Fomalhaut
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This article is about the star. For the extrasolar planet, see Fomalhaut b.
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)
Fomalhaut
Right ascension
22h 57m 39.0465s[1]
Declination
−29° 37′ 20.050″[1]
Apparent magnitude (V)
1.16
TW Piscis Austrini
Right ascension
22h 56m 24.05327s[1]
Declination
−31° 33′ 56.0351″[1]
Apparent magnitude (V)
6.48[2]
LP 876-10
Right ascension
22h 48m 04.47s[3]
Declination
−24° 22′ 07.5″[3]
Apparent magnitude (V)
12.618[3]
Characteristics
Spectral type
A3 V / K5Vp / M4V[4][3]
U−B color index
0.08 / 1.02 / ?[5]
B−V color index
0.09 / 1.10 / 1.683[5][3]
Variable type
None / BY Draconis / ?
Astrometry
Fomalhaut
Radial velocity (Rv)
+6.5 km/s
Proper motion (μ)
RA: +328.95[1] mas/yr
Dec.: −164.67[1] mas/yr
Parallax (π)
129.81 ± 0.47[1] mas
Distance
25.13 ± 0.09 ly
(7.70 ± 0.03 pc)
Absolute magnitude (MV)
1.72[6]
TW Piscis Austrini
Radial velocity (Rv)
+6[2] km/s
Proper motion (μ)
RA: −331.11[1] mas/yr
Dec.: −158.98[1] mas/yr
Parallax (π)
131.42 ± 0.62[1] mas
Distance
24.82 ± 0.09 ly
(7.61 ± 0.04 pc)
Absolute magnitude (MV)
7.08[6]
Details
Fomalhaut
Mass
1.92±0.02[6] M☉
Radius
1.842±0.019[6] R☉
Luminosity
16.63±0.48[6] L☉
Surface gravity (log g)
4.21[7] cgs
Temperature
8,590[6] K
Metallicity [Fe/H]
−0.03[8] to −0.34[9] dex
Rotational velocity (v sin i)
93[7] km/s
Age
(4.4±0.4)×108[6] years
TW Piscis Austrini
Mass
0.725 ± 0.036[4] M☉
Radius
0.629 ± 0.051[4] R☉
Luminosity
0.19[6] L☉
Temperature
4,711 ± 134[4] K
Rotational velocity (v sin i)
2.93[4] km/s
Age
4.4 × 108[6] years
Other designations
Fomalhaut: α Piscis Austrini, α PsA, Alpha PsA, 24 Piscis Austrini, CPD −30° 6685, FK5 867, Gl 881, HD 216956, HIP 113368, HR 8728, SAO 191524
TW Piscis Austrini: Fomalhaut B, TW PsA, Gl 879, HR 8721, CD -32°17321, HD 216803, LTT 9283, GCTP 5562.00, SAO 214197, CP(D)-32 6550, HIP 113283
LP 876-10: Fomalhaut C, 2MASS J22480446-2422075, NLTT 54872, GSC 06964-01226
Database references
Fomalhaut
SIMBAD
data
Exoplanet Archive
data
ARICNS
data
Extrasolar Planets
Encyclopaedia
data
TW Piscis Austrini
SIMBAD
data
ARICNS
data
Fomalhaut (Alpha Piscis Austrini, Alpha PsA, α Piscis Austrini, α PsA) is the brightest star in the constellation Piscis Austrinus and one of the brightest stars in the sky. It is a class A star on the main sequence approximately 25 light-years (7.7 pc) from Earth as measured by the Hipparcos astrometry satellite.[10] Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.[11] It is classified as a Vega-like star that emits excess infrared radiation, indicating it is surrounded by a circumstellar disk.[12] Fomalhaut, K-type star TW Piscis Austrini and M-type star LP 876-10 constitute a trinary system.[13]
Fomalhaut holds a special significance in extrasolar planet research, as it is the center of the first stellar system with an extrasolar planet candidate (Fomalhaut b) imaged at visible wavelengths. The image was published in Science in November 2008.[14] Fomalhaut is the third brightest star known to have a planetary system, after Pollux and the Sun.
Contents
[hide]
Fomalhaut A[edit]
Dust ring around Fomalhaut from the Atacama Large Millimeter/submillimeter Array (ALMA)[15]
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. 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. From England the star never appears much brighter than magnitude 2.2 due to it being so close to the horizon, and from southern Alaska or Scandinavia it never rises above the horizon at all.[16] Fomalhaut can be located in these northern latitudes by the fact that the western (right-hand) side of the Square of Pegasus points to it. Continue the line from Beta to Alpha Pegasi towards the southern horizon: Fomalhaut is about 45˚ south of Alpha Pegasi, with no bright stars in between.[17]
Properties[edit]
The debris disk around the star
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.[18][19] A 2012 study gave a slightly higher age of 440±40 million years.[6] 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.[6]
Fomalhaut is slightly metal-deficient as compared to the Sun, which means it is composed of a smaller percentage of elements other than hydrogen and helium.[7] 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.[8][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.[6][20] In 2004, a stellar evolutionary model of Fomalhaut yielded a metallicity of 79%.[7] Finally, in 2008, a spectroscopic measurement gave a significantly lower value of 46%.[9]
Fomalhaut has been claimed to be one of approximately 16 stars belonging to the Castor Moving Group. This is an association of stars that 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 200±100 million years and originated from the same location.[18] Unfortunately more recent work that 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.[13] Hence, “membership” to this dynamical group has no bearing on the age of the Fomalhaut system.[13]
