UScoCTIO 108

UScoCTIO 108 is a binary system, approximately 470 light-years away in the Upper Scorpius (USco) OB association. The primary, UScoCTIO 108A, with mass around 0.06 solar masses, is a brown dwarf or low-mass red dwarf. The secondary, UScoCTIO 108B, with a mass around the deuterium burning limit of 13 Jupiter masses, would be classified as either a brown dwarf or an extrasolar planet.[2]

UScoCTIO 108A
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Scorpius
Right ascension  16h 05m 53.94s[1]
Declination −18° 18′ 42.7″[1]
Characteristics
Spectral type M7[2]
Astrometry
Proper motion (μ) RA: -7.4 ± 4.6[3] mas/yr
Dec.: -20.4 ± 4.6[3] mas/yr
Distance473 ± 6 ly
(145 ± 2[2] pc)
Details
Mass0.057 ± 0.019[2][2] M☉
Luminosity0.011+0.06
−0.03[2] L☉
Temperature2700 ± 100[2] K
Radius0.46 R☉
Database references
SIMBADdata
UScoCTIO 108B
Position (relative to A)
Epoch of observationJ2007.5
Angular distance4.6 ± 0.1″ [2]
Position angle177 ± 1° [2]
Observed separation
(projected)		~670 AU [2]
Characteristics
Spectral type M9.5 ± 0.5[4]
Details
Mass0.015+0.009
−0.004[4] M☉
Radius0.16 ± 0.01[4] R☉
Luminosity0.00065 ± 0.00007[4] L☉
Surface gravity (log g)4.0 ± 0.5[4] cgs
Temperature2300 ± 100[4] K
Other designations
UscoCTIO 108b[5]
Database references
SIMBADdata

The primary component of the system was discovered in 2000 as a possible member of the Upper Scorpius association, based on its position in a HR diagram, in a search for new member of the association by the Cerro Tololo Inter-American Observatory (CTIO), where it received the designation UScoCTIO 108.[6] Later, spectroscopic and photometric observations confirmed that the object is a real member of the association, showing signs of low gravity and youth, and estimated a mass of 60 times the mass of Jupiter (MJ), an effective temperature of 2,800 K and a spectral type of M7. The low mass indicates that the object is not able to sustain hydrogen fusion, making it a brown dwarf.[2]

The secondary member of the system was found in 2008 as an object located at a separation of 4.6 arcseconds, which corresponds to a physical separation of more than 670 AU, and is also a confirmed member of the Upper Scorpius association.[2] Its spectrum shows it is also a cold substellar object, with an effective temperature of 2,300 K and a spectral type of M9.5.[4] Its mass was originally estimated at 14 MJ,[2] very close to the nominal boundary between planets and brown dwarf, but a recent revision of the age of the Upper Scorpius association to 11 million years increased this value to 16 MJ, indicating that the object is likely a low mass brown dwarf.[7] The physical association between the two brown dwarfs has not been confirmed by observation of common proper motion, but is considered very likely given the proximity between them.[2][3]

The minimum separation between the two brown dwarfs, 670 AU, is much larger than the mean of other similar mass systems, and indicates that the pair (if they really form a binary system) is very weakly bound, with an escape velocity for the secondary component of only 0.4 km/s. Considering the average stellar density in an association like Upper Scorpius, it is estimated that perturbations by passing stars will cause the rupture of the system in a few million years.[2]

Observations by the infrared telescope WISE revealed excess emission at 12 and 22 μm, indicating the presence of a debris disk around the brown dwarf.[8]

See also

References
  1. UScoCTIO 108, entry, SIMBAD. Accessed on line June 17, 2008.
  2. V. J. S. Bejar; M. R. Zapatero Osorio; A. Perez-Garrido; C. Álvarez; et al. (February 2008). "Discovery of a Wide Companion near the Deuterium-burning Mass Limit in the Upper Scorpius Association". Astrophysical Journal. 673 (2): L185–L189. arXiv:0712.3482. Bibcode:2008ApJ...673L.185B. doi:10.1086/527557.
  3. Ginski, C.; et al. (November 2014). "Astrometric follow-up observations of directly imaged sub-stellar companions to young stars and brown dwarfs". Monthly Notices of the Royal Astronomical Society. 444 (3): 2280–2302. arXiv:1409.1850. Bibcode:2014MNRAS.444.2280G. doi:10.1093/mnras/stu1586.
  4. Bonnefoy, M.; et al. (February 2014). "A library of near-infrared integral field spectra of young M-L dwarfs". Astronomy & Astrophysics. 562: A127, 26 pp. arXiv:1306.3709. Bibcode:2014A&A...562A.127B. doi:10.1051/0004-6361/201118270.
  5. NAME UScoCTIO 108b, entry, SIMBAD. Accessed on line June 17, 2008.
  6. Ardila, David; Martín, Eduardo; Basri, Gibor (July 2000). "A Survey for Low-Mass Stars and Brown Dwarfs in the Upper Scorpius OB Association". The Astronomical Journal. 120 (1): 479–487. arXiv:astro-ph/0003316. Bibcode:2000AJ....120..479A. doi:10.1086/301443.CS1 maint: multiple names: authors list (link)
  7. Pecaut, Mark J.; Mamajek, Eric E.; Bubar, Eric J. (February 2012). "A Revised Age for Upper Scorpius and the Star Formation History among the F-type Members of the Scorpius-Centaurus OB Association". The Astrophysical Journal. 746 (2): article 154, 22 pp. arXiv:1112.1695. Bibcode:2012ApJ...746..154P. doi:10.1088/0004-637X/746/2/154.
  8. Morales, Farisa Y.; Padgett, D. L.; Bryden, G.; Werner, M. W.; Furlan, E. (September 2012). "WISE Detections of Dust in the Habitable Zones of Planet-bearing Stars". The Astrophysical Journal. 757 (1): artigo 7, 6 pp. Bibcode:2012ApJ...757....7M. doi:10.1088/0004-637X/757/1/7.
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