Cross II

fixed star

Cross Two Southern cross The brightest star in the sky is also the 13th brightest star in the night sky, with an apparent magnitude of 0.77. It is called Acrux (Cru α) in the West. Cross II, alpha star of Southern Cross, is a binary star composed of two stars with apparent magnitude of 1.39 and 2.09, with composite magnitude of 0.77 and absolute magnitude of -3.77. Ranked 13th in the bright star list. It is composed of B0.5IV sub star and B1V sub star, with a distance of 5.6 ″ and a distance of 320 light-years from the Earth. Portugal called Cross II "Magellan Star" to commemorate the first explorer who sailed around the world.

Chinese name: Cross II
Constellations: Southern cross
Right ascension: 12:26:36s
Declination: About - 63 ° 05 ′ 56.73 ″

Western name: Acrux（Cru α）
Apparent magnitude: 1.39 & 2.09
Centennial cycle of right ascension: -0.358″
Centennial declination: -1.23″
Composite magnitude: zero point seven seven

catalog

position

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The center of the Southern Cross is about South Latitude 60 °, so the Tropic of Cancer To the south, you can see the constellation completely. ancient India Some astronomers call it Tri shanku, an ancient India Sanskrit Also on behalf of auspicious Swastika （ Swastika ）Stands for the Southern Cross. In Sanskrit, Dhruva means very stable. It was originally used as a form of address Polaris , and Tri shanku means unstable, or a very bad fairy tale. This word is used in Sanskrit in India to refer to the Southern Cross as a metaphor for its elusive movement. In fact, Cross 2 is just a star in the Southern Cross, which is the southernmost bright star in the constellation Centaur South Gate Two（ Alpha Centauri ）More to the south.

Astrometry

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Radial speed (Rv)	- 11240 m/s
Right ascension direction of self (μ 1)	- 35.37 mas/yr
Self declination direction (μ 2)	- 4.73 mas/yr
Parallax (π)	10.13±0.50 mas
distance	320±20 l.y
Compound apparent magnitude	zero point seven seven
Absolute apparent magnitude	-3.77

Cross II

characteristic

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Spectrum and Photometric Type	B0.5IV & B1V
B-V color index	-0.26
U-B color index	-0.03

representative

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Cross 2 is one of the five stars in the Southern Cross on the Australian flag and one of the four stars in the Southern Cross on the New Zealand flag. It is also in the Southern Cross on the Brazilian flag. The 26 stars on the Brazilian flag represent a state in decibels, and Cross 2 represents a state in decibels Sao Paulo 。

distance

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Cross II is a trinity star system 320 light-years away from the solar system, but only two stars can be distinguished by visual observation. The distance between α 1 and α 2 is only 4 arc seconds. The luminosity of α 1 is 1.40, and α 2 is 2.09. Both stars are high temperature B-type star (near O star ）The surface temperature is 28000K and 26000K respectively, and the individual brightness is 25000 and 16000 times of the sun. The orbital periods of α 1 and α 2 are very long, which makes these two stars seem almost stationary. It is estimated that the minimum distance between the two stars is only 430 astronomical units, and the orbital period is 1500 years long, and may be even longer.

Cross II itself is still a Spectral binary The mass of the two stars is 14 and 10 times that of the sun respectively, and they circle each other at a distance of 1 astronomical unit in a period of 76 days. The mass of α 1 and bright companion star α 2 indicates that they may become supernovae one day. α2， That is, the darker companion star may become a massive neutron star for the rest of its life.

Type B with a distance of 90 arc seconds from the cross triad star system Subgiant , which may have a gravitational effect on Cross II. However, if he is really near Cross II Spectrum type , the light is too dim. So he might just be a Optical binary , the distance from the solar system may be twice that of Cross II, that is, the distance from Cross II Solar system from the cross II It's almost far.

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