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 held together by its gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth make ...

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 Orio ...

in the constellation of Orion. It is about five million years old and roughly away 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 rad ...

. 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 ...

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

to be seen well. It can be seen from both the northern hemisphere 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 ey ...

that has a period of 227.4 million years with an

ellipticity Flattening is a measure of the compression of a circle or sphere along a diameter to form an ellipse or an ellipsoid of revolution (spheroid) respectively. Other terms used are ellipticity, or oblateness. The usual notation for flattening is ...

of 0.06, carrying it as far as from the

Galactic Center The Galactic Center or Galactic Centre is the rotational center, the barycenter, of the Milky Way galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a compact ...

, and as close as . The inclination of the orbit carries it up to away from the

galactic plane The galactic plane is the plane on which the majority of a disk-shaped galaxy's mass lies. The directions perpendicular to the galactic plane point to the galactic poles. In actual usage, the terms ''galactic plane'' and ''galactic poles'' usual ...

. 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 Star formation is the process by which dense regions within molecular clouds in interstellar space, sometimes referred to as "stellar nurseries" or "star-forming regions", collapse and form stars. As a branch of astronomy, star formation include ...

, 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 ide ...

and

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

. 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 re ...

. 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 A pre-main-sequence star (also known as a PMS star and PMS object) is a star in the stage when it has not yet reached the main sequence. Earlier in its life, the object is a protostar that grows by acquiring mass from its surrounding envelope o ...

candidates, which are concentrated in the cluster and nearby regions in an elongated shape. Massive OB stars and

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 ...

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 radiation from hot stars acts on clouds of mater ...

. 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, a ...

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 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