Epoch J2000 Equinox J2000
|Declination||-31° 33′ 56.0351″|
|U-B color index||1.02|
|B-V color index||1.10|
|Variable type||BY Draconis|
|Radial velocity (Rv)||+6 km/s|
|Proper motion (?)|| RA: -331.11 mas/yr |
Dec.: -158.98 mas/yr
|Parallax (?)||131.42 ± 0.62 mas|
|Distance||24.8 ± 0.1 ly |
(7.61 ± 0.04 pc)
|Absolute magnitude (MV)||7.08|
|Rotational velocity (v sin i)||2.93 km/s|
|Age||4.4 × 108 years|
TW Piscis Austrini (also Fomalhaut B) is a dwarf star in the constellation Piscis Austrinus. It lies relatively close to the Sun, at an estimated distance of 24.9 light years. 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 TW in the name is astronomical nomenclature for a variable star. This 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.
TW Piscis Austrini lies within a light year of Fomalhaut A. 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.
Though it may appear isolated in the barren October sky, Fomalhaut has company. It feels the gravitational tug of the magnitude +6.5 star TW Piscis Austrini, 2° to the south. Both are 25 light-years distant and move in tandem across space, partaking of the same proper motion. They form a true double star with an actual separation of 5.5 trillion miles, or 0.91 light-years.
Believe it or not, an extrasolar planet might also be circling TW Piscis Austrini. NASA's Transiting Exoplanet Survey Satellite (TESS), a space telescope that's searching for planets around the brightest stars in Earth's night sky, recently found a possible candidate circling this star. It's almost the same size as our Earth, and orbits the star about every 10 days at a distance of 7.5 million miles from it.