Fomalhaut

Coordinates: Sky map 22h 57m 39.1s, −29° 37′ 20″
Source: Wikipedia, the free encyclopedia.

Fomalhaut

DSS image of Fomalhaut, field of view 2.7×2.9 degrees.
Credit NASA, ESA, and the Digitized Sky Survey 2. Acknowledgment: Davide De Martin (ESA/Hubble)
Observation data
Epoch J2000      Equinox J2000
Constellation Piscis Austrinus (Fomalhaut A+B), Aquarius (Fomalhaut C)
Pronunciation
 /ˈfoʊməl.hɔːt/,[1] /foʊməlˈhɔːt/
Fomalhaut
Right ascension 22h 57m 39.0465s[2]
Declination −29° 37′ 20.050″[2]
Apparent magnitude (V) 1.16[3]
TW Piscis Austrini
Right ascension 22h 56m 24.05256s[4]
Declination −31° 33′ 56.0306″[4]
Apparent magnitude (V) 6.48[5]
LP 876-10
Right ascension 22h 48m 04.47s[6]
Declination −24° 22′ 07.5″[6]
Apparent magnitude (V) 12.618[6]
Characteristics
Spectral type A3 V / K5Vp / M4V[6][7]
U−B color index 0.08 / 1.02 / ?[8]
B−V color index 0.09 / 1.10 / 1.683[6][8]
Variable type None / BY Draconis / ?
Distance
24.793 ± 0.005 ly
(7.602 ± 0.002 pc)
Absolute magnitude (MV)7.08[9]
Details
Fomalhaut
Rotational velocity (v sin i)
2.71[5] km/s
Age4.4 × 108[9] years
NLTT 54872, GSC 06964-01226, 2MASS
J22480446-2422075
Database references
Exoplanet Archive
data
ARICNSA (Fomalhaut)
B (TW PsA)
Fomalhaut A, B are located in the constellation Piscis Austrinus; Fomalhaut C is located in the constellation Aquarius.
A
A
B
B
C
C
Location of Fomalhaut A, B, C

Fomalhaut (

spectrum of this star has served as one of the stable anchor points by which other stars are classified.[17]

It is classified as a

LP 876-10 constitute a triple system, even though the companions are separated by approximately 8 degrees.[21][22]

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.[23][24][19]

Nomenclature

Fomalhaut is the brightest star in the constellation of Piscis Austrinus (center).

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 put it in Aquarius, as well as 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.[25] 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.[26]

The star's traditional name derives from Fom al-Haut from scientific Arabic فم الحوت fam al-ḥūt (al-janūbī) "the mouth of the [Southern] Fish" (literally, "mouth of the whale"), a translation of how Ptolemy labeled it.[27][28] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[29] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[30] 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

Semitic deity, often represented as half-man, half-fish.[35]

Fomalhaut A

Dust ring around Fomalhaut from the Atacama Large Millimeter/submillimeter Array (ALMA)[36]

At a

Square of Pegasus points to it. Continuing the line from Beta to Alpha Pegasi towards the southern horizon, Fomalhaut is about 45˚[clarification needed] south of Alpha Pegasi, with no bright stars in between.[37]

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.[38][39] A 2012 study gave a slightly higher age of 440±40 million years.[9] The surface temperature of the star is around 8,590 K (8,320 °C). 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.[9]

Fomalhaut is slightly

spectroscopic study measured a value equal to 93% of the Sun's abundance of iron.[11][nb 1] 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.[9][40] In 2004, a stellar evolutionary model of Fomalhaut yielded a metallicity of 79%.[10] Finally, in 2008, a spectroscopic measurement gave a significantly lower value of 46%.[12]

Fomalhaut has been claimed to be one of approximately 16 stars belonging to the

moving group has an estimated age of 200±100 million years and originated from the same location.[38] 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.[21] Hence, "membership" in this dynamical group has no bearing on the age of the Fomalhaut system.[21]

Debris disks and suspected planets

See also: Fomalhaut b
Atacama Large Millimeter/submillimeter Array
(ALMA).
debris disk around the star
Debris ring around Fomalhaut showing location of Fomalhaut b—imaged by Hubble Space Telescope's coronagraph.
(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.[20]

The outermost disk is at a radial distance of 133 

protoplanetary,[45] 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.[46]

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.[47] Observations of this outer dust ring by the Atacama Large Millimeter Array also suggested the possible existence of two planets in the system.[48] If there are additional planets from 4 to 10 AU, they must be under 20 MJ; if from 2.5 outward, then 20 MJ.[49]

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.[50][51] 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,[52] and Spitzer Space Telescope imaging suggested that the object Fomalhaut b was more likely to be a dust cloud.[53] 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.[23] Further 2022 observations with the James Webb Space Telescope in mid-infrared failed to resolve the object in the 25.5 μm MIRI wideband filter wavelength range, reported by the same team to be consistent with the previous result.[19]

The same 2022 JWST imaging data discovered another apparent feature in the outer disk, dubbed the “Great Dust Cloud”.[19] However, another team's analysis, which included other existing data, preferred its interpretation as a coincident background object, not part of the outer ring.[54] 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.[55]

The Fomalhaut planetary system[20][23][56]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
Inner hot disk 0.08–0.11 AU — —
Outer hot disk 0.21–0.62 AU or 0.88–1.08 AU — —
10 AU belt 8–12 AU — —
Interbelt dust disk 35–133 AU — —
Main belt 133–158 AU −66.1° —
Main belt outer halo 158–209 AU — —

Fomalhaut B (TW Piscis Austrini)

Main article: TW Piscis Austrini

Fomalhaut forms a binary star with the

K4-type star TW Piscis Austrini (TW PsA), which lies 0.28 parsecs (0.91 light-years) away from Fomalhaut, and its space velocity agrees with that of Fomalhaut within 0.1±0.5 km/s, consistent with being a bound companion. A recent age estimate for TW PsA (400±70 million years) agrees very well with the isochronal age for Fomalhaut (450±40 million years), further arguing for the two stars forming a physical binary.[9]

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 1.2+0.7
−0.6 Jupiter masses, and a poorly defined orbital period with an estimate loosely centering around 25 years.[57]

Fomalhaut C (LP 876-10)

Main article: Fomalhaut C

LP 876-10 is also associated with the Fomalhaut system, making it a

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 0.77 parsecs (2.5 light-years), and it is currently located 0.987 parsecs (3.22 light-years) away from TW PsA (Fomalhaut B). LP 876-10 is located well within the tidal radius of the Fomalhaut system, which is 1.9 parsecs (6.2 light-years).[21] 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.[21] 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.[58]

Etymology and cultural significance

Fomalhaut has had various names ascribed to it through time, and has been recognized by many cultures of the

Eleusis.[59]

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.[63]

Eye of Sauron", comparing its shape and debris ring to the aforementioned "eye" in the Peter Jackson Lord of the Rings films.[64]

USS Fomalhaut (AK-22) was a United States navy amphibious cargo ship.[65]

See also

Notes

  1. ^ Calculation of metallicity: if m = [Fe/H], then the ratio of iron to hydrogen for Fomalhaut divided by the ratio of iron to hydrogen for the Sun is given by 10m.

References

  1. ^ "Fomalhaut". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
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External links

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