittarii itself is (, en, the Third Star of Celestial Spring.)AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 2 日
/ref>
This star, together with Beta¹ Sagittarii and Beta² Sagittarii, were ''Al Ṣuradain'' (ألسردين), the two Surad, desert birds.
In popular culture
A fictionalized version of the Rukbat system is the setting for Anne McCaffrey
Anne Inez McCaffrey (1 April 1926 – 21 November 2011) was an American-Irish writer known for the ''Dragonriders of Pern'' science fiction series. She was the first woman to win a Hugo Award for fiction (Best Novella, ''Weyr Search'', 19 ...
's Dragonriders of Pern
''Dragonriders of Pern'' is a science fantasy series written primarily by American author Anne McCaffrey, who initiated it in 1967. Beginning in 2003, her middle child Todd McCaffrey has written Pern novels, both solo and jointly with Anne. ...
series of novels. In the canon of this series, the system has five planets in standard orbits, two asteroid belts, an Oort cloud
The Oort cloud (), sometimes called the Öpik–Oort cloud, first described in 1950 by the Dutch astronomer Jan Oort, is a theoretical concept of a cloud of predominantly icy planetesimals proposed to surround the Sun at distances ranging from 2 ...
, and has also captured a rogue planet
A rogue planet (also termed a free-floating planet (FFP), interstellar, nomad, orphan, starless, unbound or wandering planet) is an interstellar object of planetary-mass, therefore smaller than fusors (stars and brown dwarfs) and without a h ...
into a highly eccentric orbit which passes both through the Oort cloud and through the inner solar system on a 250 year orbit.
References
External links
*
{{DEFAULTSORT:Alpha Sagittarii
Sagittarius (constellation)
Sagittarii, Alpha
B-type main-sequence stars
Rukbat
095347
181869
PD-40 08955
7348