HD 102365 (66 G. Centauri) 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 that is located in the northeastern part of the

Centaurus Centaurus () is a bright constellation in the southern sky. One of the 88 modern constellations by area, largest constellations, Centaurus was included among the 48 constellations listed by the 2nd-century astronomer Ptolemy, and it remains one ...

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

, at a distance of about from the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

. The larger member of the system is a G-type star that is smaller than the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

but of similar mass. It has a

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 ...

companion that was discovered by W. J. Luyten in 1960. This M-type star appears to be in a wide orbit around the primary at a current separation of about 211

astronomical unit The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its m ...

s (AU), (or 211 times the separation of the Earth from the Sun). By comparison,

Neptune Neptune is the eighth and farthest known planet from the Sun. It is the List of Solar System objects by size, fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 t ...

orbits at an average distance of 30 AU.

Description

The

stellar classification 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 gratin ...

for the primary star in this system is G2V; the same as the Sun. That of the

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 ...

companion is M4V. The primary star has an estimated 84% the

mass of the Sun 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 a ...

, 99% of the

Sun's radius Solar radius is a unit of distance used to express the size of objects in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: 1\,R_ = 6.957\ti ...

, and 86% of the

Sun's luminosity The solar luminosity () is a unit of radiant flux ( power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun. One nominal s ...

. It is a slow rotator, with a

projected rotational velocity Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface. The rotation of a star produces an equatorial bu ...

of 0.5 km/s. Age estimates range from 4.5 to 5.7 billion years (Gyr) up to 7.1 Gyr or 9.48 Gyr. Compared to the Sun, it only has about 52% of the abundance of elements other than hydrogen and helium; what astronomers term the

metallicity In astronomy, metallicity is the Abundance of the chemical elements, abundance of Chemical element, elements present in an object that are heavier than hydrogen and helium. Most of the normal currently detectable (i.e. non-Dark matter, dark) matt ...

of a star. This star system has a relatively large proper motion. The HR 4523 system is presently located within the Epsilon Indi Moving Group, although it gives itself away as an interloper, since the star is older and has a different composition than the group members. It has space velocity components = .

Planetary system

The primary star is believed to be orbited by a Neptune-like planet with a

minimum mass In astronomy, minimum mass is the lower-bound calculated mass of observed objects such as planets, stars, binary systems, nebulae, and black holes. Minimum mass is a widely cited statistic for extrasolar planets detected by the radial velocit ...

16 times that of the Earth. The orbital period of this planet is 122.1 days. No other planets have been discovered orbiting this star. While a 2013 study was unable to confirm this planet, it was confirmed by a 2023 study. An examination of this system in 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 ...

did not reveal an excess emission that would otherwise suggest the presence of a circumstellar

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 ...

References

External links

* {{DEFAULTSORT:HD 102365 G-type main-sequence stars HR, 4523 Planetary systems with one confirmed planet M-type main-sequence stars Binary stars Centaurus CD-39 07301 0442 Centauri, 66 102365 057433 4523