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91-525: (Redirected from Tolimán ) Toliman or Tolimán may refer to: The star Alpha Centauri B. Tolimán (Jalisco) , a town in the Mexican state of Jalisco. Tolimán (Querétaro) , a town in the Mexican state of Querétaro. Volcán Tolimán , a stratovolcano in Guatemala. See also [ edit ] Tolima (disambiguation) Tolman Topics referred to by

182-402: A binary component. The AB designation, or older A×B , denotes the mass centre of a main binary system relative to companion star(s) in a multiple star system. AB-C refers to the component of Proxima Centauri in relation to the central binary, being the distance between the centre of mass and the outlying companion. Because the distance between Proxima (C) and either of Alpha Centauri A or B

273-482: A " super-Earth " class planet orbiting in the habitable zone where liquid water can exist on the surface. Computer simulations of the formation of planets around low-mass stars predict that Earth-sized planets are most abundant, but more than 90% of the simulated planets are at least 10% water by mass, suggesting that many Earth-sized planets orbiting red dwarf stars are covered in deep oceans. At least four and possibly up to six exoplanets were discovered orbiting within

364-548: A brilliant optical double star in the southern sky. It will then pass just north of the Southern Cross or Crux , before moving northwest and up towards the present celestial equator and away from the galactic plane . By about 26,700  CE , in the present-day constellation of Hydra , α Centauri will reach perihelion at 0.90  pc or 2.9  ly away, though later calculations suggest that this will occur in 27,000 AD. At its nearest approach, α Centauri will attain

455-573: A few minutes. Some amateur and professional astronomers regularly monitor for outbursts using either optical or radio telescopes. In August 2015, the largest recorded flares of the star occurred, with the star becoming 8.3 times brighter than normal on 13 August, in the B ;band (blue light region) . Alpha Centauri may be inside the G-cloud of the Local Bubble , and its nearest known system

546-492: A fraction of a degree since Ptolemy 's time due to proper motion .) In Ptolemy's time, Alpha Centauri was visible from Alexandria, Egypt , at 31° N, but, due to precession , its declination is now –60° 51′ South , and it can no longer be seen at that latitude. English explorer Robert Hues brought Alpha Centauri to the attention of European observers in his 1592 work Tractatus de Globis , along with Canopus and Achernar , noting: Now, therefore, there are but three Stars of

637-399: A high proper motion. In this case, the apparent stellar motion was found using Nicolas Louis de Lacaille 's astrometric observations of 1751–1752, by the observed differences between the two measured positions in different epochs. Calculated proper motion of the centre of mass for α Centauri AB is about 3620 mas/y (milliarcseconds per year) toward the west and 694 mas/y toward

728-459: A low fusion rate, and hence, a low temperature. The energy generated is the product of nuclear fusion of hydrogen into helium by way of the proton–proton (PP) chain mechanism. Hence, these stars emit relatively little light, sometimes as little as 1 ⁄ 10,000 that of the Sun, although this would still imply a power output on the order of 10  watts (10 trillion gigawatts or 10 ZW ). Even

819-862: A mass between that of Neptune and one-half that of Saturn, though it may be a dust disk or an artifact. The possibility of C1 being a background star has been ruled out. If this candidate is confirmed, the temporary name C1 will most likely be replaced with the scientific designation Alpha Centauri Ab in accordance with current naming conventions. GO Cycle 1 observations are planned for the James Webb Space Telescope (JWST) to search for planets around Alpha Centauri A, as well as observations of Epsilon Muscae . The coronographic observations, which occurred on July 26 and 27, 2023, were failures, though there are follow-up observations in March 2024. Pre-launch estimates predicted that JWST will be able to find planets with

910-459: A mass of roughly 7 M E and orbits about 1.49 AU from Proxima Centauri with a period of 1,928 days (5.28 yr). In June 2020, a possible direct imaging detection of the planet hinted at the presence of a large ring system. However, a 2022 study disputed the existence of this planet. A 2020 paper refining Proxima b's mass excludes the presence of extra companions with masses above 0.6  M E at periods shorter than 50 days, but

1001-464: A maximum apparent magnitude of −0.86, comparable to present-day magnitude of Canopus , but it will still not surpass that of Sirius , which will brighten incrementally over the next 60,000 years, and will continue to be the brightest star as seen from Earth (other than the Sun) for the next 210,000 years. Alpha Centauri is a triple star system, with its two main stars, A and B, together comprising

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1092-587: A passing comet from his station in Puducherry . Alpha Centauri was only the third binary star to be discovered, preceded by Mizar AB and Acrux . The large proper motion of Alpha Centauri AB was discovered by Manuel John Johnson , observing from Saint Helena , who informed Thomas Henderson at the Royal Observatory, Cape of Good Hope of it. The parallax of Alpha Centauri was subsequently determined by Henderson from many exacting positional observations of

1183-424: A radius of 5 R 🜨 at 1–3 AU . Multiple observations every 3–6 months could push the limit down to 3 R 🜨 . Post-launch estimates based on observations of HIP 65426 b find that JWST will be able to find planets even closer to Alpha Centauri A and could find a 5 R 🜨 planet at 0.5–2.5 AU . Candidate 1 has an estimated radius between 3.3–11 R 🜨 and orbits at 1.1 AU . It

1274-485: A red dwarf. First, planets in the habitable zone of a red dwarf would be so close to the parent star that they would likely be tidally locked . For a nearly circular orbit, this would mean that one side would be in perpetual daylight and the other in eternal night. This could create enormous temperature variations from one side of the planet to the other. Such conditions would appear to make it difficult for forms of life similar to those on Earth to evolve. And it appears there

1365-410: A star does not have a strict definition. One of the earliest uses of the term was in 1915, used simply to contrast "red" dwarf stars from hotter "blue" dwarf stars. It became established use, although the definition remained vague. In terms of which spectral types qualify as red dwarfs, different researchers picked different limits, for example K8–M5 or "later than K5". Dwarf M star , abbreviated dM,

1456-474: A terrestrial planet discovered in 2016 by astronomers at the European Southern Observatory (ESO). It has an estimated minimum mass of 1.17 M E ( Earth masses ) and orbits approximately 0.049 AU from Proxima Centauri, placing it in the star's habitable zone . The discovery of Proxima Centauri c was formally published in 2020 and could be a super-Earth or mini-Neptune . It has

1547-489: A wide variety of stars indicate about 1 in 6 stars with twice the mass of the Sun are orbited by one or more of Jupiter-sized planets, versus 1 in 16 for Sun-like stars and the frequency of close-in giant planets (Jupiter size or larger) orbiting red dwarfs is only 1 in 40. On the other hand, microlensing surveys indicate that long-orbital-period Neptune -mass planets are found around one in three red dwarfs. Observations with HARPS further indicate 40% of red dwarfs have

1638-518: Is Bram-bram-bult . To the naked eye, α Centauri AB appears to be a single star, the brightest in the southern constellation of Centaurus . Their apparent angular separation varies over about 80 years between 2 and 22 arcseconds (the naked eye has a resolution of 60 arcsec), but through much of the orbit, both are easily resolved in binoculars or small telescopes. At −0.27 apparent magnitude (combined for A and B magnitudes (see Apparent magnitude § Magnitude addition ) ), Alpha Centauri

1729-652: Is circumpolar and never sets below the horizon. North of about 29° N latitude, Alpha Centauri never rises. Alpha Centauri lies close to the southern horizon when viewed from the 29° North latitude to the equator (close to Hermosillo and Chihuahua City in Mexico ; Galveston, Texas ; Ocala, Florida ; and Lanzarote , the Canary Islands of Spain ), but only for a short time around its culmination . The star culminates each year at local midnight on 24 April and at local 9 p.m. on 8 June. As seen from Earth, Proxima Centauri

1820-626: Is 2.2° southwest from α Centauri AB ; this distance is about four times the angular diameter of the Moon . Proxima Centauri appears as a deep-red star of a typical apparent magnitude of 11.1 in a sparsely populated star field, requiring moderately sized telescopes to be seen. Listed as V645 Cen in the General Catalogue of Variable Stars , version 4.2, this UV Ceti star or "flare star" can unexpectedly brighten rapidly by as much as 0.6 magnitude at visual wavelengths, then fade after only

1911-639: Is 35.6 AU (5.33 × 10 ^  km), about the distance between the Sun and Pluto. The most recent periastron was in August 1955 and the next will occur in May ;2035; the most recent apastron was in May 1995 and will next occur in 2075. Viewed from Earth, the apparent orbit of A and B means that their separation and position angle (PA) are in continuous change throughout their projected orbit. Observed stellar positions in 2019 are separated by 4.92 arcsec through

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2002-449: Is Golius' latinisation of the Arabic name الظلمان al-Ẓulmān "the ostriches", the name of an asterism of which Alpha Centauri formed the main star. α Centauri C was discovered in 1915 by Robert T. A. Innes , who suggested that it be named Proxima Centaurus , from Latin  'the nearest [star] of Centaurus '. The name Proxima Centauri later became more widely used and

2093-496: Is a first-magnitude star and is fainter only than Sirius and Canopus . It is the outer star of The Pointers or The Southern Pointers , so called because the line through Beta Centauri (Hadar/Agena), some 4.5° west, points to the constellation Crux —the Southern Cross. The Pointers easily distinguish the true Southern Cross from the fainter asterism known as the False Cross . South of about 29° South latitude, α Cen

2184-427: Is a great problem with the atmosphere of such tidally locked planets: the perpetual night zone would be cold enough to freeze the main gases of their atmospheres, leaving the daylight zone bare and dry. On the other hand, though, a theory proposes that either a thick atmosphere or planetary ocean could potentially circulate heat around such a planet. Variability in stellar energy output may also have negative impacts on

2275-418: Is also potentially habitable, was discovered. Gliese 581c and d are within the habitable zone of the host star, and are two of the most likely candidates for habitability of any exoplanets discovered so far. Gliese 581g , detected September 2010, has a near-circular orbit in the middle of the star's habitable zone. However, the planet's existence is contested. On 23 February 2017 NASA announced

2366-479: Is an approximation of the Arabic الظليمان aẓ-Ẓalīmān (in older transcription, aṭ-Ṭhalīmān ), meaning 'the (two male) Ostriches', an appellation Zakariya al-Qazwini had applied to the pair of stars Lambda and Mu Sagittarii ; it was often not clear on old star maps which name was intended to go with which star (or stars), and the referents changed over time. The name Toliman originates with Jacobus Golius ' 1669 edition of Al-Farghani 's Compendium . Tolimân

2457-517: Is approximately 511 000 +41 000 −30 000 years, with an eccentricity of 0.5, much more eccentric than Mercury 's. Proxima Centauri comes within 4100 +700 −600   AU of AB at periastron, and its apastron occurs at 12 300 +200 −100   AU . Asteroseismic studies, chromospheric activity , and stellar rotation ( gyrochronology ) are all consistent with the Alpha Centauri system being similar in age to, or slightly older than,

2548-414: Is comparable to that of the Sun, showing coronal variability due to star spots , as modulated by the rotation of the star. However, since 2005 the activity level has fallen into a deep minimum that might be similar to the Sun's historical Maunder Minimum . Alternatively, it may have a very long stellar activity cycle and is slowly recovering from a minimum phase. Alpha Centauri B, also known as Toliman,

2639-404: Is decreased, and instead convection is the main form of energy transport to the surface of the star. Above this mass, a red dwarf will have a region around its core where convection does not occur. Because low-mass red dwarfs are fully convective, helium does not accumulate at the core, and compared to larger stars such as the Sun, they can burn a larger proportion of their hydrogen before leaving

2730-416: Is different from Wikidata All article disambiguation pages All disambiguation pages Alpha Centauri Alpha Centauri ( α Centauri , α Cen , or Alpha Cen ) is a triple star system in the southern constellation of Centaurus . It consists of three stars: Rigil Kentaurus ( α Centauri A ), Toliman ( α Centauri B ), and Proxima Centauri ( α Centauri C ). Proxima Centauri

2821-481: Is more magnetically active than Alpha Centauri A, showing a cycle of 8.2 ± 0.2 yr compared to 11 years for the Sun, and has about half the minimum-to-peak variation in coronal luminosity of the Sun. Alpha Centauri B has an apparent magnitude of +1.35, slightly dimmer than Mimosa . Alpha Centauri C, better known as Proxima Centauri, is a small main-sequence red dwarf of spectral class M6-Ve. It has an absolute magnitude of +15.60, over 20,000 times fainter than

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2912-619: Is now listed by the International Astronomical Union (IAU) as the approved proper name; commonly, it is frequently abbreviated to Proxima . In 2016, the Working Group on Star Names of the IAU, having decided to attribute proper names to individual component stars rather than to multiple systems , approved the name Rigil Kentaurus ( / ˈ r aɪ dʒ əl k ɛ n ˈ t ɔːr ə s / ) as being restricted to α Centauri A and

3003-415: Is part of the α Centauri system and slightly closer to Earth than α Centauri AB . As such, Innes concluded that Proxima Centauri was the closest star to Earth yet discovered. All components of α Centauri display significant proper motion against the background sky. Over centuries, this causes their apparent positions to slowly change. Proper motion was unknown to ancient astronomers. Most assumed that

3094-480: Is similar, the AB binary system is sometimes treated as a single gravitational object. The A and B components of Alpha Centauri have an orbital period of 79.762 years. Their orbit is moderately eccentric , as it has an eccentricity of almost 0.52; their closest approach or periastron is 11.2 AU (1.68 × 10 ^  km), or about the distance between the Sun and Saturn; and their furthest separation or apastron

3185-465: Is the closest star to the Sun at 4.2465  light-years (1.3020  pc ). α Centauri A and B are Sun-like stars ( class G and K , respectively) that together form the binary star system α Centauri AB . To the naked eye , these two main components appear to be a single star with an apparent magnitude of −0.27 . It is the brightest star in the constellation and the third-brightest in

3276-419: Is the binary brown dwarf system Luhman 16 , at 3.6 light-years (1.1 parsecs ) from Alpha Centauri. Alpha Centauri is listed in the 2nd century the star catalog appended to Ptolemy 's Almagest . He gave its ecliptic coordinates , but texts differ as to whether the ecliptic latitude reads 44° 10′ South or 41° 10′ South . (Presently the ecliptic latitude is 43.5° South , but it has decreased by

3367-532: Is the principal member, or primary, of the binary system. It is a solar-like main-sequence star with a similar yellowish colour, whose stellar classification is spectral type G2-V; it is about 10% more massive than the Sun, with a radius about 22% larger. When considered among the individual brightest stars in the night sky, it is the fourth-brightest at an apparent magnitude of +0.01, being slightly fainter than Arcturus at an apparent magnitude of −0.05. The type of magnetic activity on Alpha Centauri A

3458-467: Is the secondary star of the binary system. It is a main-sequence star of spectral type K1-V, making it more an orange colour than Alpha Centauri A; it has around 90% of the mass of the Sun and a 14% smaller diameter. Although it has a lower luminosity than A, Alpha Centauri B emits more energy in the X-ray band. Its light curve varies on a short time scale, and there has been at least one observed flare . It

3549-412: Is therefore likely within the reach of JWST observations. The first claim of a planet around Alpha Centauri B was that of Alpha Centauri Bb in 2012, which was proposed to be an Earth-mass planet in a 3.2-day orbit. This was refuted in 2015 when the apparent planet was shown to be an artifact of the way the radial velocity data was processed. A search for transits of planet Bb was conducted with

3640-688: The Centaur . The common name Rigil Kentaurus is a Latinisation of the Arabic translation رجل القنطورس Rijl al-Qinṭūrus, meaning "the Foot of the Centaur ". Qinṭūrus is the Arabic transliteration of the Greek Κένταυρος (Kentaurus). The name is frequently abbreviated to Rigil Kent ( / ˈ r aɪ dʒ əl ˈ k ɛ n t / ) or even Rigil , though the latter name is better known for Rigel ( β Orionis). An alternative name found in European sources, Toliman ,

3731-466: The Gliese ;581 planetary system between 2005 and 2010. One planet has about the mass of Neptune , or 16  Earth masses ( M E ). It orbits just 6 million kilometres (0.040  AU ) from its star, and is estimated to have a surface temperature of 150  °C (423  K ; 302  °F ), despite the dimness of its star. In 2006, an even smaller exoplanet (only 5.5  M E )

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3822-703: The Hubble Space Telescope from 2013 to 2014. This search detected one potential transit-like event, which could be associated with a different planet with a radius around 0.92  R 🜨 . This planet would most likely orbit Alpha Centauri B with an orbital period of 20.4 days or less, with only a 5% chance of it having a longer orbit. The median of the likely orbits is 12.4 days. Its orbit would likely have an eccentricity of 0.24 or less. It could have lakes of molten lava and would be far too close to Alpha Centauri B to harbour life . If confirmed, this planet might be called Alpha Centauri Bc . However,

3913-408: The main sequence . As a result, red dwarfs have estimated lifespans far longer than the present age of the universe, and stars less than 0.8  M ☉ have not had time to leave the main sequence. The lower the mass of a red dwarf, the longer the lifespan. It is believed that the lifespan of these stars exceeds the expected 10-billion-year lifespan of the Sun by the third or fourth power of

4004-422: The night sky , outshone by only Sirius and Canopus . α Centauri A (Rigil Kentaurus) has 1.1 times the mass and 1.5 times the luminosity of the Sun , while α Centauri B (Toliman) is smaller and cooler, at 0.9 solar mass and less than 0.5 solar luminosity. The pair orbit around a common centre with an orbital period of 79 years. Their elliptical orbit is eccentric , so that

4095-401: The AB system between April 1832 and May 1833. He withheld his results, however, because he suspected they were too large to be true, but eventually published them in 1839 after Bessel released his own accurately determined parallax for 61 Cygni in 1838. For this reason, Alpha Centauri is sometimes considered as the second star to have its distance measured because Henderson's work

4186-463: The Alpha Centauri system. Several established planet-hunting teams have used various radial velocity or star transit methods in their searches around these two bright stars. All the observational studies have so far failed to find evidence for brown dwarfs or gas giants . In 2009, computer simulations showed that a planet might have been able to form near the inner edge of Alpha Centauri B's habitable zone, which extends from 0.5–0.9 AU from

4277-1053: The Greek letter beta ( β ) and Latin ungula 'hoof', originally for Beta Centauri (the other hoof). In Chinese astronomy , 南門 Nán Mén , meaning Southern Gate , refers to an asterism consisting of Alpha Centauri and Epsilon Centauri . Consequently, the Chinese name for Alpha Centauri itself is 南門二 Nán Mén Èr , the Second Star of the Southern Gate. To the Indigenous Boorong people of northwestern Victoria in Australia, Alpha Centauri and Beta Centauri are Bermbermgle , two brothers noted for their courage and destructiveness, who speared and killed Tchingal "The Emu" (the Coalsack Nebula ). The form in Wotjobaluk

4368-425: The K dwarf classification. Other definitions are also in use. Many of the coolest, lowest mass M dwarfs are expected to be brown dwarfs, not true stars, and so those would be excluded from any definition of red dwarf. Stellar models indicate that red dwarfs less than 0.35  M ☉ are fully convective . Hence, the helium produced by the thermonuclear fusion of hydrogen is constantly remixed throughout

4459-645: The PA of 337.1°, increasing to 5.49 arcsec through 345.3° in 2020. The closest recent approach was in February 2016, at 4.0 arcsec through the PA of 300°. The observed maximum separation of these stars is about 22 arcsec, while the minimum distance is 1.7 arcsec. The widest separation occurred during February 1976, and the next will be in January 2056. Alpha Centauri C is about 13,000 AU (0.21 ly; 1.9 × 10 ^  km) from Alpha Centauri AB, equivalent to about 5% of

4550-652: The Solar System. This gives a speed with respect to the Sun of 32.4 km/s (20.1 mi/s), very close to the peak in the distribution of speeds of nearby stars. Since α Centauri AB is almost exactly in the plane of the Milky Way as viewed from Earth, many stars appear behind it. In early May 2028, α Centauri A will pass between the Earth and a distant red star, when there is a 45% probability that an Einstein ring will be observed. Other conjunctions will also occur in

4641-663: The Sun at 5 to 6 billion years, as derived by their mass and spectral characteristics. From the orbital elements , the total mass of Alpha Centauri AB is about 2.0  M ☉ – or twice that of the Sun. The average individual stellar masses are about 1.08  M ☉ and 0.91  M ☉ , respectively, though slightly different masses have also been quoted in recent years, such as 1.14  M ☉ and 0.92  M ☉ , totaling 2.06  M ☉ . Alpha Centauri A and B have absolute magnitudes of +4.38 and +5.71, respectively. Alpha Centauri A, also known as Rigil Kentaurus,

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4732-484: The Sun. Asteroseismic analyses that incorporate tight observational constraints on the stellar parameters for the Alpha Centauri stars have yielded age estimates of 4.85 ± 0.5 Gyr, 5.0 ± 0.5 Gyr, 5.2 ± 1.9 Gyr, 6.4 Gyr, and 6.52 ± 0.3 Gyr. Age estimates for the stars based on chromospheric activity (Calcium H & K emission) yield 4.4 ± 2.1 Gyr, whereas gyrochronology yields 5.0 ± 0.3 Gyr. Stellar evolution theory implies both stars are slightly older than

4823-400: The Sun. Its mass is calculated to be 0.1221   M ☉ . It is the closest star to the Sun but is too faint to be visible to the naked eye. The Alpha Centauri system as a whole has two confirmed planets, both of them around Proxima Centauri. While other planets have been claimed to exist around all of the stars, none of the discoveries have been confirmed. Proxima Centauri b is

4914-400: The authors detected a radial-velocity curve with a periodicity of 5.15 days, suggesting the presence of a planet with a mass of about 0.29  M E . This planet, Proxima Centauri d, was confirmed in 2022. In 2021, a candidate planet named Candidate 1 (or C1) was detected around Alpha Centauri A, thought to orbit at approximately 1.1 AU with a period of about one year, and to have

5005-445: The coming decades, allowing accurate measurement of proper motions and possibly giving information on planets. Based on the system's common proper motion and radial velocities, α Centauri will continue to change its position in the sky significantly and will gradually brighten. For example, in about 6,200  CE , α Centauri's true motion will cause an extremely rare first-magnitude stellar conjunction with Beta Centauri , forming

5096-428: The coolest true main-sequence stars into spectral types L2 or L3. At the same time, many objects cooler than about M6 or M7 are brown dwarfs, insufficiently massive to sustain hydrogen-1 fusion. This gives a significant overlap in spectral types for red and brown dwarfs. Objects in that spectral range can be difficult to categorize. Red dwarfs are very-low-mass stars . As a result, they have relatively low pressures,

5187-473: The development of life. Red dwarfs are often flare stars , which can emit gigantic flares, doubling their brightness in minutes. This variability makes it difficult for life to develop and persist near a red dwarf. While it may be possible for a planet orbiting close to a red dwarf to keep its atmosphere even if the star flares, more-recent research suggests that these stars may be the source of constant high-energy flares and very large magnetic fields, diminishing

5278-607: The discovery of seven Earth-sized planets orbiting the red dwarf star TRAPPIST-1 approximately 39 light-years away in the constellation Aquarius. The planets were discovered through the transit method, meaning we have mass and radius information for all of them. TRAPPIST-1e , f , and g appear to be within the habitable zone and may have liquid water on the surface. Modern evidence suggests that planets in red dwarf systems are extremely unlikely to be habitable. In spite of their great numbers and long lifespans, there are several factors which may make life difficult on planets around

5369-483: The distance between A and B varies from 35.6  astronomical units ( AU ), or about the distance between Pluto and the Sun, to 11.2 AU , or about the distance between Saturn and the Sun. α Centauri C , or more commonly, Proxima Centauri , is a small faint red dwarf ( class M ). Though not visible to the naked eye, Proxima Centauri is the closest star to the Sun at a distance of 4.24 ly (1.30 pc), slightly closer than α Centauri AB . Currently,

5460-418: The distance between Alpha Centauri AB and the Sun. Until 2017, measurements of its small speed and its trajectory were of too little accuracy and duration in years to determine whether it is bound to Alpha Centauri AB or unrelated. Radial velocity measurements made in 2017 were precise enough to show that Proxima Centauri and Alpha Centauri AB are gravitationally bound. The orbital period of Proxima Centauri

5551-416: The distance between Proxima Centauri and α Centauri AB is about 13,000  AU (0.21 ly), equivalent to about 430 times the radius of Neptune's orbit. Proxima Centauri has two confirmed planets: Proxima b or α Centauri Cb , an Earth-sized planet in the habitable zone discovered in 2016, and Proxima d ( α Centauri Cd ) , a candidate sub-Earth which orbits very closely to

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5642-489: The first generation of stars should have only hydrogen, helium, and trace amounts of lithium, and hence would be of low metallicity. With their extreme lifespans, any red dwarfs that were a part of that first generation ( population III stars ) should still exist today. Low-metallicity red dwarfs, however, are rare. The accepted model for the chemical evolution of the universe anticipates such a scarcity of metal-poor dwarf stars because only giant stars are thought to have formed in

5733-577: The first magnitude that I could perceive in all those parts which are never seene here in England . The first of these is that bright Star in the sterne of Argo which they call Canobus [Canopus]. The second [Achernar] is in the end of Eridanus . The third [Alpha Centauri] is in the right foote of the Centaure . The binary nature of Alpha Centauri AB was recognized in December 1689 by Jean Richaud, while observing

5824-434: The hotter and more massive end. One definition is synonymous with stellar M dwarfs ( M-type main sequence stars ), yielding a maximum temperature of 3,900 K and 0.6  M ☉ . One includes all stellar M-type main-sequence and all K-type main-sequence stars ( K dwarf ), yielding a maximum temperature of 5,200 K and 0.8  M ☉ . Some definitions include any stellar M dwarf and part of

5915-425: The lack of any brown dwarfs or gas giants in close orbits around Alpha Centauri make the likelihood of terrestrial planets greater than otherwise. A theoretical study indicates that a radial velocity analysis might detect a hypothetical planet of 1.8  M E in Alpha Centauri B's habitable zone . Red dwarf The coolest red dwarfs near the Sun have a surface temperature of about 2,000  K and

6006-406: The largest red dwarfs (for example HD 179930 , HIP 12961 and Lacaille 8760 ) have only about 10% of the Sun's luminosity . In general, red dwarfs less than 0.35  M ☉ transport energy from the core to the surface by convection . Convection occurs because of opacity of the interior, which has a high density compared to the temperature. As a result, energy transfer by radiation

6097-591: The least massive red dwarfs theoretically have temperatures around 1,700  K , while measurements of red dwarfs in the solar neighbourhood suggest the coolest stars have temperatures of about 2,075 K and spectral classes of about L2. Theory predicts that the coolest red dwarfs at zero metallicity would have temperatures of about 3,600 K . The least massive red dwarfs have radii of about 0.09  R ☉ , while both more massive red dwarfs and less massive brown dwarfs are larger. The spectral standards for M type stars have changed slightly over

6188-437: The main sequence for 2.5 trillion years, followed by five billion years as a blue dwarf, during which the star would have one third of the Sun's luminosity ( L ☉ ) and a surface temperature of 6,500–8,500 kelvins . The fact that red dwarfs and other low-mass stars still remain on the main sequence when more massive stars have moved off the main sequence allows the age of star clusters to be estimated by finding

6279-732: The main standards to the modern day. There have been negligible changes in the red dwarf spectral sequence since 1991. Additional red dwarf standards were compiled by Henry et al. (2002), and D. Kirkpatrick has recently reviewed the classification of red dwarfs and standard stars in Gray & Corbally's 2009 monograph. The M dwarf primary spectral standards are: GJ 270 (M0V), GJ 229A (M1V), Lalande 21185 (M2V), Gliese 581 (M3V), Gliese 402 (M4V), GJ 51 (M5V), Wolf 359 (M6V), van Biesbroeck 8 (M7V), VB 10 (M8V), LHS 2924 (M9V). Many red dwarfs are orbited by exoplanets , but large Jupiter -sized planets are comparatively rare. Doppler surveys of

6370-502: The mass at which the stars move off the main sequence. This provides a lower limit to the age of the Universe and also allows formation timescales to be placed upon the structures within the Milky Way , such as the Galactic halo and Galactic disk . All observed red dwarfs contain "metals" , which in astronomy are elements heavier than hydrogen and helium. The Big Bang model predicts that

6461-456: The metal-poor environment of the early universe. As giant stars end their short lives in supernova explosions, they spew out the heavier elements needed to form smaller stars. Therefore, dwarfs became more common as the universe aged and became enriched in metals. While the basic scarcity of ancient metal-poor red dwarfs is expected, observations have detected even fewer than predicted. The sheer difficulty of detecting objects as dim as red dwarfs

6552-439: The minimum mass a red dwarf must have to eventually evolve into a red giant is 0.25  M ☉ ; less massive objects, as they age, would increase their surface temperatures and luminosities becoming blue dwarfs and finally white dwarfs . The less massive the star, the longer this evolutionary process takes. A 0.16  M ☉ red dwarf (approximately the mass of the nearby Barnard's Star ) would stay on

6643-486: The name Proxima Centauri ( / ˈ p r ɒ k s ɪ m ə s ɛ n ˈ t ɔːr aɪ / ) for α Centauri C . On 10 August 2018, the IAU approved the name Toliman ( / ˈ t ɒ l ɪ m æ n / ) for α Centauri B . During the 19th century, the northern amateur popularist E.H. Burritt used the now-obscure name Bungula ( / ˈ b ʌ ŋ ɡ juː l ə / ). Its origin is not known, but it may have been coined from

6734-429: The name has not been used in the literature, as it is not a claimed discovery. Additional planets may exist in the Alpha Centauri system, either orbiting Alpha Centauri A or Alpha Centauri B individually, or in large orbits around Alpha Centauri AB. Because both stars are fairly similar to the Sun (for example, in age and metallicity ), astronomers have been especially interested in making detailed searches for planets in

6825-443: The north, giving an overall motion of 3686 mas/y in a direction 11° north of west. The motion of the centre of mass is about 6.1  arcmin each century, or 1.02 ° each millennium. The speed in the western direction is 23.0 km/s (14.3 mi/s) and in the northerly direction 4.4 km/s (2.7 mi/s). Using spectroscopy the mean radial velocity has been determined to be around 22.4 km/s (13.9 mi/s) towards

6916-425: The ratio of the solar mass to their masses; thus, a 0.1  M ☉ red dwarf may continue burning for 10 trillion years. As the proportion of hydrogen in a red dwarf is consumed, the rate of fusion declines and the core starts to contract. The gravitational energy released by this size reduction is converted into heat, which is carried throughout the star by convection. According to computer simulations,

7007-470: The relative places of the stars from a binary star ephemeris . Others, like D. Pourbaix (2002), have regularly refined the precision of new published orbital elements. Robert T. A. Innes discovered Proxima Centauri in 1915 by blinking photographic plates taken at different times during a proper motion survey. These showed large proper motion and parallax similar in both size and direction to those of α Centauri AB, which suggested that Proxima Centauri

7098-466: The same term [REDACTED] This disambiguation page lists articles associated with the title Toliman . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Toliman_(disambiguation)&oldid=888098618 " Categories : Disambiguation pages Place name disambiguation pages Hidden categories: Short description

7189-409: The smallest have radii about 9% that of the Sun , with masses about 7.5% that of the Sun . These red dwarfs have spectral types of L0 to L2. There is some overlap with the properties of brown dwarfs , since the most massive brown dwarfs at lower metallicity can be as hot as 3,600 K and have late M spectral types. Definitions and usage of the term "red dwarf" vary on how inclusive they are on

7280-446: The star, announced in 2022. The existence of Proxima c ( α Centauri Cc ) , a mini-Neptune 1.5  AU away discovered in 2019, is controversial. α Centauri A may have a Neptune-sized planet in the habitable zone, though it is not yet known with certainty to be planetary in nature and could be an artifact of the discovery mechanism. α Centauri B has no known planets: Planet α Cen Bb , purportedly discovered in 2012,

7371-406: The star, avoiding helium buildup at the core, thereby prolonging the period of fusion. Low-mass red dwarfs therefore develop very slowly, maintaining a constant luminosity and spectral type for trillions of years, until their fuel is depleted. Because of the comparatively short age of the universe , no red dwarfs yet exist at advanced stages of evolution. The term "red dwarf" when used to refer to

7462-436: The star. Certain special assumptions, such as considering that the Alpha Centauri pair may have initially formed with a wider separation and later moved closer to each other (as might be possible if they formed in a dense star cluster ), would permit an accretion-friendly environment farther from the star. Bodies around Alpha Centauri A would be able to orbit at slightly farther distances due to its stronger gravity. In addition,

7553-417: The stars were permanently fixed on the celestial sphere , as stated in the works of the philosopher Aristotle. In 1718, Edmond Halley found that some stars had significantly moved from their ancient astrometric positions. In the 1830s, Thomas Henderson discovered the true distance to α Centauri by analysing his many astrometric mural circle observations. He then realised this system also likely had

7644-743: The years, but settled down somewhat since the early 1990s. Part of this is due to the fact that even the nearest red dwarfs are fairly faint, and their colors do not register well on photographic emulsions used in the early to mid 20th century. The study of mid- to late-M dwarfs has significantly advanced only in the past few decades, primarily due to development of new astrographic and spectroscopic techniques, dispensing with photographic plates and progressing to charged-couple devices (CCDs) and infrared-sensitive arrays. The revised Yerkes Atlas system (Johnson & Morgan, 1953) listed only two M type spectral standard stars: HD 147379 (M0V) and HD 95735/ Lalande 21185 (M2V). While HD 147379

7735-413: Was also used, but sometimes it also included stars of spectral type K. In modern usage, the definition of a red dwarf still varies. When explicitly defined, it typically includes late K- and early to mid-M-class stars, but in many cases it is restricted just to M-class stars. In some cases all K stars are included as red dwarfs, and occasionally even earlier stars. The most recent surveys place

7826-520: Was found orbiting the red dwarf OGLE-2005-BLG-390L ; it lies 390 million kilometres (2.6 AU) from the star and its surface temperature is −220 °C (53.1 K; −364.0 °F). In 2007, a new, potentially habitable exoplanet, Gliese 581c , was found, orbiting Gliese 581 . The minimum mass estimated by its discoverers (a team led by Stephane Udry ) is 5.36  M E . The discoverers estimate its radius to be 1.5 times that of Earth ( R 🜨 ). Since then Gliese 581d , which

7917-416: Was later disproven, and no other planet has yet been confirmed. α Centauri ( Latinised to Alpha Centauri ) is the system's designation given by J. Bayer in 1603. It belongs to the constellation Centaurus , named after the half human, half horse creature in Greek mythology. Hercules accidentally wounded the centaur and placed him in the sky after his death. Alpha Centauri marks the right front hoof of

8008-466: Was little agreement among the standards. As later cooler stars were identified through the 1980s, it was clear that an overhaul of the red dwarf standards was needed. Building primarily upon the Boeshaar standards, a group at Steward Observatory (Kirkpatrick, Henry, & McCarthy, 1991) filled in the spectral sequence from K5V to M9V. It is these M type dwarf standard stars which have largely survived as

8099-514: Was not considered a standard by expert classifiers in later compendia of standards, Lalande 21185 is still a primary standard for M2V. Robert Garrison does not list any "anchor" standards among the red dwarfs, but Lalande 21185 has survived as a M2V standard through many compendia. The review on MK classification by Morgan & Keenan (1973) did not contain red dwarf standards. In the mid-1970s, red dwarf standard stars were published by Keenan & McNeil (1976) and Boeshaar (1976), but there

8190-526: Was not fully acknowledged at first. (The distance of Alpha Centauri from the Earth is now reckoned at 4.396  light-years or 4.159 × 10  km.) Later, John Herschel made the first micrometrical observations in 1834. Since the early 20th century, measures have been made with photographic plates . By 1926, William Stephen Finsen calculated the approximate orbit elements close to those now accepted for this system. All future positions are now sufficiently accurate for visual observers to determine

8281-415: Was thought to account for this discrepancy, but improved detection methods have only confirmed the discrepancy. The boundary between the least massive red dwarfs and the most massive brown dwarfs depends strongly on the metallicity. At solar metallicity the boundary occurs at about 0.07  M ☉ , while at zero metallicity the boundary is around 0.09  M ☉ . At solar metallicity,

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