TW Piscis Austrini
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Piscis Austrinus |
| Right ascension | 22h 56m 24.05256s |
| Declination | −31° 33′ 56.0306″ |
| Apparent magnitude (V) | 5.44–6.51 |
| Characteristics | |
| Spectral type | K5Vp |
| U−B color index | 1.02 |
| B−V color index | 1.10 |
| Variable type | BY Draconis |
| Astrometry | |
| Radial velocity (Rv) | +6.79±0.12 km/s |
| Proper motion (μ) | RA: 330.203 mas/yr Dec.: −158.602 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 | |
| Mass | 0.73+0.02 −0.01 M☉ |
| Radius | 0.688±0.034 R☉ |
| Luminosity | 0.189±0.013 L☉ |
| Temperature | 4,594±80 K |
| Metallicity [Fe/H] | −0.07±0.03 dex |
| Rotation | 10.3 days |
| Rotational velocity (v sin i) | 2.93 km/s |
| Age | 440±40 Myr |
| Other designations | |
| Fomalhaut B, TW PsA, CD−32°17321, CPD−32°6550, GJ 879, HD 216803, HIP 113283, HR 8721, SAO 214197, LTT 9283, PLX 5562.00 | |
| Database references | |
| SIMBAD | data |
| ARICNS | data |
TW Piscis Austrini (also known as Fomalhaut B) is a main sequence star in the constellation Piscis Austrinus. It lies relatively close to the Sun, at an estimated distance of 24.8 light-years (7.6 parsecs). To an observer on Earth the star is visually separated from its larger companion Fomalhaut (A) by 2 degrees—the width of four full moons.
The name TW Piscis Austrini is a variable star designation. This is a variable star of the type known as a BY Draconis variable, with surface brightness variations causing the changes as the star rotates. It varies slightly in apparent magnitude, ranging from 6.44 to 6.51 over a 10.3-day period.
TW Piscis Austrini lies within a light-year of Fomalhaut. Due to sharing the same proper motion, and the same estimated age of approximately 440 ± 40 million years, astronomers now consider them to be elements of a multiple star system. A third star, dimmer and more widely separated, Fomalhaut C, gives the system the widest visual separation, to observers from Earth, at approximately 6 degrees.