Fomalhaut
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Fomalhaut (Template:IPAc-en, Template:IPAc-en<ref>Template:Cite LPD</ref>) is the brightest star in the southern constellation of Piscis Austrinus, the Southern Fish, and one of the brightest stars in the night sky. It has the Bayer designation Alpha Piscis Austrini, which is an alternative form of α Piscis Austrini, and is abbreviated Alpha PsA or α PsA. This is a class A star on the main sequence approximately Template:Convert from the Sun as measured by the Hipparcos astrometry satellite.<ref name=GSM/> Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.<ref name=baas25_1319/>
It is classified as a Vega-like star that emits excess infrared radiation,<ref name="NYT-20230508">Template:Cite news</ref><ref name="Gaspar2023"/> indicating it is surrounded by a circumstellar disk.<ref name=vegalikedisc/> Fomalhaut, K-type main-sequence star TW Piscis Austrini, and M-type, red dwarf star LP 876-10 constitute a triple system, even though the companions are separated by approximately 8 degrees.<ref name=Mamajek2013/><ref name=skyandtelescope2014-10-01/>
Fomalhaut was the first stellar system with an extrasolar planet candidate imaged at visible wavelengths, designated Fomalhaut b. However, analyses in 2019 and 2023 of existing and new observations indicate that Fomalhaut b is not a planet, but rather an expanding region of debris from a massive planetesimal collision.<ref name="gaspar20newhst"/><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="Gaspar2023"/>
NomenclatureEdit
α Piscis Austrini, or Alpha Piscis Austrini, is the system's Bayer designation. It also bears the Flamsteed designation of 24 Piscis Austrini. The classical astronomer Ptolemy included it in the constellation of Aquarius, along with the rest of Piscis Austrinus. In the 17th century, Johann Bayer firmly planted it in the primary position of Piscis Austrinus. Following Ptolemy, John Flamsteed in 1725 additionally denoted it 79 Aquarii. The current designation reflects modern consensus on Bayer's decision, that the star belongs in Piscis Austrinus.<ref>Template:Cite journal</ref> Under the rules for naming objects in multiple-star systems, the three components – Fomalhaut, TW Piscis Austrini and LP 876-10 – are designated A, B and C, respectively.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
The star's traditional name derives from Fom al-Haut from scientific Arabic {{#invoke:Lang|lang}} Template:Transliteration "the mouth of the [Southern] Fish" (literally, "mouth of the whale"), a translation of how Ptolemy labeled it.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name=rhallen/><ref> Template:Cite book </ref> Fam in Arabic means "mouth", al "the", and ḥūt "fish"<ref> فم الحوت </ref> or "whale".<ref> حوت </ref> In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)<ref name="WGSN">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016<ref name="WGSN1">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> included a table of the first two batches of names approved by the WGSN, which included the name "Fomalhaut" for this star.
In July 2014, the International Astronomical Union (IAU) launched NameExoWorlds, a process for giving proper names to certain exoplanets.<ref>NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars. IAU.org. 9 July 2014</ref> The process involved public nomination and voting for the new names.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> In December 2015, the IAU announced "Dagon" as the winning name for Fomalhaut b.<ref>Final Results of NameExoWorlds Public Vote Released, International Astronomical Union, 15 December 2015.</ref> The winning name was proposed by Todd Vaccaro and forwarded by the St. Cloud State University Planetarium of St. Cloud, Minnesota, United States of America, to the IAU for consideration.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Dagon was a Semitic deity, often represented as half-man, half-fish.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }} </ref>
ObservationEdit
At a declination of −29.6°, Fomalhaut is located south of the celestial equator, and hence is best viewed from the Southern Hemisphere. However, its southerly declination is not as great as that of stars such as Acrux, Alpha Centauri and Canopus, meaning that, unlike them, Fomalhaut is visible from a large part of the Northern Hemisphere as well, being best seen in autumn. Its declination is greater than that of Sirius and similar to that of Antares. At 40°N, Fomalhaut rises above the horizon for eight hours and reaches only 20° above the horizon, while Capella, which rises at approximately the same time, will stay above the horizon for twenty hours. Fomalhaut can be located in northern latitudes by the fact that the western (right-hand) side of the Square of Pegasus points to it. Continuing the line from Beta to Alpha Pegasi towards the southern horizon, Fomalhaut is about 45˚Template:Clarify south of Alpha Pegasi, with no bright stars in between.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Fomalhaut AEdit
Fomalhaut is a young star, for many years thought to be only 100 to 300 million years old, with a potential lifespan of a billion years.<ref name="age"/><ref name="lifespan"/> A 2012 study gave a slightly higher age of Template:Val.<ref name="age_mam"/> The surface temperature of the star is around Template:Convert. Fomalhaut's mass is about 1.92 times that of the Sun, its luminosity is about 16.6 times greater, and its diameter is roughly 1.84 times as large.<ref name="age_mam"/>
Fomalhaut is slightly metal-deficient compared to the Sun, which means it is composed of a smaller percentage of elements other than hydrogen and helium.<ref name="aaa426" /> The metallicity is typically determined by measuring the abundance of iron in the photosphere relative to the abundance of hydrogen. A 1997 spectroscopic study measured a value equal to 93% of the Sun's abundance of iron.<ref name=mnras286_3/><ref name=metal group=nb/> A second 1997 study deduced a value of 78%, by assuming Fomalhaut has the same metallicity as the neighboring star TW Piscis Austrini, which has since been argued to be a physical companion.<ref name="age_mam"/><ref name=apj475/> In 2004, a stellar evolutionary model of Fomalhaut yielded a metallicity of 79%.<ref name=aaa426/> Finally, in 2008, a spectroscopic measurement gave a significantly lower value of 46%.<ref name=aaa490_1/>
Fomalhaut has been claimed to be one of approximately 16 stars belonging to the Castor Moving Group. This is an association of stars which share a common motion through space, and have been claimed to be physically associated. Other members of this group include Castor and Vega. The moving group has an estimated age of Template:Val and originated from the same location.<ref name="age"/> More recent work has found that purported members of the Castor Moving Group appear to not only have a wide range of ages, but their velocities are too different to have been possibly associated with one another in the distant past.<ref name=Mamajek2013/> Hence, "membership" in this dynamical group has no bearing on the age of the Fomalhaut system.<ref name=Mamajek2013/>
Debris disks and suspected planetsEdit
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(January 8, 2013; North is up, East left) (NASA).
Fomalhaut is surrounded by several debris disks.
The inner disk is a high-carbon small-grain (10–300 nm) ash disk, clustering at 0.1 AU from the star. Next is a disk of larger particles, with inner edge 0.4-1 AU of the star. The innermost disk is unexplained as yet.<ref name=vegalikedisc>Template:Cite journal</ref>
The outermost disk is at a radial distance of Template:Convert, in a toroidal shape with a very sharp inner edge, all inclined 24 degrees from edge-on.<ref name=nature435_7045_1067/><ref name=nature392_6678_788/> The dust is distributed in a belt about 25 AU wide. The geometric center of the disk is offset by about Template:Convert from Fomalhaut.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The disk is sometimes referred to as "Fomalhaut's Kuiper belt". Fomalhaut's dusty disk is believed to be protoplanetary,<ref name="nasaprot">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and emits considerable infrared radiation. Measurements of Fomalhaut's rotation indicate that the disk is located in the star's equatorial plane, as expected from theories of star and planet formation.<ref>Template:Cite journal</ref>
Herschel Space Observatory images of Fomalhaut, analysed in 2012, reveal that a large amount of fluffy micrometer-sized dust is present in the outer dust belt. Because such dust is expected to be blown out of the system by stellar radiation pressure on short timescales, its presence indicates a constant replenishment by collisions of planetesimals. The fluffy morphology of the grains suggests a cometary origin. The collision rate is estimated to be approximately 2000 kilometre-sized comets per day.<ref>Template:Cite journal</ref> Observations of this outer dust ring by the Atacama Large Millimeter Array also suggested the possible existence of two planets in the system.<ref>Template:Cite journal</ref> If there are additional planets from 4 to 10 AU, they must be under Template:Jupiter mass; if from 2.5 outward, then Template:Jupiter mass.<ref>Template:Cite journal</ref>
On November 13, 2008, astronomers announced an extrasolar planet candidate, orbiting just inside the outer debris ring. This was the first extrasolar orbiting object candidate to be directly imaged in visible light, captured by the Hubble Space Telescope.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="Kalas2008"/> The mass of the tentative planet, Fomalhaut b, was estimated to be less than three times the mass of Jupiter, and at least the mass of Neptune. However, M-band images taken from the MMT Observatory put strong limits on the existence of gas giants within 40 AU of the star,<ref>Template:Cite journal</ref> and Spitzer Space Telescope imaging suggested that the object Fomalhaut b was more likely to be a dust cloud.<ref>Template:Cite journal</ref> A later 2019 synthesis of new and existing direct observations of the object confirmed that it is expanding, losing brightness, has not enough mass to detectably perturb the outer ring while crossing it, and is probably a dispersing cloud of debris from a massive planetesimal collision on a hyperbolic orbit destined to leave the Fomalhaut A system.<ref name="gaspar20newhst"/> Further 2022 observations with the James Webb Space Telescope in mid-infrared failed to resolve the object in the Template:Val MIRI wideband filter wavelength range, reported by the same team to be consistent with the previous result.<ref name="Gaspar2023"/>
The same 2022 JWST imaging data discovered another apparent feature in the outer disk, dubbed the "Great Dust Cloud".<ref name="Gaspar2023"/> However, another team's analysis, which included other existing data, preferred its interpretation as a coincident background object, not part of the outer ring.<ref name="Kennedy2023"/> Another 2023 study detected 10 point sources around Fomalhaut; all but one of these are background objects, including the "Great Dust Cloud", but the nature of the last is unclear. It may be a background object, or a planetary companion to Fomalhaut.<ref name="Ygouf2023"/>
Template:OrbitboxPlanet begin Template:OrbitboxPlanet disk |- | Outer hot disk | colspan="4"| 0.21–0.62 AU or 0.88–1.08 AU | — | — Template:OrbitboxPlanet disk Template:OrbitboxPlanet disk Template:OrbitboxPlanet disk Template:OrbitboxPlanet disk Template:Orbitbox end
Fomalhaut B (TW Piscis Austrini)Edit
{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}} Fomalhaut forms a binary star with the K4-type star TW Piscis Austrini (TW PsA), which lies Template:Convert away from Fomalhaut, and its space velocity agrees with that of Fomalhaut within Template:Val, consistent with being a bound companion. A recent age estimate for TW PsA (Template:Val) agrees very well with the isochronal age for Fomalhaut (Template:Val), further arguing for the two stars forming a physical binary.<ref name="age_mam"/>
The designation TW Piscis Austrini is astronomical nomenclature for a variable star. Fomalhaut B is a flare star of the type known as a BY Draconis variable. It varies slightly in apparent magnitude, ranging from 6.44 to 6.49 over a 10.3 day period. While smaller than the Sun, it is relatively large for a flare star. Most flare stars are red M-type dwarfs.
In 2019, a team of researchers analyzing the astrometry, radial velocity measurements, and images of Fomalhaut B suggested the existence of a planet orbiting the star with a mass of Template:Val Jupiter masses, and a poorly defined orbital period with an estimate loosely centering around 25 years.<ref name=AstronomicalJournal2019-10-07>Template:Cite journal</ref>
Fomalhaut C (LP 876-10)Edit
{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}} LP 876-10 is also associated with the Fomalhaut system, making it a trinary star. In October 2013, Eric Mamajek and collaborators from the RECONS consortium announced that the previously known high-proper-motion star LP 876-10 had a distance, velocity, and color-magnitude position consistent with being another member of the Fomalhaut system.<ref name="Mamajek2013" /> LP 876-10 was originally catalogued as a high-proper-motion star by Willem Luyten in his 1979 NLTT catalogue; however, a precise trigonometric parallax and radial velocity was only measured quite recently. LP 876-10 is a red dwarf of spectral type M4V, and located even farther from Fomalhaut A than TW PsA—about 5.7° away from Fomalhaut A in the sky, in the neighbouring constellation Aquarius, whereas both Fomalhaut A and TW PsA are located in constellation Piscis Austrinus. Its current separation from Fomalhaut A is about Template:Convert, and it is currently located Template:Convert away from TW PsA (Fomalhaut B). LP 876-10 is located well within the tidal radius of the Fomalhaut system, which is Template:Convert.<ref name="Mamajek2013" /> Although LP 876-10 is itself catalogued as a binary star in the Washington Double Star Catalog (called "WSI 138"), there was no sign of a close-in stellar companion in the imaging, spectral, or astrometric data in the Mamajek et al. study.<ref name="Mamajek2013" /> In December 2013, Kennedy et al. reported the discovery of a cold dusty debris disk associated with Fomalhaut C, using infrared images from the Herschel Space Observatory. Multiple-star systems hosting multiple debris disks are exceedingly rare.<ref name="GMKennedy2013" />
Etymology and cultural significanceEdit
Fomalhaut has had various names ascribed to it through time, and has been recognized by many cultures of the northern hemisphere, including the Arabs, Persians, and Chinese. It marked the solstice in 2500 BC. It was also a marker for the worship of Demeter in Eleusis.Template:Refn
- It is considered to be one of the four "royal stars" of the Persians.<ref name=rhallen>Template:Cite book</ref>
- The Latin names are {{#invoke:Lang|lang}} "the mouth of the Southern Fish".<ref name=rhallen/>
- A folk name among the early Arabs was Difdi' al Awwal ({{#invoke:Lang|lang}} Template:Transliteration) "the first frog" (the second frog is Beta Ceti).<ref name=rhallen/>
- The Chinese name {{#invoke:Lang|lang}} (Mandarin: Běiluòshīmén), meaning North Gate of the Military Camp, because this star is marking itself and stands alone in North Gate of the Military Camp asterism, Encampment mansion (see: Chinese constellations).<ref>{{#invoke:citation/CS1|citation
|CitationClass=web }}</ref> {{#invoke:Lang|lang}} (Běiluòshīmén), westernized into Pi Lo Sze Mun by R.H. Allen.<ref name=rhallen/>
- To the Moporr Aboriginal people of South Australia, it is a male being called Buunjill.<ref>Template:Cite book</ref> The Wardaman people of the Northern Territory called Fomalhaut Menggen —white cockatoo.<ref>Template:Cite book</ref>
Fomalhaut-Earthwork B, in Mounds State Park near Anderson, Indiana, lines up with the rising of the star Fomalhaut in the fall months, according to the Indiana Department of Natural Resources. In 1980, astronomer Jack Robinson proposed that the rising azimuth of Fomalhaut was marked by cairn placements at both the Bighorn medicine wheel in Wyoming, USA, and the Moose Mountain medicine wheel in Saskatchewan, Canada.<ref>Template:Cite journal</ref>
New Scientist magazine termed it the "Great Eye of Sauron", comparing its shape and debris ring to the aforementioned "eye" in the Peter Jackson Lord of the Rings films.<ref>Template:Cite news</ref>
USS Fomalhaut (AK-22) was a United States navy amphibious cargo ship.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
See alsoEdit
- Exoasteroid
- 2M1207
- GJ 758
- HR 8799
- Direct imaging of extrasolar planets
- Lists of exoplanets
- List of star systems within 25–30 light-years
NotesEdit
ReferencesEdit
External linksEdit
- {{#invoke:citation/CS1|citation
|CitationClass=web }}
- Astrobites summary of Boley et al. 2012, the ALMA observations of the Fomalhaut ring system
- "Eye of Sauron" debris ring
- Researchers find that bright nearby double star Fomalhaut is actually a triple (Astronomy magazine : October 8, 2013)
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