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 108

UScoCTIO 108A is the yellow object in the middle and the B component is the orange object below Credit: legacy surveys
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]+M9.5
Astrometry
Proper motion (μ)	RA: -7.4 ± 4.6[3] mas/yr Dec.: -20.4 ± 4.6[3] mas/yr
Distance	473 ± 6 ly (145 ± 2[2] pc)
Details
A
Mass	0.057 ± 0.019[2] M☉
Radius	0.46 R☉
Luminosity	0.011+0.06 −0.03[2] L☉
Temperature	2700 ± 100[2] K
Age	11 Myr
B
Mass	14 MJup
Temperature	2300 K
Database references
SIMBAD	data

UScoCTIO 108B

UScoCTIO 108 B's orbit
Position (relative to A)
Epoch of observation	J2007.5
Angular distance	4.6 ± 0.1″ [2]
Position angle	177 ± 1° [2]
Projected separation	~670 AU [2]
Characteristics
Spectral type	M9.5 ± 0.5[4]
Details
Mass	0.015+0.009 −0.004[4] M☉
Mass	15.79 MJup
Radius	0.16 ± 0.01[4] R☉
Radius	1.557 RJup
Luminosity	0.00065 ± 0.00007[4] L☉
Surface gravity (log g)	4.0 ± 0.5[4] cgs
Temperature	2300 ± 100[4] K
Orbit
Primary	UScoCTIO 108 A
Semi-major axis (a)	670 AU
Other designations
UscoCTIO 108b[5]
Database references
SIMBAD	data

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 (M_J), 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 M_J,^[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 M_J, 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

• SDSS J1416+1348
• 2M1101AB
• Oph 162225-240515
• Binary brown dwarfs