DL Crucis

DL Crucis is a variable star in the constellation Crux.

DL Crucis

Location of DL Crucis (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Crux
Right ascension	12h 14m 16.9255s[1]
Declination	−64° 24′ 30.662″[1]
Apparent magnitude (V)	6.18[2]
Characteristics
Spectral type	B1.5Ia[3]
U−B color index	−0.73[2]
B−V color index	0.12[2]
Variable type	α Cygni[4]
Astrometry
Radial velocity (Rv)	-10.50[5] km/s
Proper motion (μ)	RA: -5.62[1] mas/yr Dec.: 0.15[1] mas/yr
Parallax (π)	0.80±0.30 mas[6]
Distance	approx. 4,000 ly (approx. 1,300 pc)
Absolute magnitude (MV)	−6.9[7]
Details
Mass	30[3] M☉
Radius	42[7] R☉
Luminosity	251,000[7] L☉
Surface gravity (log g)	2.50[3] cgs
Temperature	20,100[3] K
Rotational velocity (v sin i)	43[3] km/s
Other designations
DL Cru, HIP 59678, HD 106343, CD-63° 732, HR 4653, GSC 08982-04743, CPD-63° 2203, GC 16707, SAO 251803
Database references
SIMBAD	data

Visibility

DL Crucis has a visual apparent magnitude of 6.3 so it is just visible with the unaided eye in dark skies.^[8] It lies in the small southern constellation of Crux, halfway between η Crucis and ζ Crucis and close to the constellation's brightest star α Crucis. This area of sky lies within the Milky Way and close to the Coalsack Nebula.

Properties

DL Crucis has a spectral type of B1.5 Ia, making it a luminous blue supergiant with a temperature over 20,000 K and 251,000 times as luminous as the sun.^[7] It has a radius around 42 times,^[7] and a mass 30 times that of the Sun.^[3]

Variability

A light curve for DL Crucis, plotted from Hipparcos data^[9]

In 1977 DL Crucis, then referred to as HR 4653, was being used as a comparison star to test the variability of δ Crucis. δ Crucis turned out to be constant relative to several other stars, but the difference in brightness between it and HR 4653 changed by 0.02 magnitude.^[10] It was considered likely to be a variable with a period longer than seven hours.^[11]

Hipparcos photometry showed that DL Crucis was varying by up to 0.04 magnitude with a main period of 2 days 21 hours It was classified as an α Cygni variable.^[12] Shortly afterwards it received its variable star designation of DL Crucis.^[13]

A later detailed statistical analysis of the same data found periods of 3.650 and 3.906 days, as well as a first harmonic pulsation, with a maximum brightness range of 0.11 magnitudes.^[7]