W Crucis is a single-lined eclipsing variable star system 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 first constellati ...

Crux CRUX is a lightweight x86-64 Linux distribution targeted at experienced Linux users and delivered by a tar.gz-based package system with BSD-style initscripts. It is not based on any other Linux distribution. It also utilizes a ports system ...

. It has a spectral class of F8/G1Ia/abe indicating a

yellow supergiant A yellow supergiant (YSG) is a star, generally of spectral type F or G, having a supergiant luminosity class (e.g. Ia or Ib). They are stars that have evolved away from the main sequence, expanding and becoming more luminous. Yellow supergiants ...

with

emission line A spectral line is a weaker or stronger region in an otherwise uniform and continuous spectrum. It may result from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used ...

s in its spectrum. W Crucis varies in brightness between

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

8.18 and 9.01 over a period of 198.5 days. Its

light curve In astronomy, a light curve is a graph (discrete mathematics), graph of the Radiance, light intensity of a celestial object or region as a function of time, typically with the magnitude (astronomy), magnitude of light received on the ''y''-axis ...

has been observed to be asymmetric with subsequent maxima differing in height, which is described as the so-called

O'Connell effect The O'Connell effect is an asymmetry in the photometric light curve of certain close eclipsing binary stars. It was named after the astronomer Daniel Joseph Kelly O'Connell, SJ of Riverview College in New South Wales who in 1951 studied this phen ...

. A secondary minimum is observed when the brightness drops to magnitude 8.5. The shape and duration of the eclipses show that the two stars are

detached A single-family detached home, also called a single-detached dwelling, single-family residence (SFR) or separate house is a free-standing residential building. It is defined in opposition to a multi-family residential dwelling. Definitions ...

and that there is an accretion disk around the primary, more massive, star. Spectral lines can only be seen for one of the stars, a yellow supergiant. The other, more massive, star is hidden within an accretion disk of material stripped from the supergiant. The hidden star has properties that suggest it is a mid-B

main sequence In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...

star. The two are separated by , about . The hot main sequence star has a mass of , while the

supergiant Supergiants are among the most massive and most luminous stars. Supergiant stars occupy the top region of the Hertzsprung–Russell diagram, with absolute visual magnitudes between about −3 and −8. The temperatures of supergiant stars range ...

only has a mass of . The supergiant is deformed by the gravity of the more massive primary star, fills its

Roche lobe In astronomy, the Roche lobe is the region around a star in a binary system within which orbiting material is gravitationally bound to that star. It is an approximately teardrop-shaped region bounded by a critical gravitational equipotential, ...

, and is losing mass. The disk around the hot star is wide and thick, with a temperature at its outer visible edge of . It is the source of the emission lines seen in the spectrum.

References

{{DEFAULTSORT:W Crucis Crux Algol variables Crucis, W B-type main-sequence stars F-type supergiants 059483 105998 Durchmusterung objects G-type supergiants