UScoCTIO 108 is a

binary system A binary system is a system of two astronomical bodies of the same kind that are comparable in size. Definitions vary, but typically require the center of mass to be located outside of either object. (See animated examples.) The most common ki ...

, approximately 470

light-years A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astro ...

away in the Upper Scorpius (USco) OB association. The primary, UScoCTIO 108A, with mass around 0.06

solar masses The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies ...

, is a

brown dwarf Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main sequence, main-sequence stars. Their mass is approximately 13 to 80 Jupiter mass, times that of Jupiter ()not big en ...

or low-mass

red dwarf A red dwarf is the smallest kind of star on the main sequence. Red dwarfs are by far the most common type of fusing star in the Milky Way, at least in the neighborhood of the Sun. However, due to their low luminosity, individual red dwarfs are ...

. The secondary, UScoCTIO 108B, with a mass around the deuterium burning limit of 13

Jupiter masses The Jupiter mass, also called Jovian mass, is the unit of mass equal to the total mass of the planet Jupiter. This value may refer to the mass of the planet alone, or the mass of the entire Jovian system to include the moons of Jupiter. Jupiter i ...

, would be classified as either a

or an

extrasolar planet An exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first detect ...

. 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 The Cerro Tololo Inter-American Observatory (CTIO) is an Astronomy, astronomical observatory located on the summit of Mt. Cerro Tololo in the Coquimbo Region of northern Chile, with additional facilities located on Mt. Cerro Pachón about to th ...

(CTIO), where it received the designation ''UScoCTIO 108''. 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 The Jupiter mass, also called Jovian mass, is the units of mass, unit of mass equal to the total mass of the planet Jupiter. This value may refer to the mass of the planet alone, or the mass of the entire Jovian system to include the moons of Jup ...

(''M''_J), an

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of 2,800 K and a

spectral type In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

of M7. The low mass indicates that the object is not able to sustain

hydrogen fusion In astrophysics, stellar nucleosynthesis is the creation of chemical elements by nuclear fusion reactions within stars. Stellar nucleosynthesis has occurred since the original creation of hydrogen, helium and lithium during the Big Bang. As a ...

, making it a brown dwarf. The secondary member of the system was found in 2008 as an object located at a separation of 4.6

arcsecond A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of a degree. Since one degree is of a turn, or complete rotation, one arcminute is of a tu ...

s, which corresponds to a physical separation of more than 670 AU, and is also a confirmed member of the Upper Scorpius association. Its spectrum shows it is also a cold

substellar object A substellar object, sometimes called a substar, is an astronomical object, the mass of which is smaller than the smallest mass at which hydrogen fusion can be sustained (approximately 0.08 solar masses). This definition includes brown dwarfs and f ...

, with an effective temperature of 2,300 K and a spectral type of M9.5. Its mass was originally estimated at 14 ''M''_J, very close to the nominal boundary between

planet A planet is a large, Hydrostatic equilibrium, rounded Astronomical object, astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets b ...

s 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. The physical association between the two brown dwarfs has not been confirmed by observation of

common proper motion This glossary of astronomy is a list of definitions of terms and concepts relevant to astronomy and cosmology, their sub-disciplines, and related fields. Astronomy is concerned with the study of astronomical object, celestial objects and phenomena ...

, but is considered very likely given the proximity between them. 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 In celestial mechanics, escape velocity or escape speed is the minimum speed needed for an object to escape from contact with or orbit of a primary body, assuming: * Ballistic trajectory – no other forces are acting on the object, such as ...

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

perturbation Perturbation or perturb may refer to: * Perturbation theory, mathematical methods that give approximate solutions to problems that cannot be solved exactly * Perturbation (geology), changes in the nature of alluvial deposits over time * Perturbati ...

s by passing stars will cause the rupture of the system in a few million years. Observations by the

infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...

telescope WISE revealed excess emission at 12 and 22

μm The micrometre (Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a unit of length in the International System ...

, indicating the presence of a

debris disk A debris disk (American English), or debris disc ( Commonwealth English), is a circumstellar disk of dust and debris in orbit around a star. Sometimes these disks contain prominent rings, as seen in the image of Fomalhaut on the right. Debris ...

around the brown dwarf.

References

External links

Star: UScoCTIO 108
''Extrasolar Planets Encyclopaedia''. Accessed on line June 17, 2008. {{Stars of Scorpius Brown dwarfs M-type main-sequence stars Scorpius Upper Scorpius

See also

References

External links