Kappa Crucis (star)

Kappa Crucis (κ Cru, HD 111973) is a spectroscopic binary star in the open cluster NGC 4755, which is also known as the Kappa Crucis Cluster or Jewel Box Cluster.

κ Crucis

The centre of NGC 4755, with κ Cru on the left Credit: NASA/ESA and Jesús Maíz Apellániz (Instituto de Astrofísica de Andalucía, Spain)
Observation data Epoch J2000      Equinox J2000
Constellation	Crux
Right ascension	12h 53m 48.91920s[1]
Declination	−60° 22′ 34.4808″[1]
Apparent magnitude (V)	5.98[2]
Characteristics
Spectral type	B3Ia[3]
U−B color index	−0.58[2]
B−V color index	+0.22[2]
Astrometry
Radial velocity (Rv)	-3.5[4] km/s
Proper motion (μ)	RA: −5.046[5] mas/yr Dec.: −1.093[5] mas/yr
Parallax (π)	0.4334±0.0481 mas[5]
Distance	approx. 7,500 ly (approx. 2,300 pc)
Absolute magnitude (MV)	−7.1[6]
Details[7]
Mass	23.0 M☉
Luminosity	151,000 L☉
Surface gravity (log g)	2.25 cgs
Temperature	16,300 K
Rotational velocity (v sin i)	70 km/s
Other designations
κ Cru, CD−59°4460, HD 111973, HIP 62931, HR 4890, SAO 252077, 2MASS J12534890-6022344
Database references
SIMBAD	data

Location

A snapshot of the Jewel Box Cluster (Credit: 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.^[8] 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-years away.

The cluster, and κ Cru itself, is just to the south-east of β Crucis, the lefthand star of the famous Southern Cross.

Properties

κ Crucis is a B3 bright supergiant (luminosity class Ia). Radial velocity variations in the spectral lines indicate that it has an unresolved companion star.^[9] It is over 100,000 times the luminosity of the Sun, partly due to its higher temperature over 16,300 K, and partly to its larger size. The κ Crucis cluster has a calculated age of 11.2 million years.^[10]