Editing Fomalhaut (section)

==Fomalhaut A==
[[File:ALMA observes a ring around the bright star Fomalhaut.jpg|left|thumb|Dust ring around Fomalhaut from the [[Atacama Large Millimeter Array|Atacama Large Millimeter/submillimeter Array]] (ALMA)<ref>{{cite news|title=ALMA Reveals Workings of Nearby Planetary System|url=http://www.eso.org/public/images/eso1216a/|access-date=13 April 2012|newspaper=ESO Press Release}}</ref> ]]

At a [[declination]] of −29.6°, Fomalhaut is located south of the [[Celestial coordinate system|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 (star)|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 Pegasi|Beta]] to [[Alpha Pegasi]] towards the southern horizon, Fomalhaut is about 45˚{{clarify|date=December 2023}} south of Alpha Pegasi, with no bright stars in between.<ref>{{cite web|url=http://www.astronomyhouston.org/newsletters/guidestar/shallow-sky-object-month-fomalhaut|title=Shallow Sky Object of the Month: Fomalhaut|date=August 2013|website=Houston Astronomical Society|access-date=2014-07-30}}</ref>

===Properties===
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 {{val|440|40|u=million years}}.<ref name="age_mam"/> The surface temperature of the star is around {{convert|8590|K|C|lk=on}}. 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 [[metallicity|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 (star)|Castor]] and [[Vega]]. The [[moving group]] has an estimated age of {{val|200|100|u=million years}} 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 planets===
{{See also|Fomalhaut b}}
[[File:Fomalhaut Dusty Debris Disk (MIRI Compass Image).png|thumb|left|Image of the asteroid belt by the [[James Webb Space Telescope]]<ref>{{Cite web |last=Adkins |first=Jamie |date=2023-05-08 |title=Webb Looks for Fomalhaut's Asteroid Belt and Finds Much More |url=http://www.nasa.gov/feature/goddard/2023/webb-looks-for-fomalhaut-s-asteroid-belt-and-finds-much-more |access-date=2023-05-08 |website=NASA}}</ref> with annotations by NASA.]][[File:Fomalhaut annotated.jpg|thumb|left|This image shows the discovery features in the debris disk of Fomalhaut from the  [[James Webb Space Telescope]] (JWST) as well as overlays of [[Hubble Space Telescope]] (HST) data and the [[Atacama Large Millimeter/submillimeter Array]] (ALMA).]]
[[File:Fomalhaut B entire-Hubble Telescope.jpg|thumb|right|The [[Debris ring|debris disk]] around the [[star]]]]
[[File:NASA's Hubble Reveals Rogue Planetary Orbit For Fomalhaut B.jpg|thumb|right|[[Debris ring]] around Fomalhaut showing location of [[Fomalhaut b]]—imaged by [[Hubble Space Telescope]]'s coronagraph.<br />(January 8, 2013; North is up, East left) ([[NASA]]).]]
Fomalhaut is surrounded by several [[debris disk]]s.

The inner disk is a high-carbon small-grain (10–300&nbsp;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>{{cite journal | journal=Astrophysical Journal | volume=763 | issue=2 | page=119 | title=An interferometric study of the Fomalhaut inner debris disk II. Keck Nuller mid-infrared observations |arxiv=1211.7143 |date=2012 |bibcode = 2013ApJ...763..119M |doi = 10.1088/0004-637X/763/2/119 | last1=Mennesson | first1=B. | last2=Absil | first2=O. | last3=Lebreton | first3=J. | last4=Augereau | first4=J.-C. | last5=Serabyn | first5=E. | last6=Colavita | first6=M. M. | last7=Millan-Gabet | first7=R. | last8=Liu | first8=W. | last9=Hinz | first9=P. | last10=Thébault | first10=P. | s2cid=102339596}}</ref>

The outermost disk is at a radial distance of {{convert|133|AU|km mi|lk=in|abbr=on}}, in a [[Toroid (geometry)|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 {{convert|15|AU|km mi|abbr=on}} from Fomalhaut.<ref>{{cite web | title=Fomalhaut's Kuiper Belt | work=Sky & Telescope | url=http://www.skyandtelescope.com/news/3310401.html?page=1&c=y | access-date=October 16, 2007 | date=2005-06-22 | archive-date=2014-03-18 | archive-url=https://web.archive.org/web/20140318123718/http://www.skyandtelescope.com/news/3310401.html?page=1&c=y }}</ref> The disk is sometimes referred to as "Fomalhaut's [[Kuiper belt]]". Fomalhaut's dusty disk is believed to be [[Protoplanetary disc|protoplanetary]],<ref name="nasaprot">{{cite web| title=Hubble Directly Observes a Planet Orbiting Another Star | url=http://www.nasa.gov/mission_pages/hubble/science/fomalhaut.html | access-date=November 13, 2008}}</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>{{Cite journal|title=The spin-orbit alignment of the Fomalhaut planetary system probed by optical long baseline interferometry|journal=Astronomy and Astrophysics|volume=498|issue=3|pages=L41–L44|author=Le Bouquin, Jean-Baptiste|date=2009|arxiv=0904.1688|display-authors=etal|doi=10.1051/0004-6361/200911854|bibcode = 2009A&A...498L..41L |s2cid=17766995}}</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>{{cite journal|title=Herschel images of Fomalhaut. An extrasolar Kuiper belt at the height of its dynamical activity|author=B. Acke |display-authors=etal |arxiv=1204.5037|type=class: astro-ph|date=2012|journal=Astronomy & Astrophysics|volume=540 |pages=A125 |doi = 10.1051/0004-6361/201118581 |bibcode = 2012A&A...540A.125A |s2cid=10506379 }}</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>{{Cite journal|title=Constraining the Planetary System of Fomalhaut Using High-Resolution ALMA Observations|journal=The Astrophysical Journal|volume=750|issue=1|pages=L21|author=Boley, A.|arxiv=1204.0007|type=class: astro-ph|date=2012|display-authors=etal|doi=10.1088/2041-8205/750/1/L21|bibcode = 2012ApJ...750L..21B |s2cid=73622306}}</ref> If there are additional planets from 4 to 10 AU, they must be under {{Jupiter mass|20}}; if from 2.5 outward, then {{Jupiter mass|20}}.<ref>{{cite journal|title=Coronagraphic Observations of Fomalhaut at Solar System Scales|arxiv=1212.1459|type=class: astro-ph|date=2012|journal=Astrophysical Journal|volume=764|issue=1|page=7|bibcode = 2013ApJ...764....7K |doi = 10.1088/0004-637X/764/1/7 |last1=Kenworthy|first1=Matthew A.|last2=Meshkat|first2=Tiffany|last3=Quanz|first3=Sascha P.|last4=Girard|first4=Julien H.|last5=Meyer|first5=Michael R.|last6=Kasper|first6=Markus|s2cid=54214491}}</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>{{cite web |url=http://www.berkeley.edu/news/media/releases/2008/11/13_exoplanet.shtml |title=Hubble snaps first optical photo of exoplanet  |publisher=Berkeley News |date=2008-11-13 | access-date=2017-10-03 }}</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>{{Cite journal|title=MMT/AO 5 micron Imaging Constraints on the Existence of Giant Planets Orbiting Fomalhaut at ~13–40 AU|journal=The Astrophysical Journal|volume=697|issue=2|pages=1928–1933|author=Kenworthy, Matthew A.|arxiv=0811.2443|year=2009|display-authors=etal|doi=10.1088/0004-637X/697/2/1928|bibcode = 2009ApJ...697.1928K |s2cid=119234101}}</ref> and [[Spitzer Space Telescope]] imaging suggested that the object Fomalhaut b was more likely to be a dust cloud.<ref>{{Cite journal|title=Infrared Non-detection of Fomalhaut b—Implications for the Planet Interpretation|journal=The Astrophysical Journal|volume=747|issue=2|page=116|author=Markus, J.|arxiv=1201.4388|date=2012|display-authors=etal|doi=10.1088/0004-637X/747/2/116|bibcode = 2012ApJ...747..116J |s2cid=119256885}}</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&nbsp;A system.<ref name="gaspar20newhst"/> Further 2022 observations with the [[James Webb Space Telescope]] in mid-infrared failed to resolve the object in the {{val|25.5|u=um}} [[Mid-Infrared Instrument#Filters|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"/>

{{OrbitboxPlanet begin
|table_ref = <ref name="vegalikedisc" /><ref name="gaspar20newhst" /><ref name="Kalas2013">{{cite journal|title=STIS Coronagraphic Imaging of Fomalhaut: Main Belt Structure and the Orbit of Fomalhaut b|author1=Kalas, Paul |author2=Graham, James R. |author3=Fitzgerald, Michael P. |author4=Clampin, Mark |date=2013|journal=The Astrophysical Journal|volume=775|issue=1|pages=article id. 56|doi=10.1088/0004-637X/775/1/56|bibcode=2013ApJ...775...56K|arxiv=1305.2222|s2cid=62877509 }}</ref>
}}
{{OrbitboxPlanet disk
| disk = Inner hot disk <!-- centred around 0.1AU (from introduction, first paragraph, of the  Bertrand Mennesson et al. (2013) paper)-->
| periapsis = 0.08
| apoapsis = 0.11
}}
|-
| '''Outer hot disk'''
| colspan="4"| 0.21–0.62 [[Astronomical unit|AU]] ''or'' 0.88–1.08 [[Astronomical unit|AU]]
| —
| —
{{OrbitboxPlanet disk
| disk = 10 AU belt
| periapsis = 8
| apoapsis = 12
}}
{{OrbitboxPlanet disk
| disk = Interbelt dust disk
| periapsis = 35
| apoapsis = 133
}}
{{OrbitboxPlanet disk
| disk = Main belt
| periapsis = 133
| apoapsis = 158
| inclination = −66.1
}}
{{OrbitboxPlanet disk
| disk = Main belt outer halo
| periapsis = 158
| apoapsis = 209
}}
{{Orbitbox end}}