Delta Capricorni, or δ Capricorni, 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 ...

located 38.7

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s from the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

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 first constellati ...

Capricornus Capricornus is one of the constellations of the zodiac. Its name is Latin for "horned goat" or "goat Horn (anatomy), horn" or "having horns like a goat's", and it is commonly represented in the form of a sea goat: a mythical creature that is hal ...

(the Sea

Goat The goat or domestic goat (''Capra hircus'') is a species of Caprinae, goat-antelope that is mostly kept as livestock. It was domesticated from the wild goat (''C. aegagrus'') of Southwest Asia and Eastern Europe. The goat is a member of the ...

). The system consists of an

eclipsing binary A binary star or binary star system is a Star system, system of two stars that are gravity, 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 ...

, Delta Capricorni A, and two visual companions that are over 10 magnitudes fainter, labeled B and C. Delta Capricorni A's two components are designated Delta Capricorni Aa (formally named Deneb Algedi , the traditional name of the system) and Ab. The primary star, Aa, is a

white giant A giant star has a substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzspr ...

and the combined light of Aa and Ab makes it the brightest star in the constellation. Delta Capricorni is 2.6 degrees south of the

ecliptic The ecliptic or ecliptic plane is the orbital plane of Earth's orbit, Earth around the Sun. It was a central concept in a number of ancient sciences, providing the framework for key measurements in astronomy, astrology and calendar-making. Fr ...

and can be

occulted An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks f ...

by the

Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

, and (rarely) by

planet A planet is a large, Hydrostatic equilibrium, rounded Astronomical object, astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets b ...

Nomenclature

''δ Capricorni'' ( Latinised to ''Delta Capricorni'') is the system'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 designations of the three constituents as ''Delta Capricorni A'', ''B'' and ''C'', and those of ''A's'' components – ''Delta Capricorni Aa'' and ''Ab'' – derive from the convention used by the Washington Multiplicity Catalog (WMC) for

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

s, and 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 ...

(IAU). The system bore the traditional names ''Deneb Algedi'', derived from the

Arabic Arabic (, , or , ) is a Central Semitic languages, Central Semitic language of the Afroasiatic languages, Afroasiatic language family spoken primarily in the Arab world. The International Organization for Standardization (ISO) assigns lang ...

ذنب الجدي (''ðanab al-jady''), meaning "the tail of the goat", referring to the fishlike tail of the celestial sea-goat Capricorn, and ''Scheddi''. In 2016, the

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 catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems. It approved the name ''Deneb Algedi'' for the component Delta Capricornii Aa on February 1, 2017 and it is now so included in the List of IAU-approved Star Names. In

Chinese astronomy Astronomy in China has a long history stretching from the Shang dynasty, being refined over a period of more than 3,000 years. The Ancient China, ancient Chinese people have identified stars from 1300 BCE, as Chinese star names later categori ...

, Delta Capricorni is known as (), meaning 'The Fourth Star of the Line of Ramparts'. This refers to its presence among an asterism known as ' The Line of Ramparts', which also includes Kappa Capricorni, Epsilon Capricorni, Gamma Capricorni, Iota Aquarii, Lambda Aquarii, Sigma Aquarii, Phi Aquarii,

27 Piscium 27 Piscium is a binary star system in the zodiac constellation of Pisces. It is visible to the naked eye with an apparent visual magnitude of 4.88. Based upon an annual parallax shift of , it is located about 234 light years away. ...

, 29 Piscium, 33 Piscium and 30 Piscium. ''中國星座神話'', written by 陳久金. Published by 台灣書房出版有限公司, 2005, .

Observational history

In 1906 astronomer

Vesto Slipher Vesto Melvin Slipher (; November 11, 1875 – November 8, 1969) was an American astronomer who performed the first measurements of radial velocities for galaxies. He was the first to discover that distant galaxies are redshifted, thus providing ...

Lowell Observatory Lowell Observatory is an astronomical observatory in Flagstaff, Arizona, United States. Lowell Observatory was established in 1894, placing it among the oldest observatories in the United States, and was designated a National Historic Landmark ...

discovered that Delta Capricorni A was 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 ...

. The orbit was determined in 1921 by Clifford Crump using 69

radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity ...

measurements obtained at

Yerkes Observatory Yerkes Observatory ( ) is an astronomical observatory located in Williams Bay, Wisconsin, United States. The observatory was operated by the University of Chicago Department of Astronomy and Astrophysics from its founding in 1897 until 2018. O ...

. However the

nature of the system was not discovered until 1956 by Olin J. Eggen at

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 (California), Mount Hamilton, in the Diablo Range just east of San Jose, California, United States. The ...

. Lunar occultations have been observed in 1951, 1962, and 1988. Delta Capricorni was recognised as a metallic-line star in 1957 and included in a 1958 catalog of magnetic stars. It has also been associated with

extreme ultraviolet Extreme ultraviolet radiation (EUV or XUV) or high-energy ultraviolet radiation is electromagnetic radiation in the part of the electromagnetic spectrum spanning wavelengths shorter than the hydrogen Lyman-alpha line from 121 nm down to ...

and radio sources, believed to be from coronal activity in the secondary star.

Stellar system

Delta Capricorni A is an

Algol ALGOL (; short for "Algorithmic Language") is a family of imperative computer programming languages originally developed in 1958. ALGOL heavily influenced many other languages and was the standard method for algorithm description used by the ...

-type

eclipsing binary star A binary star or binary star system is a Star system, system of two stars that are gravity, 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 ...

, with an

orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...

of 1.022768 days and an

inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Eart ...

close to the line of sight from the Earth. The peak

apparent visual magnitude Apparent magnitude () is a measure of the 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 of the object's light ca ...

of the pair is 2.81. During an eclipse of the primary, this magnitude drops by 0.24. When the primary is eclipsing the secondary, the magnitude decreases by 0.09. Delta Capricorni A has an overall

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 A7m III, indicating that it is a

giant star A giant star has a substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzsp ...

that has exhausted the supply of hydrogen at its core. More specifically, this is a chemically-peculiar

Am star An Am star or metallic-line star is a type of chemically peculiar star of spectral type A whose spectrum has strong and often variable absorption lines of metals such as zinc Zinc is a chemical element; it has symbol Zn and atomic number 30. ...

with a spectral type of kA5hF0mF2 III under the revised MK system. This notation indicates that the calcium K-line matches the temperature of an A5 star, the hydrogen spectral type matches an F0 star, and the metallic

absorption line Absorption spectroscopy is spectroscopy that involves techniques that measure the absorption (electromagnetic radiation), absorption of electromagnetic radiation, as a function of frequency or wavelength, due to its interaction with a sample. Th ...

s match an F2 star. In the past this star was suspected of being a

Delta Scuti variable A Delta Scuti variable (sometimes termed dwarf cepheid when the V-band amplitude is larger than 0.3 mag.) is a class of pulsating star, comprising several sub-classes of object with A- or F-type spectra. The variables follow a period-luminosity ...

, which is rare for an Am star. This categorization was brought into question during observations in 1994 and it is most likely not inherently variable. The primary has double 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 ...

and nearly twice its radius. It is rotating rapidly 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 105 km s⁻¹. (This rotation rate is synchronous with the orbital period.) Note that it is unusual for an Am star to have such a high rotational velocity. The outer envelope of the star is radiating energy 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 7,301 K, giving it the white-hued glow of an A-type star. The secondary component is a G-type or K-type star with around 90% of the mass of the Sun. There are two optical companions. A fifteenth magnitude star is one

arcminute 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 ...

away, and a thirteenth magnitude star is over two arcminutes away from the primary star and that distance is increasing.

In culture

According to

astrology Astrology is a range of Divination, divinatory practices, recognized as pseudoscientific since the 18th century, that propose that information about human affairs and terrestrial events may be discerned by studying the apparent positions ...

, Delta Capricorni's representation of a flexible tail is reflected in its association with both good and bad fortune alike. It was one of the fifteen Behenian stars of

medieval In the history of Europe, the Middle Ages or medieval period lasted approximately from the 5th to the late 15th centuries, similarly to the post-classical period of World history (field), global history. It began with the fall of the West ...

astrology, associated with

chalcedony Chalcedony ( or ) is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monoclinic ...

marjoram Marjoram (, ''Origanum majorana'') is a cold-sensitive perennial plant, perennial herb or undershrub with sweet pine and citrus flavours. In some Middle Eastern countries, marjoram is synonymous with oregano, and there the names sweet marjoram ...

and the

kabbalistic Kabbalah or Qabalah ( ; , ; ) is an esoteric method, discipline and school of thought in Jewish mysticism. It forms the foundation of mystical religious interpretations within Judaism. A traditional Kabbalist is called a Mekubbal (). Jewi ...

symbol .

References

links

* * {{DEFAULTSORT:Delta Capricorni Capricorni, Delta Capricornus Algol variables Eclipsing binaries Spectroscopic binaries Deneb Algedi A-type giants Capricorni, 49 107556 8322 F-type giants 207098 Durchmusterung objects Am stars 0837