TW Piscis Austrini (also Fomalhaut B) is a

dwarf star A dwarf star is a star of relatively small size and low luminosity. Most main sequence stars are dwarf stars. The meaning of the word "dwarf" was later extended to some star-sized objects that are not stars, and compact stellar remnants which are ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Piscis Austrinus Piscis Austrinus is a constellation in the southern celestial hemisphere. The name is Latin for "the southern fish", in contrast with the larger constellation Pisces, which represents a pair of fish. Before the 20th century, it was also known as ...

. It lies relatively close to the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

, at an estimated distance of 24.8

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s. To an observer on Earth the star is visually separated from its larger companion Fomalhaut A by 2 degrees—the width of four

full moon The full moon is the lunar phase when the Moon appears fully illuminated from Earth's perspective. This occurs when Earth is located between the Sun and the Moon (when the ecliptic coordinate system, ecliptic longitudes of the Sun and Moon opp ...

The TW in the name is a

variable star designation In astronomy, a variable star designation is a unique identifier given to variable stars. It uses a variation on the Bayer designation format, with an identifying label (as described below) preceding the Latin genitive of the name of the constell ...

. This is a

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as ...

of the type known as a

BY Draconis variable BY Draconis variables are variable stars of late spectral types, usually K or M, and typically belong to the main sequence. The name comes from the archetype for this category of variable star system, BY Draconis. They exhibit variations in the ...

, with surface brightness variations causing the changes as the star rotates. It varies slightly in

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

, ranging from 6.44 to 6.51 over a 10.3-day period. TW Piscis Austrini lies within a light-year of Fomalhaut A. Due to sharing the same

proper motion Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...

, and the same estimated age of approximately 440 ± 40 million years, astronomers now consider them to be elements of a multiple

star system A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a '' star cluster'' or '' galaxy'', although, broadly speak ...

. A third star, dimmer and more widely separated,

Fomalhaut C Fomalhaut C, originally designated LP 876-10, is the distant third star of the Fomalhaut system. It is about five degrees from Fomalhaut, roughly halfway between it and the Helix Nebula. It is currently from Fomalhaut A, and 3.2 light- ...

, gives the system the widest visual separation, to observers from Earth, at approximately 6 degrees. In 2019, an

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

candidate around Fomalhaut B was detected by

astrometry Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, the Milky Way. His ...

References

External links

TW Piscis Austrini
at SolStation. {{DEFAULTSORT:TW Piscis Austrini Piscis Austrinus K-type main-sequence stars BY Draconis variables Piscis Austrini, TW 216803 113283 8721 0879 Durchmusterung objects