Alpha Fornacis (α Fornacis, abbreviated Alpha For, α For) is 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 ...

system 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 ...

Fornax Fornax () is a constellation in the southern celestial hemisphere, partly ringed by the celestial river Eridanus (constellation), Eridanus. Its name is Latin for furnace. It was named by French astronomer Nicolas Louis de Lacaille in 1756. Forna ...

. It is the brightest star in the constellation and the only one brighter than magnitude 4.0. Based on

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

measurements obtained during the

Gaia mission ''Gaia'' was a space observatory of the European Space Agency (ESA) that was launched in 2013 and operated until March 2025. The spacecraft was designed for astrometry: measuring the positions, distances and motions of stars with unprecedented ...

, it is 45.66

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 distant. Its three components are designated Alpha Fornacis A (officially named Dalim ), Alpha Fornacis Ba and Alpha Fornacis Bb.

Nomenclature

''α Fornacis'' ( Latinised to ''Alpha Fornacis'') 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 components as ''Alpha Fornacis A, Ba and Bb'' derive from the convention used by the Washington Multiplicity Catalog (WMC) for

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

, 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). Formerly it was designated as the 12th of Eridanus (12 Eri) by Flamsteed. Indigenous Arabs had named both Alpha Eridani and Fomalhaut ظَلِيم ''al-ẓalīm'', a local word for 'ostrich'. Later, Arabian astronomer would transfer the appellation to

Theta Eridani Theta Eridani, Romanization of Greek, Latinized from θ Eridani, is a binary star, binary system in the constellation of Eridanus (constellation), Eridanus with a combined apparent magnitude of 2.88. Its two components are designated θ1 ...

, as they could not see those other stars from their location. In recent times, Italian astronomer

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 ...

applied it with the spelling ''Dalim'' to his "III 13" (= α For) in his '' Palermo Catalogue'', and Elijah Burritt labeled it ''Fornacis'' in his

Atlas An atlas is a collection of maps; it is typically a bundle of world map, maps of Earth or of a continent or region of Earth. Advances in astronomy have also resulted in atlases of the celestial sphere or of other planets. Atlases have traditio ...

. plate III. 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 decided to attribute proper names to individual stars rather than entire multiple systems. It approved the name ''Dalim'' for the component Alpha Fornacis A on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.

Properties

Alpha Fornacis has a high

proper motion Proper motion is the astrometric measure of changes in the apparent places of stars or other celestial objects as they move relative to the center of mass of the Solar System. It is measured relative to the distant stars or a stable referenc ...

and the system displays an excess of infrared emission, which may indicate the presence of circumstellar material 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 ...

. The space velocity components of this star are (U, V, W) = (−35, +20, +30) km/s. Approximately 350,000 years ago, Alpha Fornacis experienced a close encounter with the

A-type main-sequence star An A-type main-sequence star (A) or A dwarf star is a main-sequence (hydrogen burning) star of spectral type A and luminosity class (five). These stars have spectra defined by strong hydrogen Balmer absorption lines. They measure between 1 ...

Nu Horologii Nu Horologii, Latinized from ν Horologii, is the Bayer designation for a single star in the southern constellation of Horologium. It was catalogued by the Dutch explorer Frederick de Houtman in 1603. With an apparent visual magnitude o ...

. The two came within an estimated of each other, and both stars have debris disks. Alpha Fornacis A 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 F6V, where the luminosity class V suggests this is a

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 ...

star. It is a fairly old star which has sometimes been considered to be 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 ...

, although evolutionary models place it towards the end of its main sequence life. It has 33% more mass than the Sun and is an estimated 2.9 billion years old. The secondary, Alpha Fornacis B, has been identified as a

blue straggler A blue straggler is a type of star that is more luminous and bluer than expected. Typically identified in a stellar cluster, they have a higher effective temperature than the main sequence turnoff point for the cluster, where ordinary stars b ...

, and has likely accumulated material from a third star in the past. It is a strong source of X-rays and is 78% as massive as the Sun. Such a third star, designated Alpha Fornacis Bb, was detected in 2016. Alpha Fornacis Ba is enriched in

barium Barium is a chemical element; it has symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element. Th ...

relative to star A, suggesting that its companion is likely a

white dwarf A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...

References

External links

α For (Dalim)
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SKY-MAP.ORG

LHL Digital Collections
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Linda Hall library
{{DEFAULTSORT:Alpha Fornacis F-type main-sequence stars Fornacis, Alpha Blue stragglers Triple star systems Fornax Fornacis, Alpha CD−29 1177 Circumstellar disks Eridani, 12 0127 020010 014879 0127 Dalim J03120443-2859156 G-type main-sequence stars White dwarfs