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Theta2 Orionis (θ2 Ori) is a
θ2 Orionis consists of three stars in a line, each about an arc-minute from the next. In addition to the well-known three stars, the
multiple star system
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 ...
in the constellation Orion. It is a few arc minutes from its more famous neighbour the Trapezium Cluster
The Trapezium or Orion Trapezium Cluster, also known by its Bayer designation of Theta1 Orionis, is a tight open cluster of stars in the heart of the Orion Nebula, in the constellation of Orion. It was discovered by Galileo Galilei. On 4 Febru ...
, also known as θ1 Orionis.
Components
θ2 Orionis consists of three stars in a line, each about an arc-minute from the next. In addition to the well-known three stars, the Washington Double Star Catalog
The Washington Double Star Catalog, or WDS, is a catalog of double stars, maintained at the United States Naval Observatory. The catalog contains positions, magnitudes, proper motions and spectral types and has entries for (as of June 2017) 141 ...
confusingly lists a component D which is actually θ1 Orionis C.
There is one other star brighter than 10th magnitude in the region. V1073 Orionis V1, V01 or V-1 can refer to version one (for anything) (e.g., see version control)
V1, V01 or V-1 may also refer to:
In aircraft
* V-1 flying bomb, a World War II German weapon
* V1 speed, the maximum speed at which an aircraft pilot may abor ...
is a B9.5 Orion variable An Orion variable is a variable star which exhibits irregular and eruptive variations in its luminosity and is typically associated with diffuse nebulae. It is thought that these are young stars which will later become regular, non-variable stars o ...
that forms an equilateral triangle with θ2 Ori B and C.
Bizarrely, θ2 Orionis C has a second entry in the Washington Double Star Catalog under the name S490. The companion is 10th magnitude and actually lies between θ2 Ori B and V1073 Ori.
θ1 Orionis, the well known Trapezium cluster, is only 2 arc minutes away from θ2 Orionis A. Despite the names, θ2 Orionis A is marginally brighter than the brightest star in the Trapezium. The Catalog of Components of Double and Multiple Stars
The Catalog of Components of Double and Multiple Stars, or CCDM, is an astrometric star catalogue of double and multiple stars. It was made by Jean Dommanget and Omer Nys at the Royal Observatory of Belgium in order to provide an input catalogue o ...
includes the stars of θ1 and θ2 Ori within the same system of 13 components.
There are dozens of much fainter stars in the same field, many of them 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 ...
s still forming from the Orion molecular cloud complex
The Orion molecular cloud complex (or, simply, the Orion complex) is a star-forming region with stellar ages ranging up to 12 Myr. Two giant molecular clouds are a part of it, Orion A and Orion B. The stars currently forming within the complex a ...
.
Properties
The primary component A appears as a 5th magnitude O classsubgiant
A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution ...
over 100,000 times as luminous as the sun. The spectral type suggests it is evolving away from the 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 ...
, although it is thought to be less than 2 million years old. The spectral peculiarities may be related to close companions or could be caused by the extreme youth of the star.
The 6th magnitude component B is an early B main sequence star nearly 30,000 K and over 10,000 times the luminosity of the sun.
Component C is another B class main sequence star, but cooler and less than a thousand times the luminosity of the sun.
θ2 Orionis A system
θ2 Orionis A is itself atriple 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, ...
system. Its spectral lines were seen to change position periodically, indicating orbital motion. The first orbit was derived in 1924, indicating a period of 21 days. and a rather eccentric orbit.
Speckle interferometry
Speckle imaging describes a range of high-resolution astronomical imaging techniques based on the analysis of large numbers of short exposures that freeze the variation of atmospheric turbulence. They can be divided into the shift-and-add ("''i ...
has resolved a companion about 0.3" away, around 147 AU. High resolution spectroscopy shows that there is an even closer companion, only about 0.47 AU from the primary, for a total of three stars. Both companions are thought to be early A or late B with masses of . This helps to explain the high mass and visual luminosity for an O9.5 star at this distance. The three stars together have nearly the same mass as the O5.5 θ1 Orionis C and visually are even brighter.
θ2 Orionis A also shows unexplained rapidly variable x-ray emission. The x-rays cannot be explained standard mechanisms such as colliding winds or coronal emissions from an unseen companion.
References
{{DEFAULTSORT:Theta2 Orionis Orion (constellation) B-type main-sequence stars Orionis, Theta2 O-type subgiants Orion variables 3 0262351897
Events
January–March
* January 2 – The International Alpha Omicron Pi sorority is founded, in New York City.
* January 4 – A British force is ambushed by Chief Ologbosere, son-in-law of the ruler. This leads to a punit ...
037041
Durchmusterung objects
Orionis, 43
Orionis, V361