Eta Crucis (η Crucis) is a solitary star in the southern constellation of

Crux Crux () is a constellation of the southern sky that is centred on four bright stars in a cross-shaped asterism commonly known as the Southern Cross. It lies on the southern end of the Milky Way's visible band. The name ''Crux'' is Latin for ...

. It can be seen with the naked eye, having an

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's lig ...

of 4.14^m. Based upon parallax measurements, η Crucis is located 64 light-years from the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

. The system made its closest approach about 1.6 million years ago when it achieved

perihelion An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any elli ...

at a distance of roughly 26 light years. This is an

F-type main sequence star An F-type main-sequence star (F V) is a main-sequence, hydrogen-fusing star of spectral type F and luminosity class V. These stars have from 1.0 to 1.4 times the mass of the Sun and surface temperatures between 6,000 and 7,600 K.Tables VI ...

with a stellar classification of F2 V. It has 130% of the Sun's radius and shines with 7 times the

luminosity of the Sun 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 ...

from an outer atmosphere with an effective temperature of 6,964 K. Observations of the system using the Spitzer Space Telescope show a statistically significant

infrared excess An infrared excess is a measurement of an astronomical source, typically a star, that in their spectral energy distribution has a greater measured infrared flux than expected by assuming the star is a blackbody radiator. Infrared excesses are oft ...

of emission at a wavelength of 70 μm. This suggests the presence of a

circumstellar disk A circumstellar disc (or circumstellar disk) is a torus, pancake or ring-shaped accretion disk of matter composed of gas, dust, planetesimals, asteroids, or collision fragments in orbit around a star. Around the youngest stars, they are the ...

. The temperature of this material is below 70 K. Eta Crucis has a pair of visual companions. Component B is a magnitude 11.80 star located at an angular separation of 48.30 ″ along a

position angle In astronomy, position angle (usually abbreviated PA) is the convention for measuring angles on the sky. The International Astronomical Union defines it as the angle measured relative to the north celestial pole (NCP), turning positive into the ...

of 300°, as of 2010. Component C has a magnitude of 12.16 and lies at an angular separation of 35.50″ along a position angle of 194°, as of 2000.

References

External links

* {{DEFAULTSORT:Eta Crucis Crucis, Eta Crux (constellation) F-type main-sequence stars 105211 059072 4616 Durchmusterung objects Gliese and GJ objects