FU Tauri

FU Tauri is a brown dwarf binary system in the constellation of Taurus about $429 light years$ away. The secondary is very close to the lower limit for brown dwarfs and several databases list it as a distant massive exoplanet.

System
The two stars of the FU Tauri system are separated by $5.7 "$, equivalent to $800 AU$ at the distance of FU Tauri. The primary is a brown dwarf with a mass of, while the secondary has a mass of. The secondary mass of is close to the dividing line between brown dwarfs and exoplanets, and it is often treated as an exoplanet.

Properties
Both members of the binary are low-mass objects still contracting towards the main sequence. Comparison with theoretical evolutionary tracks gives them ages of one Myr or less. However, the primary is more luminous than expected even for this age and it may be younger than the secondary. The primary has a temperature of $2,838 K$, a radius of, and a bolometric luminosity of. The secondary has a temperature of $2,375 K$ and a bolometric luminosity of.

Variability
FU Tauri varies in brightness. The primary star is a T Tauri variable, a type of irregular pre-main-sequence star. Its brightness has been observed to vary from a photovisual magnitude of 16.0 to fainter than 17.0. Its photographic magnitude has been measured to vary between magnitude 15.1 and below magnitude 17.6.