Omicron Scorpii (ο Sco, ο Scorpii) is a

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

in the

zodiac The zodiac is a belt-shaped region of the sky that extends approximately 8° north and south celestial latitude of the ecliptic – the apparent path of the Sun across the celestial sphere over the course of the year. Within this zodiac ...

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 ...

Scorpius Scorpius is a zodiac constellation located in the Southern celestial hemisphere, where it sits near the center of the Milky Way, between Libra to the west and Sagittarius to the east. Scorpius is an ancient constellation whose recognition pred ...

. With an

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light ca ...

of +4.57, it is visible to the naked eye.

Parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...

measurements indicate a distance of roughly 900

light year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distance, astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by t ...

s. It is located in the proximity of the Rho Ophiuchi dark cloud. This is a white A-type

bright giant A giant star has a substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzspr ...

with a

stellar classification In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction gratin ...

of A4II/III. It is one of the brighter members of this rare class of stars, making it of interest for study. Omicron Scorpii has about eight times the mass of the Sun, fifteen times the radius, and is roughly 40 million years old. The star is radiating around 3,200 times the luminosity of the Sun from its outer atmosphere at an

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of about 8,128 K. It does not display an

infrared excess An infrared excess is a measurement of an astronomical source, typically a star, that in their spectral energy distribution has a greater measured infrared flux than expected by assuming the star is a blackbody radiator. Infrared excesses are of ...

due to circumstellar dust or a possible infrared-bright companion, but the light from this star is subject to

extinction Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

from interstellar dust. This star was originally designated by Lacaille as o Scorpii (lowercase Latin o) instead of omicron, but this designation was reinterpreted as Omicron Scorpii when the star originally designated by Bayer as Omicron Scorpii was reassigned to Libra as

Upsilon Librae Upsilon Librae (υ Lib, υ Librae) is the Bayer designation for a double star in the zodiac constellation Libra. With an apparent visual magnitude of 3.628, it is visible to the naked eye. The distance to this star, based upon an annual pa ...

. Omicron Scorpii was occasionally mentioned as a possible member of the Upper Scorpius sub-group in the Scorpius–Centaurus

OB association The Ob (; ) is a major river in Russia. It is in western Siberia, and with its tributary the Irtysh forms the world's seventh-longest river system, at . The Ob forms at the confluence of the Biya and Katun which have their origins in the Al ...

during the 20th century. However, it does not appear in more recent membership lists for this group due to its small proper motion and small trigonometric parallax as measured by

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 and distances of ...

. This suggests that it is a background star unrelated to Scorpius–Centaurus.

References

{{Stars of Scorpius, state=collapsed A-type bright giants Upper Scorpius Scorpius Scorpii, Omicron Scorpii, 19 147084 080079 6081 Durchmusterung objects