FU Tauri
Brown dwarf binary star system in the constellation Taurus
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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.
FU Tauri and its companion (lower left) Credit: Image Credit: NASA/ESA/CSA JWST; Ya-Lin Wu et al.; processing: Meli_thev | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Taurus |
| A | |
| Right ascension | 04h 23m 35.3912s[1] |
| Declination | +25° 03′ 02.74″[1] |
| B | |
| Right ascension | 04h 23m 35.3912s[1] |
| Declination | +25° 03′ 02.74″[1] |
| Characteristics | |
| Spectral type | M7.25 + M9.25[2] |
| Apparent magnitude (G) | 15.2[1] + 20.5[1] |
| Variable type | T Tau[3] |
| Astrometry | |
| A | |
| Proper motion (μ) | RA: 6.895[1] mas/yr Dec.: −21.026[1] mas/yr |
| Parallax (π) | 7.5981±0.1497 mas[1] |
| Distance | 429 ± 8 ly (132 ± 3 pc) |
| B | |
| Proper motion (μ) | RA: 12.450[1] mas/yr Dec.: −21.761[1] mas/yr |
| Parallax (π) | 7.4909±1.2887 mas[1] |
| Distance | approx. 440 ly (approx. 130 pc) |
| Details | |
| A | |
| Mass | 0.05[4] M☉ |
| Radius | 1.8[4] R☉ |
| Luminosity | 0.2[2] L☉ |
| Temperature | 2,838[2] K |
| Age | ≤1[4] Myr |
| B | |
| Mass | 0.015[4] M☉ |
| Luminosity | 0.0039[2] L☉ |
| Temperature | 2,375[2] K |
| Age | 1[4] Myr |
| Other designations | |
| WDS J04236+2503A, 2MASS J04233539+2503026, Gaia DR2 149629483705467008 | |
| Database references | |
| SIMBAD | A |
| B | |
System
The two stars of the FU Tauri system are separated by 5.7″, equivalent to 800 AU at the distance of FU Tauri.[5] The primary is a brown dwarf with a mass of 0.05 M☉, while the secondary has a mass of 0.015 M☉. The secondary mass of 15 MJ is close to the dividing line between brown dwarfs and exoplanets, and it is often treated as an exoplanet.[6]
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.[4] The primary has a temperature of 2,838 K, a radius of 1.8 R☉, and a bolometric luminosity of 0.2 L☉. The secondary has a temperature of 2,375 K and a bolometric luminosity of 0.0039 L☉.[4]
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.[8] Its photographic magnitude has been measured to vary between magnitude 15.1 and below magnitude 17.6.[9]