Fomalhaut
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 Debris ring around Fomalhaut showing location of planet Fomalhaut b—imaged by Hubble Space Telescope's coronagraph. NASA photo. |
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| Observation data Epoch J2000 Equinox J2000 |
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|---|---|
| Constellation | Piscis Austrinus |
| Pronunciation | /ˈfoʊməlhɔːt/ |
| Right ascension | 22h 57m 39.1s |
| Declination | -29° 37′ 20″ |
| Apparent magnitude (V) | 1.16 |
| Characteristics | |
| Spectral type | A3 V |
| U-B color index | 0.08 |
| B-V color index | 0.09 |
| Astrometry | |
| Radial velocity (Rv) | +6.5 km/s |
| Proper motion (μ) | RA: 329.22 mas/yr Dec.: −164.22 mas/yr |
| Parallax (π) | 130.58 ± 0.65 mas |
| Distance | 25 ± 0.1 ly (7.66 ± 0.04 pc) |
| Absolute magnitude (MV) | 1.73 |
| Details | |
| Mass | 2.1 ± 0.2[1] M☉ |
| Radius | 1.832[1] R☉ |
| Surface gravity (log g) | 4.21[1] |
| Luminosity | 17.66[1] L☉ |
| Temperature | 8,751[1] K |
| Metallicity | [Fe/H] = −0.10[1] |
| Rotational velocity (v sin i) | 93[1] km/s |
| Age | (2 ± 1) × 108[1] years |
| Other designations | |
| Database references | |
| SIMBAD | data |
| ARICNS | data |
| Extrasolar Planets Encyclopaedia |
data |
Fomalhaut (α PsA / α Piscis Austrini / Alpha Piscis Austrini) is the brightest star in the constellation Piscis Austrinus and one of the brightest stars in the sky. Fomalhaut can be seen low in the southern sky in the northern hemisphere in fall and early winter evenings. Near latitude 50˚N, it sets around the time Sirius rises, and does not reappear until Antares sets. Its name means "mouth of the whale", from the Arabic فم الحوت fum al-ḥawt. It is a class A star on the main sequence approximately 25 light-years (7.7 pc) from Earth. It is classified as a Vega-like star that emits excess infrared radiation, indicating it is surrounded by a circumstellar disk.
Fomalhaut holds a special significance in extrasolar planet research, as it is the center of the first stellar system with an extrasolar planet (Fomalhaut b) imaged at visible wavelengths. The image was published in Science in November 2008.[2]
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[edit] Properties
Fomalhaut is believed to be a young star, only 100 to 300 million years old, with a potential lifespan of a billion years.[citation needed] The surface temperature of the star is around 8,751 K (15,292 °F; 8,478 °C). Compared to the Sun, its mass is about 2.1, its luminosity is about 18, and its diameter is roughly 1.8. Fomalhaut has a slightly lower proportion of elements with higher atomic numbers than helium: about 79% as much as the Sun.[1][note 1]
Fomalhaut is a member of the 16 stars belonging to the Castor Moving Group. This is an association of stars that shares a common motion through space and are therefore likely to be physically associated. Other members of this group include Castor and Vega. This moving group has an estimated age of 200 ± 100 million years and originated from the same location.[3] The nearby star TW Piscis Austrini, a member of this group, may form a physical pair with Fomalhaut.[4]
[edit] System
Fomalhaut is surrounded by a debris disk of dust in a toroidal shape with a very sharp inner edge at a radial distance of 133 AU (1.99×1010 km; 1.24×1010 mi), inclined 24 degrees from edge-on.[5][6] The dust is distributed in a belt about 25 AU wide. The geometric center of the disk is offset by about 15 AU (2.2×109 km; 1.4×109 mi) from Fomalhaut.[7] The disk is sometimes referred to as "Fomalhaut's Kuiper belt". Fomalhaut's dusty disk is believed to be protoplanetary,[8] 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.[9]
On November 13, 2008, astronomers announced the discovery of an extrasolar planet orbiting just inside the debris ring. This was the first extrasolar planet to be seen with visible light, captured by the Hubble Space Telescope.[10][11] The planet's existence had been previously suspected from the sharp, elliptical inner edge of Fomalhaut's debris disk.[12] The mass of the planet, Fomalhaut b, is estimated to be no more than three times the mass of Jupiter and at least the mass of Neptune. There are indications that the planet's orbit is not apsidally-aligned with the dust disk, which may indicate that additional planets may be responsible for the dust disk's structure.[13] However M-band images taken from the MMT Observatory put strong limits on the existence of gas giants within 40 AU of the star.[14]
The much-fainter flare star TW Piscis Austrini is located within a light year of Fomalhaut and the two share a common proper motion through the sky. They are believed to be companion stars and may have had a common origin in a star cluster.
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (years) |
Eccentricity |
|---|---|---|---|---|
| b | 0.054 - 3.0 MJ | ~115 | ~872 | ~0.11 |
| Dust disk | 133 — 158 AU | |||
[edit] Etymology and cultural significance
Fomalhaut has had various names ascribed to it through time. One such name in common use is the Lonely Star of Autumn, because it is the only first-magnitude star in the autumn sky of mid-northern latitudes. It has been recognized by many cultures of the northern hemisphere, including the Arabs, Persians and Chinese. Archaeological evidence links it to rituals dating back to about 2500 BC. It is one of the Persians' four "royal stars".
- The name Fom al-Haut comes from scientific Arabic فم الحوت fam al-ħūt (al-janūbī) "the mouth of the (southern) fish/whale"
- The Latin names are ōs piscis merīdiāni, ōs piscis merīdionālis, ōs piscis notii "the mouth of the southern fish"
- The name Difda al Auwel comes from the colloquial Arabic الضفدع الأول aḍ-ḍifdiˤ al-’awwal "the first frog" (the second frog is Beta Ceti)
[edit] See also
[edit] Notes
- ^ As [Fe/H] = -0.10, the ratio of iron to hydrogen is given by 10-0.10 = 0.79
[edit] References
- ^ a b c d e f g h i Di Folco, E.; Thévenin, F.; Kervella, P.; Domiciano de Souza, A.; Coudé du Foresto, V.; Ségransan, D.; Morel, P. (2004). "VLTI near-IR interferometric observations of Vega-like stars". Astronomy and Astrophysics 426: 601−617. doi:.
- ^ Kalas, Paul; et al. (2008). "Optical Images of an Exosolar Planet 25 Light-Years from Earth". Science 322 (5906): 1345–1348. doi:.
- ^ Barrado y Navascués, D. (1998). "The Castor Moving Group: The age of Fomalhaut and Vega". Astronomy and Astrophysics 339: 831–839. http://arxiv.org/abs/astro-ph/9905243. Retrieved on 2008-11-17.
- ^ Barrado y Navascués, David; Stauffer, John R.; Hartmann, Lee; Balachandran, Suchitra C. (1997-01-20). "The Age of Gliese 879 and Fomalhaut". The Astrophysical Journal 475: 313–321. doi:.
- ^ Kalas, Paul; Graham, James R.; Clampin, Mark (2005). "A planetary system as the origin of structure in Fomalhaut's dust belt". Nature 435 (7045): 1067–1070. doi:. arΧiv:astro-ph/0506574.
- ^ The disc was reported by Holland, Wayne S.; et al. (1998). "Submillimetre images of dusty debris around nearby stars". Nature 392 (6678): 788–791. doi:. They noted that the disc was centered on a cavity, which they suggested might have been swept out by planets.
- ^ "Fomalhaut's Kuiper Belt". Sky & Telescope. http://www.skyandtelescope.com/news/3310401.html?page=1&c=y. Retrieved on October 16 2007.
- ^ "Hubble Directly Observes a Planet Orbiting Another Star". http://www.nasa.gov/mission_pages/hubble/science/fomalhaut.html. Retrieved on November 13 2008.
- ^ Le Bouquin, Jean-Baptiste et al. (2009). "The spin-orbit alignment of the Fomalhaut planetary system probed by optical long baseline interferometry". arΧiv: 0904.1688 [astro-ph].
- ^ "From afar, the first optical photos of an exoplanet". AFP. 2008-11-13. http://afp.google.com/article/ALeqM5iA-PPiKC8oJh3qqkV2ZsF09HmmCA.
- ^ a b Paul Kalas (2008-11-13). "Direct Image Of Extrasolar Planet". http://uk.youtube.com/watch?v=aXKz4nxyPqw. Retrieved on 2008-11-14. (at 3 minutes 45 seconds: "... has to be less than three Jupiter masses. In fact our lower limit to Fomalhaut b is Neptune")
- ^ Predictions for a planet just inside Fomalhaut's eccentric ring, Alice C. Quillen, Monthly Notices of the Royal Astronomical Society, 372, #1 (October 2006), pp. L14–L18, doi:10.1111/j.1745-3933.2006.00216.x, Bibcode: 2006MNRAS.372L..14Q.
- ^ Chiang, E. et al. (2008). "Fomalhaut's Debris Disk and Planet: Constraining the Mass of Fomalhaut b From Disk Morphology". arΧiv: 0811.1985v1 [astro-ph].
- ^ Kenworthy, Matthew A. et al. (2008). "MMT/AO 5 micron Imaging Constraints on the Existence of Giant Planets Orbiting Fomalhaut at ~13-40 AU". arΧiv: 0811.2443v1 [astro-ph].
[edit] External links
- "Fomalhaut". SolStation. http://www.solstation.com/stars/fomalhau.htm. Retrieved on November 23 2005.
- Preprint of planet discovery paper
