W Crucis is a single-lined eclipsing variable star system in the constellation

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 ...

. 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 dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to identi ...

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 of light intensity of a celestial object or region as a function of time, typically with the magnitude of light received on the y axis and with time on the x axis. The light is usually in a particular frequ ...

has been observed to be asymmetric with subsequent maxima differing in height, which is described as the so-called O'Connell effect. 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 stand-alone house (also called a single-detached dwelling, detached residence or detached house) is a free-standing residential building. It is sometimes referred to as a single-family home, as opposed to a multi-family residential dwelli ...

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 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 temperature range of supergiant stars spa ...

only has a mass of . The supergiant is deformed by the gravity of the more massive primary star, fills its Roche lobe, 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 Objects with variable star designations, Crucis, W B-type main-sequence stars F-type supergiants Hipparcos objects, 059483 Henry Draper Catalogue objects, 105998 Durchmusterung objects G-type supergiants