DL Crucis is a

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Crux 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 c ...

Visibility

DL Crucis has a visual

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

of 6.3 so it is just visible with the unaided eye in dark skies. 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 Acrux is the brightest star in the southern constellation of Crux. It has the Bayer designation α Crucis, which is Latinised to Alpha Crucis and abbreviated Alpha Cru or α Cru. With a combined visual magnitude of +0.76, it is the 13 ...

. This area of sky lies within the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...

and close to the

Coalsack Nebula The Coalsack Nebula (Southern Coalsack, or simply the Coalsack) is a prominent dark nebula in the skies, being easily visible to the naked eye as a dark patch obscuring a brief section of Milky Way stars as they cross their southernmost region of ...

Properties

DL Crucis has a spectral type of B1.5 Ia, making it a luminous

blue supergiant A blue supergiant (BSG) is a hot, luminous star, often referred to as an OB supergiant. They have luminosity class I and spectral class B9 or earlier. Blue supergiants are found towards the top left of the Hertzsprung–Russell diagram, above an ...

with a temperature over 20,000 K and 251,000 times as luminous as the sun. It has a radius around 42 times, and a mass 30 times that of the Sun.

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 Delta Crucis or δ Crucis, also identified as Imai (), is a star in the southern constellation of Crux, and is the faintest of the four bright stars that form the prominent asterism known as the Southern Cross. This star has an apparent ...

. 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. It was considered likely to be a variable with a period longer than seven hours.

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial obj ...

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 Alpha Cygni variables are variable stars which exhibit non-radial pulsations, meaning that some portions of the stellar surface are contracting at the same time other parts expand. They are supergiant stars of spectral types B or A. Variations in ...

. Shortly afterwards it received its

variable star designation In astronomy, a variable star designation is a unique identifier given to variable stars. It uses a variation on the Bayer designation format, with an identifying label (as described below) preceding the Latin genitive of the name of the constell ...

of DL Crucis. 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.

References

{{DEFAULTSORT:DL Crucis Crux Alpha Cygni variables B-type supergiants Crucis, DL 106343 4653 Durchmusterung objects 059678