The Lambda Orionis Cluster (also known as the Collinder 69) is an open

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 ...

cluster located north-west of the star

Betelgeuse Betelgeuse is a red supergiant of spectral type M1-2 and one of the largest stars visible to the naked eye. It is usually the tenth-brightest star in the night sky and, after Rigel, the second-brightest in the constellation of Orion ...

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 is about five million years old and roughly away from the Sun. Included within the cluster is a

double star In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes. This occurs because the pair either forms a binary star (i.e. a bi ...

named

Meissa Meissa , designated Lambda Orionis (λ Orionis, abbreviated Lambda Ori, λ Ori) is a star in the constellation of Orion. It is a multiple star approximately away with a combined apparent magnitude of 3.33. The main components are ...

. With the rest of Orion, it is visible from the middle of August in the morning sky, to late April before Orion becomes too close to the Sun to be seen well. It can be seen from both the

northern hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...

and the southern hemisphere.

Description

The cluster is following an orbit through the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...

that has a period of 227.4 million years with an ellipticity of 0.06, carrying it as far as from the Galactic Center, and as close as . The inclination of the orbit carries it up to away from the galactic plane. On average it crosses the plane every 33.3 million years. The star cluster is young and contains a large number of low-mass stars, some

T Tauri stars T Tauri stars (TTS) are a class of variable stars that are less than about ten million years old. This class is named after the prototype, T Tauri, a young star in the Taurus star-forming region. They are found near molecular clouds and iden ...

and

brown dwarfs Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most m ...

. One notable member is LOri167, which is a wide binary consisting of a potential

planetary-mass object A planetary-mass object (PMO), planemo, or planetary body is by geophysical definition of celestial objects any celestial object massive enough to achieve hydrostatic equilibrium (to be rounded under its own gravity), but not enough to sustain ...

and a brown dwarf. Observations of the star cluster with the

Spitzer Space Telescope The Spitzer Space Telescope, formerly the Space Infrared Telescope Facility (SIRTF), was an infrared space telescope launched in 2003. Operations ended on 30 January 2020. Spitzer was the third space telescope dedicated to infrared astronomy, f ...

have shown that 25% of the low-mass stars and 40% of the

substellar objects A substellar object, sometimes called a substar, is an astronomical object the mass of which is smaller than the smallest mass at which hydrogen fusion can be sustained (approximately 0.08 solar masses). This definition includes brown dwarfs and fo ...

are surrounded by a

circumstellar disk A circumstellar disc (or circumstellar disk) is a torus, pancake or ring-shaped accretion disk of matter composed of gas, dust, planetesimals, asteroids, or collision fragments in orbit around a star. Around the youngest stars, they are the rese ...

. Two of these being actively photoevaporated by Meissa.

Molecular ring and cluster evolution

The cluster might have formed in the central region of an elongated cloud, which is supported by the distribution of pre-main-sequence star candidates, which are concentrated in the cluster and nearby regions in an elongated shape. Massive OB stars and low-mass stars formed in the central regions of these clouds. The low-mass stars closest to the massive stars likely lost their

circumstellar disks A circumstellar disc (or circumstellar disk) is a torus, pancake or ring-shaped accretion disk of matter composed of gas, dust, planetesimals, asteroids, or collision fragments in orbit around a star. Around the youngest stars, they are the re ...

due to

photoevaporation Photoevaporation denotes the process where energetic radiation ionises gas and causes it to disperse away from the ionising source. This typically refers to an astrophysical context where ultraviolet electromagnetic radiation, radiation from hot st ...

. Many low-mass stars

parsecs The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, an ...

away were unaffected by this and represent the current population of low-mass stars with a circumstellar disk. The cluster is surrounded by a large molecular ring, called the Lambda Orionis ring. This was interpreted as a remnant of a

supernova A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...

that exploded one million years ago. The supernova blast encountered the clouds and gas in the region and the blast dispersed the parent core, creating the molecular ring.

References

* Sky Atlas 2000.0 Second Edition

External links

* {{Portal bar, Astronomy, Stars, Spaceflight, Outer space, Solar System Orion (constellation) Open clusters

Description

Molecular ring and cluster evolution

See also

References

External links