Meissa , designated Lambda Orionis (λ Orionis, abbreviated Lambda Ori, λ Ori) is a

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 ...

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 a multiple star approximately away with a combined apparent magnitude of 3.33. The main components are an O8 giant star and a B-class

main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...

star, separated by about 4″. Despite Meissa being more

luminous Luminous may refer to: * Luminous flame, a flame emitting visible light Music * Luminous (group), a South Korean boy band * ''Luminous'' (EP), an EP by Cesium 137 * ''Luminous'' (John Hicks and Elise Wood album), 1985–88 * Luminous (The Hor ...

and only slightly further away than Rigel, it appears 3 magnitudes dimmer at visual wavelengths, with much of its radiation emitted in the ultraviolet due to its high temperature.

Nomenclature

''Lambda Orionis'' is the star's

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars. ...

. The traditional name ''Meissa'' derives from the Arabic ''Al-Maisan'' which means 'The Shining One'. ''Al-Maisan'' was originally used for Gamma Geminorum, but was mistakenly applied to Lambda Orionis and the name stuck. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included ''Meissa'' for this star. It is now so entered in the IAU Catalog of Star Names. The original Arabic name for this star, ''Al Hakah'' (the source for another name for it, ''Heka'') refers to the Arabic lunar mansion that includes this star and the two of

Phi Orionis Phi (; uppercase Φ, lowercase φ or ϕ; grc, ϕεῖ ''pheî'' ; Modern Greek: ''fi'' ) is the 21st letter of the Greek alphabet. In Archaic and Classical Greek (c. 9th century BC to 4th century BC), it represented an aspirated voicele ...

(''Al Haḳʽah'', 'a White Spot'). In Chinese, (), meaning '' Turtle Beak'', refers to an asterism consisting of Meissa and both of

Consequently, the Chinese name for Meissa itself is (, en, the First Star of Turtle Beak.)
AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 24 日
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Properties

Meissa is a giant star 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 grati ...

of O8 III and an apparent visible magnitude 3.54. It is an enormous star with about 26-28 times the mass of the Sun and 10-13 times the Sun's radius. The outer atmosphere has 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 around 35,000 K, giving it the characteristic blue glow of a hot O-type star. Meissa is a soft X-ray source with a luminosity of 10³² erg s⁻¹ and peak emission in the energy range of 0.2–0.3 keV, which suggests the X-rays are probably being generated by the

stellar wind A stellar wind is a flow of gas ejected from the upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spherically symmetric. D ...

. The stellar wind of Meissa is well characterized by a mass-loss rate of solar masses per year and a terminal velocity of . Meissa is actually 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 ...

with a companion at an

angular separation Angular distance \theta (also known as angular separation, apparent distance, or apparent separation) is the angle between the two sightlines, or between two point objects as viewed from an observer. Angular distance appears in mathematics (in pa ...

of 4.41

arcsecond A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...

s along a position angle of 43.12° (as of 1937). This fainter component is of magnitude 5.61 and it has a stellar classification of B0 V, making it a B-type main sequence star. There is an outlying component, Meissa C, which is an F-type main sequence star with a classification of F8 V. This star in turn may have a very low mass companion that is probably a brown dwarf.

Ring

Meissa is surrounded by a ring of nebulosity about 12 degrees across. It is thought to be the remains of a supernova explosion, now ionized by the ultraviolet radiation from Meissa itself and some of the surrounding hot stars.

Cluster

This star is the dominant member of a 5-million-year-old star-forming region known as the λ Orionis cluster, or

Collinder 69 The Lambda Orionis Cluster (also known as the Collinder 69) is an open star cluster located north-west of the star Betelgeuse in the constellation of Orion. It is about five million years old and roughly away from the Sun. Included within the clu ...

. The intense ultraviolet energy being radiated by this star is creating the

Sh2-264 Sharpless 264, also known as the Lambda Orionis Ring, is a molecular cloud and H II region, which can be seen in the northern region of the Orion molecular cloud complex (OMCC), in the constellation of Orion. The OMCC is one of the best-known sta ...

H II region in the neighboring volume of space, which in turn is surrounded by an expanding ring of cool gas that has an age of about 2–6 million years. The expansion of this gaseous ring may be explained by a former binary companion of Meissa that became a Type II supernova. Such an event would also explain the star's peculiar velocity with respect to the center of the expanding ring, as the explosion and resulting mass loss could have kicked Meissa out of the system. A potential candidate for the supernova remnant is the neutron star Geminga. However, the last is unlikely given the distance between Geminga and the cluster.

References

{{DEFAULTSORT:Meissa Orionis, Lambda Orionis, 39 Orion molecular cloud complex O-type giants B-type main-sequence stars Binary stars 036861 026207 Orion (constellation) Stars named from the Arabic language Emission-line stars

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