DL Crucis is a variable star in the constellation Crux.
  | |
| 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 | |
| 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
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]