XO-2 is a

binary star A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...

system about away in the constellation

Lynx A lynx ( ; : lynx or lynxes) is any of the four wikt:extant, extant species (the Canada lynx, Iberian lynx, Eurasian lynx and the bobcat) within the medium-sized wild Felidae, cat genus ''Lynx''. The name originated in Middle Engl ...

. It consists of two components, XO-2N and XO-2S, both of which host

planetary system A planetary system is a set of gravity, gravitationally bound non-stellar Astronomical object, bodies in or out of orbit around a star or star system. Generally speaking, systems with one or more planets constitute a planetary system, although ...

Star system

This system is unusual in that the stars are not typically referred to as components A & B, but are designated based on their positions in the sky: XO-2N is the northern star and XO-2S is the southern star. Both of the stars are slightly cooler than the Sun and are nearly identical to each other. The system has a

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

of 11 and cannot be seen with the naked eye but is visible through a small

telescope A telescope is a device used to observe distant objects by their emission, Absorption (electromagnetic radiation), absorption, or Reflection (physics), reflection of electromagnetic radiation. Originally, it was an optical instrument using len ...

. These stars are also notable for their large

proper motion Proper motion is the astrometric measure of changes in the apparent places of stars or other celestial objects as they move relative to the center of mass of the Solar System. It is measured relative to the distant stars or a stable referenc ...

s. XO-2N and XO-2S have a separation of approximately AU.

Planetary systems

There is one confirmed

exoplanet 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 det ...

orbiting XO-2N. XO-2Nb, which is classified as a

hot Jupiter Hot Jupiters (sometimes called hot Saturns) are a class of gas giant exoplanets that are inferred to be physically similar to Jupiter (i.e. Jupiter analogue, Jupiter analogues) but that have very short orbital periods (). The close proximity to t ...

, was discovered by the

XO Telescope The XO Project is an international team of amateur and professional astronomers tasked with identifying extrasolar planets. They are led by Peter R. McCullough of the Space Telescope Science Institute. It is primarily funded by NASA's Origins Pro ...

using the

transit method Methods of detecting exoplanets usually rely on indirect strategies – that is, they do not directly image the planet but deduce its existence from another signal. Any planet is an extremely faint light source compared to its parent star. For e ...

around XO-2N in 2007. It was initially the only known planet in the system and was referred to as XO-2b. A long-period variation in the

radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity ...

of XO-2N was detected in 2015, which could be explained by either a second planet or a stellar activity cycle. The stellar activity explanation is considered more likely, and is further supported by a 2024 study. Two planets were reported to orbit around XO-2S in 2014 using the

radial velocity method Doppler spectroscopy (also known as the radial-velocity method, or colloquially, the wobble method) is an indirect method for finding extrasolar planets and brown dwarfs from radial-velocity measurements via observation of Doppler shifts in th ...

. One of them is Jupiter-mass and another has a mass comparable to Saturn. A 2024 study found evidence for a third,

super-Jupiter A super-Jupiter is a gas giant exoplanet that is more massive than the planet Jupiter. For example, substellar companion, companions at the planet–brown dwarf borderline have been called super-Jupiters, such as around the star Kappa Andromedae. ...

mass planet around XO-2S.

Notes

References

External links

* NASA PlanetQuest
Planet race heats up: 1 month, 32 discoveries
* {{DEFAULTSORT:XO-2 (star) K-type main-sequence stars Lynx (constellation) Planetary transit variables Planetary systems with four confirmed planets 2 Binary stars BD+50 1471

1720 Events January–March * January 21 – Sweden and Prussia sign the Treaty of Stockholm (Great Northern War). * February 10 – Edmond Halley is appointed as Astronomer Royal for England. * February 17 – The Treaty o ...

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Star system

Planetary systems

See also

Notes

References

Further reading

External links