South Gate II（Rigil Kent）, namely alpha Centauri, located inCentaur, is aTriadSystem is the star system closest to the sun.The total apparent magnitude of Nanmen II is about -0.27, the apparent magnitude of Nanmen II A (the brightest of the three stars) is -0.01, and the total absolute magnitude is 4.4. It is used to be the third bright star in the sky.[1]Nanmen Eryin also acts asSouthern crossThe outermost guidance is famous.
The system has three stars, namely, South Gate II A (α Centauri A), South Gate II B (α Centauri B)Adjacent star（Proxima Centauri）。Bilin star is usually considered as a member of this star system. It is only 4.24 light years away from the sun and is the nearest star to the sun.The South Gate II A and B systems are also the first stars (systems) whose parallax is measured.
The angular distance between Bilin Star and South Gate Two AB seen from Earth
The orbit of the South Gate II system can be divided into two parts. One is the system in which the South Gate II A and B revolve around each other, and the other is the orbit of the Bilin star around the South Gate II AB system. This is because the mass of the Bilin star is relatively small, and the distance between the Bilin star and the other two stars is relatively large.
The distance between the South Gate II system and the solar system
The track period of Nanmen II A and B systems is 79.91 years, and the track eccentricity is 0.5179.Their nearest distance is 11.2AU (1.68 billion kilometers), which is about the distance between the sun and Saturn;Their maximum distance is 3.56 AU (5.33 billion km), which is equivalent to the distance between the sun and Pluto.[2]
At first, it was controversial whether Bilin Star had a physical connection with the South Gate II AB system, because there were too few measurements of it.In 2017, an accurate measurement project of its radial velocity was completed, and the results clearly showed that Bilin Star revolved around the Nanmen II AB system, with an orbital period of about 547000 years and an eccentricity of about 0.50 ± 0.08.[3]
Planetary system
Bilin star b
In 2016,European Southern Observatory(ESO) found that there is a rocky planet in Bilin star, which is Bilin star b. It is estimated that the minimum mass is 1.17 times the mass of the earth, the orbital radius is 0.049AU, and it is located in the habitable zone.[4]
Bilin star c
Be linked star c was officially discovered and confirmed in 2020, which may be aSuper EarthOr oneMini Neptune。Its mass is 7 times the mass of the earth, its orbital radius is about 1.49AU, and its revolution period is 1928 days (about 5.28 years).[5-6]
Periplanetary disk
According to the observation results from 2007 to 2012, a study found that the radiation in the 24 µ m (mid/far infrared) band around the Nanmen II AB system was slightly excessive, which may be interpreted as evidence of the existence of sparse periplanetary disks or dense interplanetary dust.It is estimated that the total mass of this disk is 10% of the mass of the moon−7To 10− 6 timesOr 10 to 100 times the mass of clouds in the solar system's ecliptic belt.If there is such a disk around these two stars, the stable disk of South Gate II A may reach 2.8 AU, and that of South Gate II B may reach 2.5 AU.This will make the disc of A completely within the frost line, while a small part of B will be outside.[7]
physical property
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According to star quake analysis, chromospheric activity analysis and gyroscopic chronology research, the age of Nanmen II A and B systems is similar to or older than the sun.Among them, strict star earthquake analysis, different teams have reached at least five different conclusions, and the estimated age is 4.85 ± 0.5 × 10nine[8]Year to 6.52 ± 0.3 × 10nine[9]Years vary.According to chromosphere activity analysis (calcium H&K emission), the conclusion is 4.4 ± 2.1 × 10nineThe result of gyro chronology is 5.0 ± 0.34.4 ± 2.1 × 10nineYears.[10]According to the stellar evolution theory and its mass and spectrum, the ages of Nanmen 2A and B are slightly 5~6 billion years older than the sun[11]
Comparison of the size of stars in the Sun and the Nanmen II system
According to the orbital parameters, the total mass of Nanmen II A and B is about twice the solar mass, and the mass of A and B is 1.09 and 0.92 times the solar mass, respectively.The mass of neighboring stars is very small, only 0.1221 times that of the sun[11]。The radius of South Gate II A is 1.2234 ± 0.0053 times the solar radius, and South Gate II B is 0.8632 ± 0.0037, which is close to the sun, while the radius of the neighboring star is 0.1542 ± 0.0045 times the solar radius, which is much smaller.[26]
The spectral type of Nanmen 2A is G2 V. Similar to the sun, it is a yellow main sequence star.The spectral type of South Gate II B is K1V, which is darker than the sun and is an orange main sequence star.[12]The spectral type of Bilin star is M6 Ve, which is a very dark red dwarf star.The type of magnetic activity on Nanmen 2A is similar to that of the sun, showing the coronal changes caused by the rotation of stars.However, since 2005, its atmospheric activity level has dropped to a very small minimum, which may be similar to the Monde minimum in the history of the sun.Or, it may have a very long period of stellar activity, which is currently in the minimum stage.[13]Although Nanmen 2B is smaller, it emits more energy in X-band.Its light curve changes in a short period, and a flare is observed.Its magnetic field activity is more active than that of Nanmen 2A, with a cycle of 8.2 ± 0.2 years.[14]
Alpha Centauri B is a companion star in the Southern Gate binary system, slightly smaller and darker than the sun.This main sequence star is orange, and its stellar spectrum is classified as K1V.Its mass is about 90% of the sun and its radius is about 86% of the sun.Its star rotation speed is 1.1 ± 0.8 km · s, and its rotation period is about 41 days.Although Alpha Centauri B is darker than Alpha Centauri AX-rayBut it has more energy than A.
Observation history
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Ancient China
The declination of Nanmen'er is low, which is difficult to be observed, but it was also observed in ancient China.《Redords of the Grand History of China·It is recorded in the Tianguan Book that "the south and north stars are called the South Gate." Zhang Shoujie of the Tang Dynasty《Historical record justice》Note: "The two stars of the south gate are located in the south of Kulou, the outer gate of the sky. Zhan: in the Ming Dynasty, the Di and Qiang Tribute; in the dark, the barbarians rebelled; the guest star guarded it, and the foreign troops arrived."[15]Later official history was also transcribed many times.It is said that when Zheng He sailed to the Western Ocean, it was also recorded on the mapSouth GateStar officials are the guiding stars for their navigation.[16]
Ancient West
As early as the second century,Ptolemy In his catalogue, he recorded the South Gate II and its ecliptic coordinates.It is still controversial whether Huang Wei recorded by him is - 44 ° 10 ′ or - 41 ° 10 ′[17](The yellow latitude of J2000 era is - 43.5 °, becauseprecession of the equinoxesThis value has decreased compared with Ptolemy's period).At that time, EgyptAlexandriaSouth Gate II can also be observed, but also because of precession, modern times can no longer do it at the same location.Robert Hues, a British explorer, also recorded the South Gate II in his 1592 book "Tractatus de Globis" and reminded European astronomers.[18]In December 1689, when Jean Richaud was observing a passing comet in Puducherry, he discovered the binary nature of Nanmen 2A and B.South Gate II A and B are successorsSiriusThe second binary system discovered later.[19]
Modern times
South Gate II A and B are largervoluntarilyIt was discovered by Manuel John Johnson when he was observing on St. Helena Island. He told Thomas Henderson of the Royal Observatory of the Cape of Good Hope about this discovery.Later, Henderson determined their parallax based on many accurate position observations of the Nanmen II AB system from April 1832 to May 1833.However, he concealed his research results because he felt that they were too big and doubted that they were untrue.In 1839, Friedrich Wilhelm Bessel published his own accurate measurement in 183861 Cygni Because Henderson's research was not fully recognized at the beginning, Nanmener is sometimes considered as the second star with measured parallax.[20]By 1926, William Stephen Finsen had calculated the approximate values of the orbital elements of Nanmen II A and B systems, which were very close to the values generally accepted in modern times.[21]
In 1915, Robert T. A. Innes discovered the South Gate II C (that is, Bilin Star) by comparing flash photography photos at different times in an investigation of himself.These photos show that the large self motion and parallax of Bilin star are similar to those of Nanmen II A and B in size and direction, which indicates that Bilin star should also be part of that system, and further analysis can find that Bilin star is closer to the sun.
name
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occident
In the West, the traditional name of South Gate II is Rigid Kentaurus, which is usually abbreviated as Rigid Kentarabic“رجل القنطورس”（Rijl al Kentaurus）It means "the feet of centaurs".Another western traditional name of South Gate II is Toliman, which may be fromHebrewOr "ظ م ن ن" in Arabic（Al-Thalimain, meaning ostrich).South Gate 2 is sometimes called Bungula, which may be fromLatinOfungula(meaning "hoof") transformed from.[22-23]
Robert T. A. Innes, who discovered the South Gate II C, proposed to name it Proxima Centaurus, which means "the star closest to the Earth in Centaurus" in Latin.[24]
China
in ChinaTwenty eight nightsIn the system, the second is the south gateCornucopiaPart of the "South Gate", first seen in the Records of the Historian, is considered to be the South Heaven Gate (that is, the south gate of the storeroom).[15]It is said that Zheng He used it to guide his voyages.[16]
Since the South Gate 2C is the closest to the sun, and its Latin name means "the star closest to the Earth in Centaurus", the translator translated it as "a neighbor star", which means "the distance between the sky and the earth is like a neighbor".
Bayer designation
useBayer designation , South Gate II is named Alpha Centauri, and the three stars are Alpha Centauri A, Alpha Centauri B, and Alpha Centauri C.
Future exploration
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Bilin star in the South Gate II system may be the first target for manned or robotic interstellar exploration, because it is the nearest star to the Earth.Using spacecraft technology at the beginning of the 21st century, it will take thousands of years to cross the distance between the sun and neighboring stars, but the possibility of nuclear pulse propulsion or laser sail technology considered in the Breakthrough Starshot program can shorten the flight time to several decades.At the same time, the existence of neighboring star b also provides a goal for it, because the plan aims to go to an exoplanet.[25]
