Omicron¹ Orionis (ο¹ Ori) is a binary star in the northeastern corner of the constellation Orion. It is visible to the naked eye with 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 4.7. Based upon an annual parallax shift of , it is located approximately 650 light years from the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

. At that distance, the visual magnitude of the star is diminished by an interstellar absorption factor of 0.27 due to intervening dust. Omicron1OriLightCurve

The two components of this system have an orbital period of greater than 1,900 days (5.2 years). The primary component is an

evolved Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

red giant with the stellar classification of M3S III. This is an

S-type star An S-type star (or just S star) is a cool giant with approximately equal quantities of carbon and oxygen in its atmosphere. The class was originally defined in 1922 by Paul Merrill for stars with unusual absorption lines and molecular bands no ...

on the asymptotic giant branch. It is a

semiregular variable In astronomy, a semiregular variable star, a type of variable star, is a giant or supergiant of intermediate and late (cooler) spectral type showing considerable periodicity in its light changes, accompanied or sometimes interrupted by various irre ...

that is pulsating with periods of 30.8 and 70.7 days, each with nearly identical

amplitude The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of am ...

s of 0.05 in magnitude. The star has an estimated 90% of the mass of the Sun but has expanded to 214 times the Sun's radius. It shines with 4,046 times the

solar luminosity The solar luminosity (), is a unit of radiant flux ( power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun. One nominal ...

from its outer atmosphere at an effective temperature of 3,465 K.

References

{{DEFAULTSORT:Omicron1 Orionis M-type giants S-type stars Asymptotic-giant-branch stars Orion (constellation) Orionis, Omicron1 Orionis, 04 030959 022667

1556 __NOTOC__ Year 1556 ( MDLVI) was a leap year starting on Wednesday (link will display the full calendar) of the Julian calendar. Events January–June * January 16 – Charles V, having already abdicated as Holy Roman Emperor, ...

Semiregular variable stars Binary stars Durchmusterung objects