Kappa Crucis (κ Cru, HD 111973) is a spectroscopic binary

star A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth make ...

in the

open cluster An open cluster is a type of star cluster made of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...

NGC 4755, which is also known as the Kappa Crucis Cluster or Jewel Box Cluster.

Location

A Snapshot of the Jewel Box cluster with the ESO VLT

κ Crucis is one of the brightest members of the open cluster that bears its name, better known as the Jewel Box Cluster. It forms one leg, at bottom right or south, of the prominent letter "A" asterism at the centre of the cluster. The cluster is part of the larger Centaurus OB1 association and lies about 8,500

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 101 ...

s away. The cluster, and κ Cru itself, is just to the south-east of

β Crucis Mimosa is the second-brightest object in the southern constellation of Crux (after Acrux), and the 20th-brightest star in the night sky. It has the Bayer designation β Crucis, which is Latinised to Beta Crucis and abbreviated Beta Cru ...

, the lefthand star of the famous

Southern Cross 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 ...

Properties

κ Crucis is a B3 bright supergiant (luminosity class Ia).

Radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the rate of change of the distance or range between the two points. It is equivalent to the vector projection ...

variations in the

spectral line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...

s indicate that it has an unresolved companion star. It is over 100,000 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 nomin ...

, partly due to its higher temperature over , and partly to its larger size. The κ Crucis cluster has a calculated age of 11.2 million years.

References

External links

* {{DEFAULTSORT:Kappa Crucis (star) Crux (constellation) Crucis, Kappa 111973 B-type supergiants 062931 4890 Durchmusterung objects J12534890-6022344 Spectroscopic binaries