θ Carinae, Latinized as Theta Carinae, is a spectroscopic binary star in the southern constellation of

Carina Carina may refer to: Places Australia * Carina, Queensland, a suburb in Brisbane * Carina Heights, Queensland, a suburb in Brisbane * Carina, Victoria, a locality in Mildura Serbia * Carina, Osečina, a village in the Kolubara District ...

. With an

apparent visual 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 lig ...

of 2.76, it is the brightest star in the

open star cluster An open cluster is a type of star cluster made of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...

IC 2602 IC 2602 (also known as the Southern Pleiades, Theta Carinae Cluster, or Caldwell 102) is an open cluster in the constellation Carina. Discovered by Abbe Lacaille in 1751 from South Africa, the cluster is easily visible to the unaided eye, and is on ...

. It marks the northeastern end of the

Diamond Cross Carina ( ) is a constellation in the southern sky. Its name is Latin for the keel of a ship, and it was the southern foundation of the larger constellation of Argo Navis (the ship ''Argo'') until it was divided into three pieces, the other two be ...

asterism. Parallax measurements from the Hipparcos mission place this star at a distance of about from Earth.

Properties

The MKK stellar classification of this star is B0.5 Vp, which indicates this

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 ...

generates energy through the

nuclear fusion Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles ( neutrons or protons). The difference in mass between the reactants and products is manife ...

of hydrogen in its core. The 'p' suffix designates peculiar spectral features, which have been observed in both optical and ultraviolet wavelengths. Theta Carinae is a single-lined spectroscopic binary with a 2.2 day period; the shortest known orbital period among massive stars, suggesting earlier mass transfer between the two components, possibly explaining the spectral peculiarities. In this spectroscopic system, the primary star is probably a

blue straggler A blue straggler is a main-sequence star in an open or globular cluster that is more luminous and bluer than stars at the main sequence turnoff point for the cluster. Blue stragglers were first discovered by Allan Sandage in 1953 while perform ...

, which is an unusual type of star created by merging or the interaction between two or more stars. The source of the mass transfer is likely to be the less massive secondary companion, and what is now is the primary star was probably originally the less massive component. The estimated age of the pair is 4 million years, and it appears much younger than the surrounding IC 2602 cluster. The primary star is about 15 solar masses () and five

solar radii Solar radius is a unit of distance used to express the size of stars in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: :1\,R_ = 6.957\tim ...

(). Theta Carinae has an intensely hot outer radiating envelope with an effective surface temperature of 31,000 K. Once the primary reaches around 11 million years old, the star will expand and will begin to transferring its outer surface mass back to its companion. Little is known about the companion star, but it is likely an

F-type 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 VII ...

with a luminosity less than 1% of the primary.

Etymology

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 '' Southern Boat'', refers to an asterism consisting of θ Carinae,

V337 Carinae V337 Carinae (V337 Car, q Carinae) is a K-type bright giant star in the constellation of Carina. It is an irregular variable and has an apparent visual magnitude which varies between 3.36 and 3.44. V337 has a spectral cla ...

PP Carinae p Carinae is the Bayer designation of a star in the southern constellation of Carina. It has the variable star designation PP Carinae and, at an apparent visual magnitude of +3.3, is readily visible to the naked eye from the southern hem ...

, β Carinae and ω Carinae. Consequently, θ Carinae itself is known as (, en, the Third Star of Southern Boat).AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 28 日
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Apparent location

In most versions of its asterism, the neighbouring bright stars, thus plotted along the imaginary hull forming Carina are

Omega Carinae Omega Carinae, Latinized from ω Carinae, is a star in the constellation Carina. With a declination greater than 70 degrees south of the celestial equator, it is the most southerly of the bright stars of Carina (third-magnitude or brig ...

which is approximately 120 light years closer and PP (also known as p) Carinae, of a similar distance to Theta.

References

External links

Southern Sky Photos
{{DEFAULTSORT:Theta Carinae B-type main-sequence stars Blue stragglers Carinae, Theta Carina (constellation) 4199 093030 052419 Durchmusterung objects IC 2602 Spectroscopic binaries