Alpha Centauri

Alpha Centauri / α Centauri / α Cen, also known as Rigil Kentaurus, Rigel Kent, or Toliman, is the brightest star in the southern constellation of Centaurus and an established binary star system, Alpha Centauri AB (α Cen AB). It appears to the naked-eye as the third brightest star in the entire night sky, being only outshone by Sirius and Canopus. By total visual magnitude Alpha Centauri AB is −0.27, which is just fractionally brighter than the fourth brightest individual star in the night sky, Arcturus.

In the southern hemisphere Rigel Kent is known as one of The Pointers, along with Beta Centauri or Agena / Hadar, as both stars directly point towards the constellation Crux - the Southern Cross. The Pointers were so named because they easily distinguish the true Southern Cross from the asterism known as the False Cross. The star Beta Centauri lies some 4.4 degrees further west from Alpha Centauri, mid-way between the Southern Cross and α Centauri. Both stars are too far south to be visible for most northern hemisphere observers.

Those that can see α Centauri will find it lying close to the southern horizon during their northern summer. From south of about -33 degrees latitude, α Centauri is circumpolar and never sets below the horizon.

Alpha Centauri has the primary distinction of being the closest of all the stars visible to the naked eye in the night sky. Its distance is about 1.3 parsecs, or 4.37 light years.

Nature of Alpha Centauri

Alpha Centauri is a triple star system. The brightest two stars make a close orbiting binary; an additional much more distant and fainter companion is called Proxima Centauri, Proxima or α Cen C. Individually, the two bright stars rate, respectively, as the fourth and twenty-first brightest stars in the sky (excluding the Sun).

Observationally, α Centauri AB is too close to be resolved by the naked eye. However, for more than two centuries it has been very well observed and measured by telescopes as small as 5 cm in aperture.

Observational History of Alpha Centauri

Its duplicity, according to the renowned double star observer Robert Aitken (1961), and as now stated in the 6th Catalog of Binary Stars (2008), was originally discovered in December 1689 by Father Richaud from the city of Pondicherry in India while he was observing a comet. Sir John Herschel in 1834 was then the first to make micrometrical observations, though astrometric positions were made as early as 1752 by Abbé Nicolas Louis de Lacaillé using a meridian circle. Since the early 20th Century, measures have been made with photographic plates.

By 1926, William Stephen Finsen produced the general orbit elements now accepted for this system. Future positions could then be calculated from a binary star ephemeris with sufficiently accuracy for visual observers. Others (e.g. the French astronomer D. Pourbaix in 2002) have slightly refined the orbital elements. (See the second Visual binary orbit in the Observational data side-box.) The established eighty-odd year orbital period for α Centauri AB is therefore reasonably accurate.

Alpha Centauri is popularly known as the closest star system to our Solar System at about 4.37 light-years distant, or about 41.5 trillion kilometres, 25.8 trillion miles or 277,600 AU. This was discovered by Thomas Henderson, who made many exacting observations of both stars in the AB system. He obtained their trigonometric parallaxes (their tiny annual circular movements against the background stars) between April 1832 and May 1833, but did not release them because he seriously doubted his own results, feeling they were too large to be true. Henderson eventually published his results in 1839, after Friedrich Wilhelm Bessel had released his own accurately determined parallax for the star 61 Cygni in 1838. For this reason, Alpha Centauri is considered to be the second star to have its distance measured.

Proxima Centauri was discovered by R.T.A. Innes in 1915 from South Africa, being detected by blinking two separate photographic plates taken at different times during one of his dedicated proper motion surveys. It showed very large proper motions similar in both size and direction to those of α Centauri AB, which suggested they were associated. It is usually regarded as part of the system, and presently in its orbit is slightly closer to us than α Centauri AB. Lying 4.22 light-years away, Proxima Centauri is thus celebrated as the closest star to the Sun. Most of the modern calculated distances for all three stars are derived from the parallaxes in the Hipparcos star catalog (HIP).

Alpha Centauri : The Gravitational System

Alpha Centauri is the collective name of this triple star system. It consists of two main stars, α Cen A and α Cen B, together often labelled as α Cen AB, which is the established binary star system. A third component, α Cen C is the much smaller and dimmer red dwarf star named Proxima Centauri.

The designation as "AB" has important significance for binary stars. In double star astronomy, and in most astronomical references, this suggests the central gravitational point of the binary relative to companion star(s) in multiple systems.^[7] "AB-C" usage refers to the orbit of Proxima around the central binary, being the distance between the centre of gravity and the outlying companion. Sometimes older references use A×B, but this usage has been discontinued for decades. Since the distance from the Sun to α Cen AB does not differ significantly from that to either star in the binary system, it makes sense to refer to the binary as a solitary object.

These binary components and Proxima Centauri are described individually as follows;

Alpha Centauri AB

Alpha Centauri A is the principal member or primary of the binary system, being both slightly larger and more luminous than our Sun. Like the Sun, it is a main sequence star with a similar yellowish-white colour, whose stellar classification is spectral type G2 V. From the determined mutual orbital parameters, Alpha Centauri A is about 10% more massive than our Sun, with a radius about 23% larger.^[3]

Alpha Centauri B is the companion star or secondary to the primary star, appearing slightly smaller and less luminous than the Sun. This main sequence star displays the spectral type of K1 V, being an observed deeper orangish-yellow colour than the primary star. By mass, α Cen B is about 90% of the Sun, and is 14% smaller in radius.^[3] A likely solar-like rotation period of some 36.8 days has been determined.^[8] Although it has a lower luminosity than component A, star B emits a higher level of energy in the X-ray part of the spectrum. The light curve of B varies on a short time scale and at least one flare has been observed.^[9]

The stars revolve about each other in a moderately elliptical (e = 0.5179) 79.91-year-long orbit.^[10] Unlike most of the planetary orbits in the Solar System, these stars can approach to 11.2 astronomical units (1.67 billion kilometres - roughly the distance between the Sun and Saturn) of each other, or can recede to a separation of 35.6 AU (5.9 billion kilometres, or approximately the distance from the Sun to Pluto). [1] From this one can calculate the total mass (ΣM_ʘ) of both stars to be about twice that of the Sun (

[(11.2 + 35.6) / 2] 3 / 79.91 2 = 2.0

, see formula). Both these stars, according to stellar evolution theory, are slightly older than the Sun^[3]; some sources quote 5 to 6 billion years (as implied by their derived mass and spectral characteristics).

In their true orbit, both stars last made their closest approach (periastron) of 11.5 A.U. in August 1955; this will not occur again until May 2035. Apastron, when the stars are furthest apart in the orbit at 35.6 A.U., last occurred in May 1995. The two stars are presently approaching each other. The next apastron will be in A.D. 2075. ^[10]

As seen from the Earth, the apparent orbit of this binary star means that the separation and position angle are in continuous change throughout the projected eighty-odd year period. According to the current version of the U.S.N.O.'s 6th Binary Star Catalogue : Ephemeris, the observed distance between the stars is now 8.29 arcsec through P.A. 237 degrees (2008) reducing in the next year to 7.53 arcsec through P.A. 241 degrees (2009). The next apparent closest approach of both these stars will be seen during February 2016, when the distance reduces to 4.0 arcsec through P.A. 300 degrees. (See External Reference. ) The maximum separation of these stars is about 22 arcsec, which last happened in February 1976. This will not occur again until January 2056.

Alpha Centauri C / Proxima Centauri / V645 Centauri

The much fainter red dwarf star named Alpha Centauri C, "α Cen C", Proxima Centauri, or simply "Proxima", is about 13,000 A.U. away from Alpha Centauri AB (1.94 trillion kilometres or 0.21 ly – about one-twentieth the distance between Alpha Centauri AB and the Sun). It may be in orbit around it, though the period must be in the order of 100,000 to 500,000 years or more. It is possible that the orbit might be hyperbolic, similar to the planetary sling-shot effect adopted by interplanetary spacecraft to change direction and velocity to a second planetary body, and so Proxima may leave the system after a few million years. Association with Alpha Centauri AB is unlikely to be entirely accidental, as it shares approximately the same motion through space as the inner binary star system. However, true gravitational binding is yet to be proven.

Seen from Earth, Proxima Centauri is 2.2 degrees south-west from Alpha Centauri AB. This is about four times the angular diameter of the Full Moon, and almost exactly half the distance between Alpha Centauri and Beta Centauri. A moderate-sized telescope is required to see Proxima.

Proxima usually appears as a 13.1 visual magnitude deep-red star in a poor star field of only several stars. The star is listed in the General Catalogue of Variable Stars (G.C.V.S. Version 4.2) as V645 Cen, being a known UV Ceti-type flare star, which may suddenly and unexpectedly brighten by about two magnitudes or so. (A visual magnitude of 11.0 is often quoted.) Both amateur and professional astronomers monitor this star from time to time - with both optical and radio telescopes. Proxima is of spectral class M5Ve or M5VIe, whose B-V colour index is +1.81. The spectral class suggest this is either a small main sequence star (Type V) or sub-dwarf (VI) with emission lines. Its mass is about 0.4 solar masses.

The closest stars to the Alpha Centauri system are the Sun and Barnard's star (1.98 pc or 6.47 ly). From Earth, Barnard's star is currently 5.96 ly. away.

Alpha Centauri: A High Proper Motion System

Alpha Centauri, like the first magnitude stars of Sirius and Arcturus, shows high proper motions against the background sky, which causes its sky position to gradually change over the centuries. These slow motions were unknown to ancient astronomers, like Aristotle, who stated that all stars were permanently fixed to their places on the celestial sphere. Edmond Halley in 1718 first found that contemporary astrometric sky positions, especially of the bright star Arcturus, differed significantly from those given by Ptolemy (probably measured earlier by Hipparchos) during the 1st Century B.C. (In Arcturus' case, the star moved almost ½ degree in 1800 years.) These motions were found mainly for northern stars, and thus the motion of the southern star Alpha Centauri was not found until the early 17th Century.

As stated above, Thomas Henderson in the 1830s was the first to discover Alpha Centauri's true distance, but also soon realised that this system was likely to have a high proper motion. Because of the proximity of these stars, their true velocity through space would appear to be much larger. In Alpha Centauri's case, the apparent motion of these stars were found from the astrometric observations made by Abbé Nicolas Louis de Lacaille during 1751-52.

Using the Hipparcos Star Catalogue (HIP) data, the mean individual proper motions (in milli arcsec) are -3678 mas.yr^-1 (mas/yr) or 3.678 arcsec per year in right ascension (the negative value indicating the sky motion is east to west) and +481.84 mas.yr^-1 (mas/yr) or 0.48184 arcsec per year in declination. As proper motions are cumulative, the motion of Alpha Centauri is about 6.1 arcmin/century (367.8 arcsec/ century) equivalent to 1.02 degrees/millennia or 61.3 arcmin/millennia. These motions are about one-fifth and twice, respectively, the diameter of the full moon.

A rough calculation, for example, shows that the current distance of 4.4 degrees between Alpha and Beta Centauri will take about 4200 years by proper motion to cross, therefore these two naked-eye stars will be closest in about A.D. 6200. Calculating backwards in time, say to the time of 2000 years ago, the pointers of Alpha and Beta Centauri were about 6½ degrees apart, and Alpha Centauri was instead lying in the present day southern constellation of Circinus.

A more precise calculation can be made that involves taking into account the slight changes in the distance of the star by its own motion, and in Alpha Centauri's case, this means a slow increase in the values of these proper motions. Slight variances are also due to the small difference in measured values of the proper motions of α Cen A and α Cen B, which is roughly about 0.5% in accuracy.

Future Sky Positions of Alpha Centauri

Around A.D. 5973 (or as sometimes expressed 5973 C.E), the significantly very high proper motions observed for the stars of Alpha Centauri will eventually lead to some future observer seeing a brilliant naked-eye visual double star adjoining the slightly fainter 1st magnitude star Beta Centauri / β Centauri. At closest approach, the apparent separation of these stars will be only 23 arcmin or two-thirds the Moon's apparent diameter.^{citation needed} ^[11] This spectacular duo will form a very rare optical stellar conjunction. Comparing to the large general motion of α Centauri, β Centauri is roughly one-hundredth its overall motion. (β Centauri's proper motions being -33.96 mas.yr^-1 in R.A. and -2.506 mas.yr^-1 in Dec., respectively.) As such, β Centauri appears almost stationary over the centuries or millennia in its general position against the background stars. This difference in proper motion is primarily caused by β Centauri lying just over 120 times farther away from us than Alpha Centauri itself. (530 light-years compared to 4.3 light-years). So it is really the overall large apparent motion α Centauri that has formed this future optical alignment, making the stars more akin to slowly passing one another as two ships in the night.

After this, Alpha Centauri will continue to slowly brighten, passing just north of the Southern Cross or Crux, before moving northwest and up towards the celestial equator and away from the galactic plane. By about 29,700 A.D., α Centauri will lie exactly 1.00 parsecs or 3.26 light-years away, reaching the maximum brightness of -0.86 visual magnitude - similar in brightness to present day Canopus. At this time it will be placed near the present-day constellation of Hydra. Soon after this relatively close solar approach, the system will then begin to move away from the Sun. In 43,300 A.D., α Centauri will pass near 2nd magnitude Alpha Hydrae / Alphard. Then the apparent visual magnitude will be +1.03 and lie 5.36 ly. away. ^[12]

As the star slowly disappears among the stars of the Milky Way, it will reach a final vanishing point location, due to visual perspective, more than 100,000 years from now. Here this once bright star will finally drop below naked-eye visibility somewhere in the faint southern constellation of Telescopium. This unusual location results from α Centauri's independent galactic motion being highly tilted with respect to the plane of our Milky Way galaxy.

The Sky from Alpha Centauri

Viewed from near the Alpha Centauri system, the sky would appear very much as it does to observers on Earth, except being without the three stars of α Centauri. Most of the familiar constellations, such as Ursa Major and Orion, would appear almost unchanged. However, Centaurus would be missing its brightest star, and our Sun would appear as star of +0.5 magnitude in the northern Milky Way constellation of Cassiopeia. An interstellar observer would find the familiar \/\/ shape of Cassiopeia becoming a /\/\/, with the Sun being at the end closest to the star ε Cassiopeiae. The Sun's position is easily plotted, as it lies at the point antipodal to Alpha Centauri's current position as seen from Earth. This is at RA 02h 39m 35s, Dec. +60° 50' (2000)

From Alpha Centauri, the bright stars which are relatively close to us, such as Sirius, Procyon and Altair, would appear to have quite different sky positions. Sirius, for example, would been seen to become part of the constellation of Orion, appearing some 2 degrees west of Betelgeuse. It would also be -1.2 magnitude star - some 0.2 magnitudes dimmer than seen from Earth. Other bright stars like Fomalhaut and Vega, although slightly further away, would appear only slightly displaced from their familiar positions in the sky.

Due to the low luminosity of Proxima Centauri, to the naked-eye it would remain an inconspicuous 4.5 magnitude star even though being merely 0.25 light-year away. Its slow and gradual movement against the stars of the background sky would probably be detectable to the average person over one or two decades.

From Proxima itself, α Centauri AB would appear like two close very bright stars with the combined magnitude of −6.80. Depending on the position of the binary in their orbit, the stars would appear noticeably double to the naked eye or occasionally, for a short time, as one unresolved star. In visual magnitude, α Cen A would be −6.52, and α Cen B −5.19.

Does Alpha Centauri Have Planets?

Discovery of additional planets orbiting both single stars and binary star systems, leaves the real possibility of finding either new planets in the Alpha Centauri AB system or planets revolving close to either α Cen A or α Cen B. With additional evidence, like both the principle stars being similar in nature to the Sun, I.e. high metallicity and similar ages, simply reinforces the astronomers view that it is very worthwhile to make detailed searches for planetary bodies around Alpha Centauri. Additionally, planets have also been found in other similar binary systems. I.e. Gamma Cephei. Several established planet-hunting teams have used various radial velocity or star transit methods in their searches around these two bright stars. All observational studies have so far failed to find any suggestion of either brown dwarfs, gas giants (planets) or small extrasolar terrestrial planets.

Based on theoretical computer simulations, other planetary astronomers consider that any potential terrestrial planets that did once orbit near the stars' habitable zones are now likely no longer located there. The loss several billion years ago of these small bodies probably happened during the system's formation. All may have since been ejected by significant disruptions caused by strong gravitational or perturbation effects generated between the two main stellar components.

In the not too distant future, assuming our human technology advances enough to enable voyages for interstellar robotic probes, Alpha Centauri may be first on the list for exo-planetary exploration. Such lengthy trips to cross the huge empty gulfs between the stars would likely still take several centuries, and this still assumes that some interstellar spacecraft could obtain high enough velocities to get there. If present ground or orbit based observatories are unable to detect planets, future unmanned exploratory journeys will be the only means of obtaining direct evidence that such planets do exist.

Alpha Centauri From a Hypothetical Planet

Any hypothetical planet orbiting around either α Centauri A or α Centauri B would see the other star as an intensely bright star in the sky with a discernible disk. For example, an Earth-like planet about 1.25 Astronomical Unit (A.U.) from α Cen A (with an orbital period of about one year three months or 1.3(4) a) would get Sun-like illumination from its primary, where α Cen B would appear 5.7 to 8.6 magnitudes dimmer (−21.0 to −18.2), 190 to 2700 times dimmer than α Cen A but still 170 to 2300 times brighter than the full moon. Conversely, a similar Earth-like planet at 0.71 A.U. from α Cen B (with the revolution period of about 0.6(3) a) would get Sun-like illumination from its primary, where α Cen A would appear 4.6 to 7.3 magnitudes dimmer (−22.1 to −19.4), 70 to 840 times dimmer than α Cen B but still 520 to 6300 times brighter than the full moon. In both these cases, in the course of the planet's year, the secondary sun would appear to circle the whole sky. Either way, any such hypothetical Earth-like planet would find that the secondary sun would not be bright enough to significantly influence climate or plant photosynthesis.

If one assumes the planet has a low orbital inclination with respect to the mutual orbit of α Cen A and B, then the secondary star would start beside the primary at conjunction. Half a period (about forty years) later, at opposition, both stars would be opposite each other in the sky. At this time, for about half the planetary year the appearance of the night sky would be dark blue - similar to our sky during a total solar eclipse. People could easily walk around and clearly see the surrounding terrain. Even reading a book would be quite possible without any artificial light. After another half period in the stellar orbit, the stars would complete the cycle and return to conjunction. At this time an Earth-like day and night cycle would return.

Possibilities In Planet Formation

Some recent computer models regarding planetary formation, do predict the possibility of terrestrial planets existing around both Alpha Centauri A and B ^[13]^[14]^[15]. Some other models also strongly suggested that formation of gas giant planets similar to our Jupiter and Saturn remain unlikely because of the significant gravitational and angular momentum effects of this binary system.^[16] Given the similarities to the Sun in star type, age and probable stability of the orbits, it has been sometimes suggested that this stellar system could hold one of the best possibilities for extraterrestrial life.^[17] Although highly speculative, both these stars are of the right spectral type to possibly harbour life on some potential planet. ^[18]^[19]^[20]

However, some astronomers have speculated that any possible terrestrial planets in the Alpha Centauri system may be bone dry or lack significant atmospheres. This is because theoretically, both Jupiter and Saturn were very crucial in perturbing comets into the inner solar system, thus providing the inner planets with their own source of water and various other ices. This significant issue might not be as problematic, if for example, α Centauri B happened to have played a similar role as any hypothetical giant gas planets orbiting α Centauri A. (or conversely, α Cen A for α Cen B.) Also against this view is that most comets are considered to reside in the outer regions of the stellar system in some huge Oort Cloud, and these comets can only sent sun-wards by the perturbations of gas planets or disruptions by the passing of nearby stars. As yet there is no direct evidence that such regions do exist around α Centauri AB, and it is indeed possible that this theoretical Oort Cloud region was totally destroyed during the system's own formation.

Any suspected Earth-like planet around Alpha Centauri A would have to be placed about 1.25 AU away - about halfway between the distances of Earth's orbit and Mars' orbit in our own Solar System, so as to have similar planetary temperatures and conditions for liquid water to exist. For the slightly less luminous and cooler Alpha Centauri B, this distance would be closer to its star at about 0.7 AU, being about the distance that Venus is from the Sun.

To find evidence of such planets, currently both Proxima Centauri and α Centauri AB are among the listed "Tier 1" target stars for NASA's Space Interferometry Mission (SIM). SIM is designed to be able to detect planets as small as three Earth-masses or smaller within two Astronomical Units of a "Tier 1" target.^[21]

Origin of Name and Cultural Significance

The system bears the proper name Rigil Kentaurus^[22] (often shortened to Rigil Kent.^[23], former Rigjl Kentaurus^[24]^[25], and Riguel Kentaurus^[26] in Portuguese), derived from the Arabic phrase Rijl Qantūris^[23] (or Rijl al-Qantūris,^[27] meaning "Foot of the Centaur)," but is most often referred to by its Bayer designation Alpha Centauri. An alternative name is Toliman, whose etymology may be Arabic al-Zulmān (meaning "the Ostriches")^[23], or Hebrew (meaning "The Heretofore and the Hereafter" and/or "Shoot of the Vine").^{citation needed} (See Centaurus) Finally, it is sometimes called Bungula^[28], possibly coined from "β" and the Latin ungula (meaning "hoof").^[23] This latter name in modern times is, however, rarely used.

In Chinese, Alpha Centauri was called Nánmén'èr (南門二) "Second Star of the Southern Gate". As mentioned, Alpha and Beta Centauri together form the "Southern Pointers" to Crux, the Southern Cross.

Alpha Centauri in Modern Fiction

References

^ LHS 50 -- High proper-motion Star. Centre de Données astronomiques de Strasbourg. Retrieved on 2008-06-06.
^ LHS 51 -- High proper-motion Star. Centre de Données astronomiques de Strasbourg. Retrieved on 2008-06-06.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ Kervella, Pierre; Thevenin, Frederic (March 15, 2003). A Family Portrait of the Alpha Centauri System. ESO. Retrieved on 2008-06-06.
^ Gilli, G.; Israelian, G.; Ecuvillon, A.; Santos, N. C.; Mayor, M. (2006). "Abundances of Refractory Elements in the Atmospheres of Stars with Extrasolar Planets". Astronomy and Astrophysics 449 (2): 723–736. doi:10.1051/0004-6361:20053850. Retrieved on 2007-06-01.
^ Kervella, Pierre; Thévenin, Frédéric; Du Foresto, Vincent Coudé; Mignard, François (2007). "Deep imaging survey of the environment of Alpha Centauri - I. Adaptive optics imaging of Alpha Cen B with VLT-NACO". Astronomy and astrophysics 464 (1): 367–372. Retrieved on 2008-06-06.
^ Pourbaix, D.; Nidever, D.; McCarthy, C.; Butler, R. P.; Tinney, C. G.; Marcy, G. W.; Jones, H. R. A.; Penny, A. J.; Carter, B. D.; Bouchy, F.;+ 6 more (2002). "Constraining the difference in convective blueshift between the components of alpha Centauri with precise radial velocities". Astronomy and Astrophysics 386 (1): 208–285. doi:10.1051/0004-6361:20020287. Retrieved on 2008-06-15.
^ Heintz, W.D. (1978). Double Stars. D. Reidel Publishing Company, Dordrecht, 19.
^ Guinan, E.; Messina, S.. "IAU Circular 6259, Alpha Centauri B", Central Bureau for Astronomical Telegrams.
^ Robrade, J.; Schmitt, J.H.M.M., Favata, F. (2005). "X-rays from α Centauri - The darkening of the solar twin". Astronomy and Astrophysics 442 (1): 315–321. Retrieved on 2008-06-27.
^ ^a ^b Hartkopf, W.; Mason, D. M.. "Sixth Catalog of Orbits of Visual Binaries", U.S.Naval Observatory, Washingto D.C..
^ Hartung, E.J.; Frew, David Malin, David. "Astronomical Objects for Southern Telescopes", Cambridge University Press.
^ Matthews, R.A.J. (1994). "The Close Approach of Stars in the Solar Neighbourhood". Quarterly Journal of the Royal Astronomical Society 35: 1 – 8.
^ Javiera Guedes, Terrestrial Planet Formation Around Alpha Cen B
^ see Lissauer and Quintana in references below
^ Javiera M. Guedes, Eugenio J. Rivera, Erica Davis, Gregory Laughlin, Elisa V. Quintana, Debra A. Fischer (to be published in 2008). Formation and Detectability of Terrestrial Planets Around Alpha Centauri B. Astrophysical Journal.
^ M. Barbier, F. Marzari, H. Scholl (2002). "Formation of terrestrial planets in close binary systems: The case of α Centauri A". Astronomy & Astrophysics 396: 219 – 224. doi:10.1051/0004-6361:20021357.
^ P.A. Wiegert and M.J. Holman (1997). "The stability of planets in the Alpha Centauri system". The Astronomical Journal 113: 1445 – 1450.
^ Lissauer, J. J., E. V. Quintana, J. E. Chambers, M. J. Duncan, and F. C. Adams. (2004). "Terrestrial Planet Formation in Binary Star Systems.". "Revista Mexicana de Astronomia y Astrofisica (Serie de Conferencias); First Astrophysics meeting of the Observatorio Astronomico Nacional: Gravitational Collapse: From Massive Stars to Planets"; 22: 99 – 103.
^ Quintana, E. V.; Lissauer, J. J.; Chambers, J. E.; Duncan, M. J.; (2002). "Terrestrial Planet Formation in the Alpha Centauri System.". Astrophysical Journal 2: 982–996. doi:10.1086/341808.
^ Quintana, E. V.; Lissauer, J. J.;. "Terrestrial Planet Formation in Binary Star Systems.". "Planets in Binary Star Systems.".
^ "Planet Hunting by Numbers," (Press Release), NASA, Stars and Galaxies, Jet Propulsion Laboratory, 18 October 2006. Retrieved 24 April 2007.
^ Bailey, F., "The Catalogues of Ptolemy, Ulugh Beigh, Tycho Brahe, Halley, and Hevelius," Memoirs of Royal Astronomical Society, vol. XIII, London, 1843.
^ ^a ^b ^c ^d Kunitzsch P., & Smart, T., A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations, Cambride, Sky Pub. Corp., 2006, p. 27
^ Hyde T., "Ulugh Beighi Tabulae Stellarum Fixarum", Tabulae Long. ac Lat. Stellarum Fixarum ex Observatione Ulugh Beighi, Oxford, 1665, p. 142.
^ Hyde T., "In Ulugh Beighi Tabulae Stellarum Fixarum Commentarii", op. cit., p. 67.
^ da Silva Oliveira, R., "Crux Australis: o Cruzeiro do Sul", Artigos: Planetario Movel Inflavel AsterDomus.
^ Davis Jr., G. A., "The Pronunciations, Derivations, and Meanings of a Selected List of Star Names,"Popular Astronomy, Vol. LII, No. 3, Oct. 1944, p. 16.
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