AA Tauri is a young

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 e ...

in the equatorial

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

of Taurus, located in the Taurus-Auriga star-forming region. It is too faint to view with the naked eye, having an

apparent visual 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 lig ...

that varies from 12.2 down to 16.1. The star is located approximately 447

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 away from 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 ...

based on

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby object ...

, and is drifting further away with a

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the rate of change of the distance or range between the two points. It is equivalent to the vector projection ...

of +17 km/s. The

stellar classification In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

for this object is K7Ve, matching a

K-type main-sequence star A K-type main-sequence star, also referred to as a K-type dwarf or an orange dwarf, is a main-sequence ( hydrogen-burning) star of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence s ...

that displays emission features. It is an eruptive variable of the T Tauri type with an estimated age of 2.4 million years. The object has 76% of the

mass of the Sun The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...

, 181% of the Sun's radius, and is spinning with a

projected rotational velocity Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface. The rotation of a star produces an equatorial bulge ...

of 13 km/s. AA Tauri is radiating 80% of the

luminosity of the Sun The solar luminosity (), is a unit of radiant flux ( power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun. One nominal ...

at an

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of 4,060 K.

Variability

AA Tauri shows brightness variations of one to two magnitudes over an 8.2-day period. The brightness has been described as "roughly constant, interrupted by quasi-cyclic fading episodes". The periodic variations are ascribed to eclipses of the star by a warped dust disk around it. In 2011, AA Tauri faded by about two magnitudes and has remained at the fainter level since then. The star also became significantly more reddened. The eight-day variations continue, with a maximum brightness now around magnitude 14 and magnitude 16.5 at its faintest. It is theorised that the root cause of this dimness is a warp in the

accretion disk An accretion disk is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a massive central body. The central body is typically a star. Friction, uneven irradiance, magnetohydrodynamic effects, and other ...

, located at a distance of 7.7 AU or more from the centre, that was brought into the line of sight by its elliptical motion around the central star.

A possible planetary system

In their paper of 2003, Grinin et al. invoke the possible presence of a substellar object to explain peculiar and periodic eclipses occurring to the young star every 8.3 days. They infer a mass of 20 times that of

Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousand ...

for the perturbing object and an orbital separation of 0.08

Astronomical Unit The astronomical unit (symbol: au, or or AU) is a unit of length, roughly the distance from Earth to the Sun and approximately equal to or 8.3 light-minutes. The actual distance from Earth to the Sun varies by about 3% as Earth orbits ...

s. Later studies find no evidence for a planet, instead finding multiple rings with accretion streams between them.

References

{{DEFAULTSORT:AA Tauri K-type main-sequence stars T Tauri stars Hypothetical planetary systems Taurus (constellation) Tauri, AA J04345542+2428531 IRAS catalogue objects