Fomalhaut
Fomalhaut (UK: /ˈfɒməloʊt/, US: /ˈfoʊməlhɔːt/) 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 25 light-years (7.7 pc) from the Sun as measured by the Hipparcos astrometry satellite. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.
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/, /foʊməlˈhɔːt/ |
| Fomalhaut | |
| Right ascension | 22h 57m 39.0465s |
| Declination | −29° 37′ 20.050″ |
| Apparent magnitude (V) | 1.16 |
| TW Piscis Austrini | |
| Right ascension | 22h 56m 24.05256s |
| Declination | −31° 33′ 56.0306″ |
| Apparent magnitude (V) | 6.48 |
| LP 876-10 | |
| Right ascension | 22h 48m 04.47s |
| Declination | −24° 22′ 07.5″ |
| Apparent magnitude (V) | 12.618 |
| Characteristics | |
| Spectral type | A3 V / K5Vp / M4V |
| U−B color index | 0.08 / 1.02 / ? |
| B−V color index | 0.09 / 1.10 / 1.683 |
| Variable type | None / BY Draconis / ? |
| Astrometry | |
| Fomalhaut | |
| Radial velocity (Rv) | +6.5 km/s |
| Proper motion (μ) | RA: +328.95 mas/yr Dec.: −164.67 mas/yr |
| Parallax (π) | 129.81 ± 0.47 mas |
| Distance | 25.13 ± 0.09 ly (7.70 ± 0.03 pc) |
| Absolute magnitude (MV) | 1.72 |
| TW Piscis Austrini | |
| Radial velocity (Rv) | +6.79 km/s |
| Proper motion (μ) | RA: +330.203 mas/yr Dec.: −158.98 mas/yr |
| Parallax (π) | 131.5525 ± 0.0275 mas |
| Distance | 24.793 ± 0.005 ly (7.602 ± 0.002 pc) |
| Absolute magnitude (MV) | 7.08 |
| Details | |
| Fomalhaut | |
| Mass | 1.92±0.02 M☉ |
| Radius | 1.842±0.019 R☉ |
| Luminosity | 16.63±0.48 L☉ |
| Surface gravity (log g) | 4.21 cgs |
| Temperature | 8,590 K |
| Metallicity [Fe/H] | −0.03 to −0.34 dex |
| Rotational velocity (v sin i) | 93 km/s |
| Age | (4.4±0.4)×108 years |
| TW Piscis Austrini | |
| Mass | 0.725 M☉ |
| Radius | 0.75 R☉ |
| Luminosity | 0.19 L☉ |
| Surface gravity (log g) | 4.24 cgs |
| Temperature | 4,575 K |
| Metallicity [Fe/H] | −0.09 dex |
| Rotation | 10.3 days |
| Rotational velocity (v sin i) | 2.71 km/s |
| Age | 4.4 × 108 years |
| Other designations | |
| Fomalhaut: α Piscis Austrini, α PsA, Alpha PsA, 24 Piscis Austrini, CPD−30°685, FK5 867, GJ 881, HD 216956, HIP 113368, HR 8728, SAO 191524 | |
| TW Piscis Austrini: Fomalhaut B, TW PsA, CD−32°17321, CPD−32°6550, GJ 879, HD 216803, HIP 113283, HR 8721, SAO 214197, LTT 9283 | |
| LP 876-10: Fomalhaut C, NLTT 54872, GSC 06964-01226, 2MASS J22480446-2422075 | |
| Database references | |
| SIMBAD | AC |
| AB | |
| A (Fomalhaut) | |
| B (TW PsA) | |
| C (LP 876-10) | |
| planet b | |
| Exoplanet Archive | data |
| ARICNS | A (Fomalhaut) |
| B (TW PsA) | |
A B C Location of Fomalhaut A, B, C | |
It is classified as a Vega-like star that emits excess infrared radiation, indicating it is surrounded by a circumstellar disk. 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.
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.