Alpha Delphini (α Delphini, abbreviated Alpha Del, α Del) is a

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 ...

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 ...

Delphinus Delphinus is a small constellation in the Northern Celestial Hemisphere, close to the celestial equator. Its name is the Latin version for the Greek word for dolphin (). It is one of the 48 constellations listed by the 2nd-century astronomer Pt ...

. It consists of a

triple star 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 ''sta ...

, designated Alpha Delphini A, together with five faint, probably

optical Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultravio ...

companions, designated Alpha Delphini B, C, D, E and F. A's two components are themselves designated Alpha Delphini Aa (officially named Sualocin , the historical name for the entire system) and Ab.

Nomenclature

''α Delphini'' ( Latinised to ''Alpha Delphini'') 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 six constituents as ''Alpha Delphini A'' to ''F'', and those of ''A's'' components - ''Alpha Delphini Aa'' and ''Ab'' - derive from the convention used by the Washington Multiplicity Catalog (WMC) for

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 primary star's components Aa, Ab1, and Ab2 are also sometimes referred to as A, Ba, and Bb respectively, given that the outer pair have been resolved. The system bore an historical name, ''Sualocin'', which arose as follows:

Niccolò Cacciatore Niccolò Cacciatore (; 26 January 1770 – 28 January 1841) was an Italian astronomer. Cacciatore was born at Casteltermini, in Sicily. While studying mathematics and physics in Palermo, he became acquainted with Giuseppe Piazzi, head of the Pale ...

was the assistant to

Giuseppe Piazzi Giuseppe Piazzi ( , ; 16 July 1746 – 22 July 1826) was an Italian Catholic Church, Catholic priest of the Theatines, Theatine order, mathematician, and astronomer. He established an observatory at Palermo, now the ''Palermo Astronomical Ob ...

, and later his successor as Director of the Palermo Observatory. The name first appeared in Piazzi's Palermo Star Catalogue. When the Catalogue was published in 1814, the unfamiliar names ''Sualocin'' and ''Rotanev'' were attached to ''Alpha'' and ''

Beta Delphini Beta Delphini (β Delphini, abbreviated Beta Del, β Del) is a binary star in the constellation of Delphinus. It is the brightest star in Delphinus. The two components of the system are designated Beta Delphini ...

'', respectively. Eventually the Reverend Thomas Webb, a British astronomer, puzzled out the explanation. Cacciatore's name, ''Nicholas Hunter'' in English translation, would be Latinised to ''Nicolaus Venator''. Reversing the letters of this construction produces the two-star names. They have endured, the result of Cacciatore's little practical joke of naming the two stars after himself. 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 ''Sualocin'' for the component Alpha Delphini Aa on 12 September 2016, and it is now so included in the List of IAU-approved Star Names. In Chinese, (), meaning '' Good Gourd'', refers to an asterism consisting of Alpha Delphini, Gamma² Delphini,

Delta Delphini Delta Delphini, Latinized from δ Delphini, is a binary star in the northern constellation of Delphinus. It is visible to the naked eye with an apparent visual magnitude of 4.43. Based upon an annual parallax shift of 14.61 mas as ...

, Beta Delphini and

Zeta Delphini Zeta Delphini (ζ Delphini) is a star in the constellation of Delphinus. With an apparent magnitude of about 4.6, it is faintly visible to the naked eye. Parallax measurements of the system made by the Hipparcos spacecraft put it at a dis ...

. Consequently, the

Chinese name 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-ethni ...

for Alpha Delphini itself is (, ). In

Hindu astronomy Astronomy has a long history in the Indian subcontinent, stretching from pre-historic to modern times. Some of the earliest roots of Indian astronomy can be dated to the period of Indus Valley civilisation or earlier. Astronomy later develope ...

, the star corresponded to one of the

nakshatra Nakshatra () is the term for Lunar mansion in Hindu astrology and Buddhist astrology. A nakshatra is one of 27 (sometimes also 28) sectors along the ecliptic. Their names are related to a prominent star or asterisms in or near the respective s ...

s named Dhanishta.

Properties

Alpha Delphini A 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 ...

star which has now been resolved using

speckle interferometry Speckle imaging comprises a range of high-resolution Astrophotography, astronomical imaging techniques based on the analysis of large numbers of short Exposure (photography), exposures that freeze the variation of Astronomical seeing, atmospheri ...

. The components are separated by and have a 17-year

orbit In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an ...

. Alpha Delphini Aa has a

spectral type In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

of B9IV. It is 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 ...

that has begun to evolve 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 ...

, is about 3.8 times as massive as the sun and about twice as hot. The spectral type of the secondary star cannot be determined as it is too close and too faint compared to the primary, but it has been shown to itself be a binary star with an orbit of 30 days. Spectral lines showing 30-day

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 ...

changes are likely to belong to the faintest component, expected from its mass to be an F-type star. Then the more massive star of the inner pair is likely to be an A-type dwarf, possibly not detected in the spectral because rapid rotation blurs its

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. The five faint companions have

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 ...

s around 11th to 13th magnitude and separations of 35" to 72". They all show motion relative to Alpha Delphini A, and have much smaller parallaxes.

References

{{DEFAULTSORT:Alpha Delphini Delphini, Alpha Delphini, 09 Delphinus Binary stars 7 B-type subgiants Sualocin 101958 7906 BD+15 4222 196867