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.

FU Tauri
Observation data
Epoch       Equinox
Constellation Taurus
A
Right ascension  04h 23m 35.3912s[1]
Declination +25° 03′ 02.74″[1]
Apparent magnitude (V)
B
Right ascension  04h 23m 35.3912s[2]
Declination +25° 03′ 02.74″[2]
Apparent magnitude (V)
Characteristics
Spectral type M7.25 + M9.25[3]
Apparent magnitude (G) 15.2[1] + 20.5[2]
Variable type T Tau[4]
Astrometry
A
Proper motion (μ) RA: 6.895[1] mas/yr
Dec.: −21.026[1] mas/yr
Parallax (π)7.5981 ± 0.1497[1] mas
Distance429 ± 8 ly
(132 ± 3 pc)
B
Proper motion (μ) RA: 12.450[2] mas/yr
Dec.: −21.761[2] mas/yr
Parallax (π)7.4909 ± 1.2887[2] mas
Distanceapprox. 440 ly
(approx. 130 pc)
Details
A
Mass0.05[5] M☉
Radius1.8[5] R☉
Luminosity0.2[3] L☉
Temperature2,838[3] K
Age≤1[5] Myr
B
Mass0.015[5] M☉
Luminosity0.0039[3] L☉
Temperature2,375[3] K
Age1[5] Myr
Other designations
2MASS J04233539+2503026
Database references
SIMBADA
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.[6] 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.[7]

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.[5] 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☉.[5]

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]

gollark: How?
gollark: Why is everyone g?
gollark: I would download more RAM, but I ran out of internet and I can't download more internet.
gollark: This *is* a lot slower, I think, so try and avoid it in general.
gollark: Oh right, you probably could pick out classes that way.

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  3. Luhman, K. L.; Mamajek, E. E.; Allen, P. R.; Muench, A. A.; Finkbeiner, D. P. (2009). "Discovery of a Wide Binary Brown Dwarf Born in Isolation". The Astrophysical Journal. 691 (2): 1265. arXiv:0902.0425. Bibcode:2009ApJ...691.1265L. doi:10.1088/0004-637X/691/2/1265.
  4. Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1: B/gcvs. Bibcode:2009yCat....102025S.
  5. Stelzer, B.; Scholz, A.; Argiroffi, C.; Micela, G. (2010). "The enigmatic young brown dwarf binary FU Tau: Accretion and activity". Monthly Notices of the Royal Astronomical Society. 408 (2): 1095–1102. arXiv:1006.2717. Bibcode:2010MNRAS.408.1095S. doi:10.1111/j.1365-2966.2010.17182.x.
  6. Monin, J.-L.; Whelan, E. T.; Lefloch, B.; Dougados, C.; Alves De Oliveira, C. (2013). "A molecular outflow driven by the brown dwarf binary FU Tauri". Astronomy & Astrophysics. 551: L1. arXiv:1301.4387. Bibcode:2013A&A...551L...1M. doi:10.1051/0004-6361/201220973.
  7. "FU Tauri". Open Exoplanet Catalogue. Retrieved 2020-04-06.
  8. Romano, G. (1975). "Observations of T Tau stars and related objects in Taurus dark cloud". Memorie della Societa Astronomica Italiana. 46: 81. Bibcode:1975MmSAI..46...81R.
  9. Gotz, W. (1961). "Photographische Untersuchungen an RW Aurigae-Sternen in den Dunkelgebieten von Taurus und Orion". Veroeffentlichungen der Sternwarte Sonneberg. 5: 87. Bibcode:1961VeSon...5...87G.
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