Chi² Orionis (Chi² Ori / χ² Orionis / χ² Ori) is a B-type

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 ...

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

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 ...

of Orion. It has an

apparent visual 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 lig ...

of 4.63 but being quite distant, and heavily extinguished it burns with the greatest absolute visual light magnitude among stars in Orion within the near reaches of the galaxy, 0.9 of a magnitude brighter than

Rigel Rigel is a blue supergiant star in the constellation of Orion. It has the Bayer designation β Orionis, which is Latinized to Beta Orionis and abbreviated Beta Ori or β Ori. Rigel is the brightest and most massive componentand ...

. Since 1943, the

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors i ...

of this star has served as one of the stable anchor points by which other stars are classified. It is considered to be a member of the Gemini OB1

association Association may refer to: *Club (organization), an association of two or more people united by a common interest or goal *Trade association, an organization founded and funded by businesses that operate in a specific industry *Voluntary associatio ...

. In apparent brightness it ranks, within Orion, admitting the higher published mean brightness of much more variable stars ranked above it, 35th. Chi¹ Orionis is an unrelated, yellow, main sequence star over two degrees away.

Spectrum

χ² Orionis has a B2

bright supergiant In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

spectrum and is one of the standard B2 Ia stars. It has been reported as having unusually narrow absorption lines and some weak emission lines and was included as one of the original

Be star Be stars are a heterogeneous set of stars with B spectral types and emission lines. A narrower definition, sometimes referred to as ''classical Be stars'', is a non-supergiant B star whose spectrum has, or had at some time, one or more Balmer e ...

s. It is no longer treated as a Be star since many supergiants show some emission features at high resolution and Be stars is usually defined to exclude supergiants.

Variability

χ² Orionis was listed as having likely small amplitude variability in photometry for the Third Catalogue of Stars measured in the Geneva Observatory Photometric System, specifically varying by 22 thousandths of a magnitude. It was included in the

General Catalogue of Variable Stars The General Catalogue of Variable Stars (GCVS) is a list of variable stars. Its first edition, containing 10,820 stars, was published in 1948 by the Academy of Sciences of the USSR and edited by B. V. Kukarkin and P. P. Parenago. Second and thi ...

based on Hipparcos satellite photometry with a magnitude range (in the Hipparchos photometric system) of 4.68 - 4.72 and a period of 2.8 days. A detailed study of the Hipparcos photometry confirmed the star as an α Cyg variable and gave the amplitude of variation as 0.057 magnitudes.

References

{{DEFAULTSORT:Chi2 Orionis Orion (constellation) B-type supergiants Orionis, 62 Orionis, Chi2 041117 028716 Alpha Cygni variables 2135 BD+20 1233