Meissa , designated Lambda Orionis (λ Orionis, abbreviated Lambda Ori, λ Ori) is a star in the constellation of Orion. It is a

multiple star A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a ''star cluster'' or ''galaxy'', although, broadly speaking, ...

approximately away with a combined

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's ...

of 3.33. The main components are an O8

giant star A giant star is a star with substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature.Giant star, entry in ''Astronomy Encyclopedia'', ed. Patrick Moore, New York: Oxford University Press ...

and a B-class main sequence star, separated by about 4″. Despite Meissa being more luminous and only slightly further away than Rigel, it appears 3 magnitudes dimmer at visual wavelengths, with much of its radiation emitted in the

ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation ...

due to its high temperature.

Nomenclature

''Lambda Orionis'' is the star's Bayer designation. The traditional name ''Meissa'' derives from the

Arabic Arabic (, ' ; , ' or ) is a Semitic language spoken primarily across the Arab world.Semitic languages: an international handbook / edited by Stefan Weninger; in collaboration with Geoffrey Khan, Michael P. Streck, Janet C. E.Watson; Walter ...

''Al-Maisan'' which means 'The Shining One'. ''Al-Maisan'' was originally used for

Gamma Geminorum Gamma Geminorum (γ Geminorum, abbreviated Gamma Gem, γ Gem), formally named Alhena , is the third-brightest object in the constellation of Gemini. It has an apparent visual magnitude of 1.9, making it easily visible to the naked eye ...

, but was mistakenly applied to Lambda Orionis and the name stuck. In 2016, the

International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...

organized a

Working Group on Star Names The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize proper names for stars for the international astronomical community. It operates under Division C – Education ...

(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 (''Al Haḳʽah'', 'a White Spot'). In

Chinese Chinese can refer to: * Something related to China * Chinese people, people of Chinese nationality, citizenship, and/or ethnicity **''Zhonghua minzu'', the supra-ethnic concept of the Chinese nation ** List of ethnic groups in China, people of ...

, (), meaning '' Turtle Beak'', refers to an asterism consisting of Meissa and both of Phi Orionis Consequently, the

Chinese name Chinese names or Chinese personal names are names used by individuals from Greater China and other parts of the Chinese-speaking world throughout East and Southeast Asia (ESEA). In addition, many names used in Japan, Korea and Vietnam are ofte ...

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

with a stellar classification 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 of around 35,000 K, giving it the characteristic blue glow of a hot

O-type star An O-type star is a hot, blue-white star of spectral type O in the Yerkes classification system employed by astronomers. They have temperatures in excess of 30,000 kelvin (K). Stars of this type have strong absorption lines of ionised helium, ...

. 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. 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 with a companion at an angular separation of 4.41 arcseconds along a

position angle In astronomy, position angle (usually abbreviated PA) is the convention for measuring angles on the sky. The International Astronomical Union defines it as the angle measured relative to the north celestial pole (NCP), turning positive into the ...

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 A B-type main-sequence star (B V) is a main-sequence (hydrogen-burning) star of spectral type B and luminosity class V. These stars have from 2 to 16 times the mass of the Sun and surface temperatures between 10,000 and 30,000 K. B-type stars ...

. There is an outlying component, Meissa C, which is an

F-type main sequence star An F-type main-sequence star (F V) is a main-sequence, hydrogen-fusing star of spectral type F and luminosity class V. These stars have from 1.0 to 1.4 times the mass of the Sun and surface temperatures between 6,000 and 7,600 K.Tables VI ...

with a classification of F8 V. This star in turn may have a very low mass companion that is probably a

brown dwarf 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 ...

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 intense ultraviolet energy being radiated by this star is creating the Sh2-264

H II region An H II region or HII region is a region of interstellar atomic hydrogen that is ionized. It is typically in a molecular cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds ...

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 A Type II supernova (plural: ''supernovae'' or ''supernovas'') results from the rapid collapse and violent explosion of a massive star. A star must have at least 8 times, but no more than 40 to 50 times, the mass of the Sun () to undergo th ...

. Such an event would also explain the star's

peculiar velocity Peculiar motion or peculiar velocity refers to the velocity of an object relative to a ''rest frame'' — usually a frame in which the average velocity of some objects is zero. Galactic astronomy In galactic astronomy, peculiar motion refers to ...

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 A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. w ...

Geminga Geminga is a gamma ray and x-ray pulsar source thought to be a neutron star approximately 250 parsecs (around 800 light-years) from the Sun in the constellation Gemini. Its name, attributed by its discoverer Giovanni Bignami, is both ...

. 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 1879 BD+09 0879