Pi⁵ Orionis (π⁵ Ori, π⁵ Orionis) is a

binary star A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...

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 ...

Orion Orion may refer to: Common meanings * Orion (constellation), named after the mythical hunter * Orion (mythology), a hunter in Greek mythology Arts and media Fictional entities Characters and species * Orion (character), a DC Comics c ...

. It has 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 3.69, which is bright enough to be visible to the naked eye on a clear night. Based upon an annual parallax shift of 2.43 mas, it is around 1,300

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

s distant from the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

This is a single-lined

spectroscopic binary A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...

star system in a circular orbit with an

orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...

of 3.7005 days. It is an

ellipsoidal variable Rotating ellipsoidal variables are a class of close binary variable star systems whose components are ellipsoidal. They are not eclipsing, but fluctuations in apparent magnitude occur due to changes in the amount of light emitting area visible to ...

, which means the orbit is sufficiently close that the shapes of the components are being distorted by their mutual gravitation. This is causing the visual magnitude of the system to vary regularly by 0^m.05 over the course of each orbit, as the orientation of the stars change with respect to the Earth. Detailed analysis of the

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 ...

suggests that the primary star is also pulsating and is probably a

Slowly pulsating B-type star A slowly pulsating B-type star (SPB), formerly known as a 53 Persei variable, is a type of pulsating variable star. They may also be termed a long-period pulsating B star (LPB). As the name implies, they are main-sequence stars of spectral type B2 ...

. The primary component is a B-type

giant star 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 Hertzsp ...

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 B2 III. It is only about 16 million years old and spins with a

projected rotational velocity Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface. The rotation of a star produces an equatorial bu ...

of 90 km/s. Despite the spectral class, the primary star is thought to be at or near the end of its main sequence evolution. It has about 12.5 times the

mass of the Sun The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies a ...

and radiates 11,262 times the

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

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 . The secondary star is not detectable clearly, but modelling of the brightness variations and orbit suggest that it is a

main sequence star Main may refer to: Geography *Main River (disambiguation), multiple rivers with the same name *Ma'in, an ancient kingdom in modern-day Yemen * Main, Iran, a village in Fars Province * Spanish Main, the Caribbean coasts of mainland Spanish terri ...

with a spectral class of about B6. It is smaller, cooler, and much less luminous than the primary, and orbits at about 26

astronomical unit The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its m ...

References

External links

* {{DEFAULTSORT:Pi5 Orionis B-type giants Rotating ellipsoidal variables Spectroscopic binaries Orion (constellation) Orionis, Pi5 Durchmusterung objects Orionis, 08 031237 022797

1567 Year 1567 ( MDLXVII) was a common year starting on Wednesday of the Julian calendar. Events January–March * January 20 – Battle of Rio de Janeiro: Portuguese forces under the command of Estácio de Sá definitively drive the F ...