Sigma Draconis is a single

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 northern

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the earliest constellation ...

Draco Draco is the Latin word for serpent or dragon. Draco or Drako may also refer to: People * Draco (lawgiver) (from Greek: Δράκων; 7th century BC), the first lawgiver of ancient Athens, Greece, from whom the term ''draconian'' is derived * ...

. It has the proper name Alsafi , while Sigma Draconis, which is latinised from σ Draconis and abbreviated Sig Dra or σ Dra, is the

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 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 4.7, which is bright enough to be faintly visible to the naked eye. Based on

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

measurements, this star is located at a distance of 18.8

light year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s 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 radi ...

. It is receding from the Sun with a

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the rate of change of the distance or range between the two points. It is equivalent to the vector projection ...

of 26.8 km/s.

Name

''σ Draconis'' ( Latinised to ''Sigma Draconis'') is the star's

, established in 1603 as part of the ''

Uranometria ''Uranometria'' is a star atlas produced by Johann Bayer. It was published in Augsburg in 1603 by Christoph Mangle (''Christophorus Mangus'') under the full title ''Uranometria: omnium asterismorum continens schemata, nova methodo delineata, a ...

'', a star catalogue produced by German celestial cartographer

Johann Bayer Johann Bayer (1572 – 7 March 1625) was a German lawyer and uranographer (celestial cartographer). He was born in Rain, Lower Bavaria, in 1572. At twenty, in 1592 he began his study of philosophy and law at the University of Ingolstadt, ...

. It bore the traditional name ''Alsafi'', derived from the

Arabic Arabic (, ' ; , ' or ) is a 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. E.Watson; Walter ...

''Athāfi'', itself erroneously transcribed from the Arabic plural ''Athāfiyy'', by which the nomads designated the tripods of their open-air kitchens. It was the name of an association of this star, Tau Draconis and Upsilon Draconis. According to a 1971

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...

memorandum, ''Athāfi'' or ''Alsafi'' were the title for three stars: Sigma Draconis as ''Alsafi'', Tau Draconis as ''Athāfi I'' and Upsilon Draconis as ''Athāfi II''. In 2016, the IAU 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 approved the name ''Alsafi'' for Sigma Draconis on 30 June 2017 and it is now so included in the List of IAU-approved Star Names. In Chinese, (), meaning '' Celestial Kitchen'', refers to an asterism consisting of Sigma Draconis,

Delta Draconis Delta Draconis (δ Draconis, abbreviated Delta Dra, δ Dra), formally named Altais , is a yellow star in the constellation of Draco. It has an apparent visual magnitude of 3.0, making it easily visible to the naked eye. Based on paralla ...

, Epsilon Draconis, Rho Draconis, 64 Draconis (see 64 Draconis (Portuguese)) and

Pi Draconis Pi Draconis, Latinized from π Draconis, is a solitary star in the northern circumpolar constellation of Draco. It is visible to the naked eye with an apparent visual magnitude of 4.59. Based upon an annual parallax shift of 14.25 m ...

. 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 ofte ...

for Sigma Draconis itself is (, en, the Second Star of Celestial Kitchen.)

Properties

Sigma Draconis is a

main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar He ...

dwarf which has long served as a K0 V spectral standard star. Its

classification Classification is a process related to categorization, the process in which ideas and objects are recognized, differentiated and understood. Classification is the grouping of related facts into classes. It may also refer to: Business, organizat ...

as K0 V defines one of the anchor points of the Morgan–Keenan system that have remained unchanged since the original 1943 MKK Atlas. However, some modern spectroscopy gives it as designation of G9 V. The radius of Sigma Draconis has been directly measured using interferometry with the

CHARA array The CHARA (Center for High Angular Resolution Astronomy) array is an optical interferometer, located on Mount Wilson, California. The array consists of six telescopes operating as an astronomical interferometer. Construction was completed in 20 ...

, which yields a result of 77.6% of the Sun's radius. It has 85% of the

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

, but the

luminosity Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a st ...

of this star is only 41% that of the Sun. The projected

rotation rate Rotational frequency (also known as rotational speed or rate of rotation) of an object rotating around an axis is the frequency of rotation of the object. Its unit is revolution per minute (rpm), cycle per second (cps), etc. The symbol for ...

(''v'' sin ''i'') is relatively low at 1.4 km/s. It is considered a slightly

metal-poor In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astronomers use the word ''"metals"'' as ...

star, meaning that it has a lower proportion of elements with masses greater than

helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic ta ...

when compared to the Sun. The temperature, luminosity and surface activity appear to vary slightly in a manner very similar to the

sunspot cycle The solar cycle, also known as the solar magnetic activity cycle, sunspot cycle, or Schwabe cycle, is a nearly periodic 11-year change in the Sun's activity measured in terms of variations in the number of observed sunspots on the Sun's surfac ...

, with a changing duration of 5 to 7 years. The total variability is among the lowest of all stars that have been measured by the

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial ob ...

spacecraft. Sigma Draconis has a high

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 distan ...

, advancing across the

celestial sphere In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth. All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphe ...

at a rate of 1.835

arc seconds 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 n ...

per year. The star made its

perihelion An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any elli ...

passage about 46,725 years ago, when it came within . The components of Sigma Draconis's space velocity are U=+36, V=+40 and W=-10 km/s. This gives the star an unusually large

orbital eccentricity In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values bet ...

about 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 eye. ...

galaxy of 0.30 (compared to 0.06 for the Sun.) The mean galactocentric distance for the orbit is 10.3 kiloparsecs (about 34,000

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distance, astronomical distances and is equivalent to about 9.46 Orders of magnitude (numbers)#1012, trillion kilometers (), or 5.88 ...

s). As of 2013, no Jupiter-size or larger companion had been detected about the star and there was no indication of excess infrared radiation that would be evidence of circumstellar matter (such as 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 di ...

Planet search

Between 2004 and 2013, extensive

measurements were gathered on Sigma Draconis using the High Resolution Echelle Spectrometer on the

Keck Observatory The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. Both telescopes have aperture primary mirrors, and when ...

. The Keck/HIRES data indicated a possible

period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

of about 300 days and a likely

alias Alias may refer to: * Pseudonym * Pen name * Nickname Arts and entertainment Film and television * ''Alias'' (2013 film), a 2013 Canadian documentary film * ''Alias'' (TV series), an American action thriller series 2001–2006 * ''Alias the J ...

period of 2800 days. Adding data taken with the

Automated Planet Finder The Automated Planet Finder (APF) Telescope a.k.a. Rocky Planet Finder, is a fully robotic 2.4-meter optical telescope at Lick Observatory, situated on the summit of Mount Hamilton, east of San Jose, California, USA.Steven S. Vogt et al., APF - T ...

at the

Lick Observatory The Lick Observatory is an astronomical observatory owned and operated by the University of California. It is on the summit of Mount Hamilton, in the Diablo Range just east of San Jose, California, United States. The observatory is managed by t ...

strengthened and narrowed the 300-day period while reducing the significance of the 2800-day period. The combined analysis suggests there may be a

Uranus Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus ( Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars), grandfather of Zeus (Jupiter) and father of ...

-mass planet on a 308-day orbit, though the authors do not yet consider the discovery to be publishable as they have not yet attempted to rule out other non-planetary explanations for the velocity variations.

Notes

References

External links

* {{DEFAULTSORT:Sigma Draconis K-type main-sequence stars Draco (constellation) Draconis, Sigma 7462 BD+69 1053 Draconis, 61 0764 185144 096100 Alsafi