The TW Hydrae association is a group of very young low-mass

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

s and

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 fo ...

s located approximately 25–75

parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and ...

s (80–240

light year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s) from Earth. They share a common motion and appear to all be roughly the same age, 10±3 million years old. It is the youngest such

association Association may refer to: *Club (organization), an association of two or more people united by a common interest or goal *Trade association, an organization founded and funded by businesses that operate in a specific industry *Voluntary associatio ...

within 100 pc from Earth. As of 2017, 42 objects (in 23 systemsSingular objects are also regarded as "systems" here.) are assigned to the association confidently, and several dozens — uncertainly. Masses of its known members vary from 5

Jupiter mass 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 is b ...

es to 2

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

es, and their

spectral type In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction grati ...

s vary from A0 to L7. Some of the best studied members of this stellar association are

TW Hydrae TW Hydrae is a T Tauri star approximately 196 light-years away in the constellation of Hydra (the Sea Serpent). TW Hydrae is about 80% of the mass of the Sun, but is only about 5-10 million years old. The star appears to be accreting fr ...

(nearest known accreting

T Tauri star T Tauri stars (TTS) are a class of variable stars that are less than about ten million years old. This class is named after the prototype, T Tauri, a young star in the Taurus star-forming region. They are found near molecular clouds and iden ...

to the Earth),

HR 4796 HR 4796 is a binary star, binary star system in the southern constellation of Centaurus (constellation), Centaurus. Parallax measurements put it at a distance of from the Earth. The two components of this system have an angular separatio ...

(an A-type star with resolved dusty debris disk; the most massive known group member),

HD 98800 HD 98800, also catalogued as TV Crateris (TV Crt), is a quadruple star system in the constellation of Crater (the cup). Parallax measurements made by the Hipparcos spacecraft put it at a distance of about 150 light-years (45 pars ...

(a quadruple star system with debris disk), and

2M1207 2M1207, 2M1207A or 2MASSW J12073346–3932539 is a brown dwarf located in the constellation Centaurus; a companion object, 2M1207b, may be the first extrasolar planetary-mass companion to be directly imaged, and is the first discovered ...

(accreting brown dwarf with remarkable planetary-mass companion

2M1207b 2M1207b is a planetary-mass object orbiting the brown dwarf 2M1207, in the constellation Centaurus, approximately 170 light-years from Earth.

). Included in the association is WISEA 1147, which is a

brown dwarf Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...

References

{{reflist, refs= {{cite journal , title =BANYAN. IX. The Initial Mass Function and Planetary-mass Object Space Density of the TW HYA Association , author =Gagné, J. , author2=Faherty, J. K., author2-link=Jackie Faherty , author3=Mamajek, E. E., display-authors=etal , date =2017 , journal=The Astrophysical Journal Supplement Series , volume =228 , issue =2 , pages =1–62 (look p. 26, 35) , doi =10.3847/1538-4365/228/2/18 , bibcode=2017ApJS..228...18G , arxiv =1612.02881 Stellar associations Star-forming regions

See also

References