25 Orionis, less commonly known by its Bayer designation

Bayer designation

A Bayer designation is a stellar designation in which a specific star is identified by a Greek letter, followed by the genitive form of its parent constellation's Latin name...

 Psi¹ Orionis (Ψ¹ Orionis, Ψ¹ Ori) is a fifth-magnitude star

Star

A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...

 in the constellation

Constellation

In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

 Orion

Orion (constellation)

Orion, often referred to as The Hunter, is a prominent constellation located on the celestial equator and visible throughout the world. It is one of the most conspicuous, and most recognizable constellations in the night sky...

. Its kinematics place it among a dense cluster

Star cluster

Star clusters or star clouds are groups of stars. Two types of star clusters can be distinguished: globular clusters are tight groups of hundreds of thousands of very old stars which are gravitationally bound, while open clusters, more loosely clustered groups of stars, generally contain less than...

 of almost 200 low-mass pre-main-sequence stars in the Orion OB1a

Orion OB1 Association

The Orion OB1 stellar association is a contingent group of several dozen hot giant stars of spectral types O and B. Associated are thousands of lower-mass stars, and a number of protostars. It is part of the larger Orion Molecular Cloud Complex...

 subassociation known as the 25 Orionis group.

Properties

Like the star Pleione

Pleione (star)

Pleione is a binary star in the Pleiades star cluster , located roughly 390 light years away in the constellation of Taurus. Pleione was not given a Bayer designation, but did receive a Flamsteed number—hence its designation 28 Tauri...

 in the Pleiades

Pleiades (star cluster)

In astronomy, the Pleiades, or Seven Sisters , is an open star cluster containing middle-aged hot B-type stars located in the constellation of Taurus. It is among the nearest star clusters to Earth and is the cluster most obvious to the naked eye in the night sky...

 open cluster

Open cluster

An open cluster is a group of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way Galaxy, and many more are thought to exist...

, 25 Ori is a Be star

Be star

A Be star is a B-type star with prominent emission lines of hydrogen in its spectrum. The designation is combined by the spectral class, B, and the lowercase e denoting emission in the spectral classification system. Line emission from other atomic ions might be present as well, but is typically...

 with a gaseous circumstellar disk

Circumstellar disk

A circumstellar disk is a torus, pancake or ring-shaped accumulation of matter composed of gas, dust, planetesimals, asteroids or collision fragments in orbit around a star. Around the youngest stars, they are the reservoirs of material out of which planets may form...

. The SIMBAD

SIMBAD

SIMBAD is an astronomical database of objects beyond the Solar System...

 astronomical database lists its spectral class

Stellar classification

In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...

 as B1Vpe. The suffix "pe" refers to "Emission lines with peculiarity", a classification typical of many Be stars whose peculiar emissions come from the gaseous equatorial disks formed of material ejected from the star.

25 Orionis is a fast rotator, clocking a rotational velocity of 316 km/s, significantly faster than Achernar

Achernar

Achernar , sometimes spelled Achenar, is the brightest star in the constellation Eridanus and the ninth-brightest star in the night sky. Of the top ten apparent brightest stars —Sirius, Canopus, Alpha Centauri, Arcturus, Vega, Capella, Rigel, Procyon, Achernar and Betelgeuse—Achernar is the hottest...

's speed of 251 km/s in the constellation Eridanus

Eridanus (constellation)

Eridanus is a constellation. It is represented as a river; its name is the Ancient Greek name for the Po River. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations. It is the sixth largest of the modern...

. Having a radius of 6R_☉, the star rotates on its axis roughly once every 23 hours. With a mass in excess of 10M_☉

Solar mass

The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...

, the star is expected to explode as a supernova

Supernova

A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...

.

See also

• Lists of stars in the constellation Orion
• Class B Stars
• Be stars
• Shell star
  Shell star
  A shell star, also termed Gamma Cassiopeiae variable , is a star having a spectrum that exhibits features indicating a circumstellar disc of gas surrounding the star at the equator. They exhibit irregular variations in their luminosity due to the outflow of matter...
  
  
• Circumstellar disk
  Circumstellar disk
  A circumstellar disk is a torus, pancake or ring-shaped accumulation of matter composed of gas, dust, planetesimals, asteroids or collision fragments in orbit around a star. Around the youngest stars, they are the reservoirs of material out of which planets may form...
  
  

External links

• Jim Kaler's Stars, University of Illinois: 25 ORI (25 Orionis)
• Philippe Stee's in-depth information on: Hot and Active Stars Research
• Olivier Thizy's in-depth information on: Be Stars