DU Crucis

DU Crucis is a red supergiant and slow irregular variable star in the open cluster NGC 4755, which is also known as the Kappa (κ) Crucis Cluster or Jewel Box Cluster.

DU Crucis

The centre of NGC 4755, with DU Cru at top right 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 41.33485s[1]
Declination	−60° 20′ 57.9647″[1]
Apparent magnitude (V)	7.45[2]
Characteristics
Spectral type	M2- Iab[3]
U−B color index	+2.57[2]
B−V color index	+2.22[2]
Variable type	Lc[4]
Astrometry
Radial velocity (Rv)	−21.24[5] km/s
Proper motion (μ)	RA: −4.703[6] mas/yr Dec.: −1.162[6] mas/yr
Parallax (π)	0.5075±0.0516 mas[6]
Distance	2,600[7][8] pc
Absolute magnitude (MV)	−5.52[9]
Details[10]
Radius	664 R☉
Luminosity	69,600 L☉
Temperature	3,467[9] K
Other designations
DU Cru, CD−59°4459, HIP 62918, SAO 252073, 2MASS J12534132-6020578, IRAS 12506-6004
Database references
SIMBAD	data

Location

A Snapshot of the Jewel Box cluster (Credit: ESO VLT).

DU Crucis is one of the brighter members of the Jewel Box Cluster and the brightest red supergiant, strongly contrasting with the other bright members which are blue supergiants.^[11] It is part of the central bar of the prominent letter A-shaped 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 is just to the south-east of β Crucis, the lefthand star of the Southern Cross.

Properties

DU Crucis is an M2 intermediate luminosity supergiant (luminosity class Iab). Despite its low temperature, it is 46,600 times the luminosity of the sun, due to its very large size. The κ Crucis cluster has a calculated age of 11.2 million years.^[7]

Variability

A light curve for DU Crucis, plotted from Hipparcos data^[12]

Photometry from the Hipparcos satellite mission showed that DU Crucis varies in brightness with an amplitude of 0.44 magnitudes.^[13] No periodicity could be detected in the variations and it was classified as a slow irregular variable of type Lc, indicating a supergiant.^[4]