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Encyclopedia > Mira
Mira

Mira as seen by Hubble. NASA image.
Observation data
Epoch J2000.0
Constellation
(pronunciation)
Cetus
Right ascension 02h 19m 20.7927s[1]
Declination -02° 58′ 39.513″[1]
Apparent magnitude (V) 2.0 to 10.1
Characteristics
Spectral type M7 IIIe[2]
U-B color index +0.08[3]
B-V color index +1.53[3]
Variable type Mira variable
Astrometry
Radial velocity (Rv) +63.8[1] km/s
Proper motion (μ) RA: 10.33[1] mas/yr
Dec.: -239.48[1] mas/yr
Parallax (π) 7.79 ± 1.07[1] mas
Distance approx. 420 ly
(approx. 130 pc)
Absolute magnitude (MV) 0.93
Details
Mass 1.18[4] M
Radius 332–402[5] R
Luminosity 8400–9360[5] L
Temperature 2918–3192[5] K
Age 6×109[4] years
Other designations
Stella Mira, Collum Ceti, Wonderful Star,[6] Omicron Ceti, 68 Ceti, HR 681, BD −03°353, HD 14386, LTT 1179, SAO 129825, HIP 10826.[1]

Mira, pronounced /ˈmaɪrə/, also known as Omicron Ceti (or ο Ceti / ο Cet), is a red giant star estimated 200-400 light years away in the constellation Cetus. Mira is a binary star, consisting of the red giant Mira A along with Mira B. Mira A is also an oscillating variable star and was the first non-supernova variable star discovered, with the possible exception of Algol. Apart from the unusual Eta Carinae, Mira is the brightest periodic variable in the sky that is not visible to the naked eye for part of its cycle. Its distance is uncertain; pre-Hipparcos estimates centered around 220 light-years,(1) while Hipparcos data suggests a distance of 418 light-years, albeit with a margin of error of ~14%. Look up mira in Wiktionary, the free dictionary. ... Image File history File links Mira_1997. ... The Hubble Space Telescope (HST) is a telescope in orbit around the Earth, named after astronomer Edwin Hubble. ... The National Aeronautics and Space Administration (NASA) (IPA [ˈnæsÉ™]) is an agency of the United States government, responsible for the nations public space program. ... In astronomy, an epoch is a moment in time for which celestial coordinates or orbital elements are specified. ... It has been suggested that this article or section be merged into Julian epoch. ... This article is about the star grouping. ... From the dawn of time, poop observed the sky and grouped stars into patterns or constellations. ... Cetus (pronounced , latinized form of Ancient Greek κῆτος - kÄ“tos, “whale, any sea-monster or huge fish”) is a constellation of the southern sky, in the region known as the Water, near other watery constellations like Aquarius, Pisces, and Eridanus. ... Equatorial Coordinates Right ascension (abbrev. ... In astronomy, declination (abbrev. ... The apparent magnitude (m) of a star, planet or other celestial body is a measure of its apparent brightness as seen by an observer on Earth. ... In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequently refined in terms of other characteristics. ... In astronomy, the color index is a simple numerical expression that determines the color of an object, which in the case of a star gives its temperature. ... In astronomy, the color index is a simple numerical expression that determines the color of an object, which in the case of a star gives its temperature. ... This article or section contains a plot summary that is overly long or excessively detailed. ... Mira variables, named after the star Mira (IPA: ), are a class of pulsating variable stars characterized by very red colors, pulsation periods longer than 100 days, and light amplitudes greater than one magnitude. ... Illustration of the use of optical wavelength interferometry to determine precise positions of stars. ... Radial velocity is the velocity of an object in the direction of the line of sight. ... kilometre per second is an SI derived unit of both speed (scalar) and velocity (vector), signified by the symbol km/s or km s-1. ... The proper motion of a star is the motion of the position of the star in the sky (the change in direction in which we see it, as opposed to the radial velocity) after eliminating the improper motions of the stars, which affect their measured coordinates but are not real... A milliarcsecond (m, mas) , or a thoundsanth of an arcsecond. ... A year (from Old English gÄ“r) is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... A milliarcsecond (m, mas) , or a thoundsanth of an arcsecond. ... A year (from Old English gÄ“r) is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... For other uses, see Parallax (disambiguation). ... A milliarcsecond (m, mas) , or a thoundsanth of an arcsecond. ... Distance is a numerical description of how far apart objects are at any given moment in time. ... A light-year or lightyear (symbol: ly) is a unit of measurement of length, specifically the distance light travels in vacuum in one year. ... A parsec is the distance from the Earth to an astronomical object which has a parallax angle of one arcsecond. ... In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us, in the absence of interstellar extinction. ... For other uses, see Mass (disambiguation). ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... This article is about an authentication, authorization, and accounting protocol. ... In astronomy, the solar radius is a unit of length used to express the size of stars and larger objects such as galaxies. ... This article does not cite any references or sources. ... The solar luminosity, , is a unit of luminosity (power emitted in the form of photons) conventionally used by astronomers to give the luminosities of stars. ... For other uses, see Temperature (disambiguation). ... For other uses, see Kelvin (disambiguation). ... This article is about the astronomical object. ... A year (from Old English gÄ“r) is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... A star catalogue, or star catalog, is an astronomical catalog that lists stars. ... In astronomy, many stars are referred to simply by catalogue numbers. ... In astronomy, many stars are referred to simply by catalogue numbers. ... The Henry Draper Catalogue is an astronomy catalogue with astrometric and spectroscopic data about more than 225,000 stars. ... In astronomy, many stars are referred to simply by catalogue numbers. ... The Smithsonian Astrophysical Observatory (SAO) is a research institute of the Smithsonian Institution headquartered in Cambridge, Massachusetts, where it is joined with the Harvard College Observatory (HCO) to form the Harvard-Smithsonian Center for Astrophysics (CfA). ... The Hipparcos and Tycho Catalogues (Tycho-1) are the primary products of the European Space Agencys astrometric mission, Hipparcos. ... Look up Ο, ο in Wiktionary, the free dictionary. ... According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giant stars. ... This article is about the astronomical object. ... A light year, abbreviated ly, is the distance light travels in one year: roughly 9. ... This article is about the star grouping. ... Cetus (pronounced , latinized form of Ancient Greek κῆτος - kÄ“tos, “whale, any sea-monster or huge fish”) is a constellation of the southern sky, in the region known as the Water, near other watery constellations like Aquarius, Pisces, and Eridanus. ... For the band of the same name, see: Binary Star (band) Hubble image of the Sirius binary system, in which Sirius B can be clearly distinguished (lower left). ... According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giant stars. ... Mira B Mira B, also known as VZ Ceti, is the white dwarf companion to the variable star Mira. ... This article or section contains a plot summary that is overly long or excessively detailed. ... For other uses, see Supernova (disambiguation). ... It has been suggested that ALGOL object code be merged into this article or section. ... Eta Carinae (η Carinae or η Car) is a highly luminous hypergiant double star. ... Hipparcos (for High Precision Parallax Collecting Satellite) was an astrometry mission of the European Space Agency (ESA) dedicated to the measurement of stellar parallax and the proper motions of stars. ... Alternate cover Tour Edition Cover Light Years is also the American name of the Rene Laloux animated film Gandahar. ... The top portion of this graphic depicts probability densities (for a binomial distribution) that show the relative likelihood that the true percentage is in a particular area given a reported percentage of 50%. The bottom portion of this graphic shows the margin of error, the corresponding zone of 95% confidence. ...

Contents

Observation history

Evidence that the variability of Mira was known in ancient China, Babylon or Greece is at best only circumstantial.[7] What is certain is that the variability of Mira was recorded by the astronomer David Fabricius beginning on August 3, 1596. Observing the planet Mercury, he needed a reference star for comparing positions and picked a previously unremarked third-magnitude star nearby. By August 21, however, it had increased in brightness by one magnitude, then by October had faded from view. Fabricius assumed it was a nova, but then saw it again on February 16, 1609 [8]. For other uses, see Babylon (disambiguation). ... David and Johannes Fabricius were father and son astronomers from Frisia. ... is the 215th day of the year (216th in leap years) in the Gregorian calendar. ... Events February 5 - 26 catholics crucified in Nagasaki, Japan. ... This article is about the planet. ... is the 233rd day of the year (234th in leap years) in the Gregorian calendar. ... The apparent magnitude (m) of a star, planet or other celestial body is a measure of its apparent brightness as seen by an observer on Earth. ... is the 47th day of the year in the Gregorian calendar. ... // Events April 4 – King of Spain signs an edit of expulsion of all moriscos from Spain April 9 – Spain recognizes Dutch independence May 23 - Official ratification of the Second Charter of Virginia. ...


Eventually, Johann Holwarda determined a period of the star's reappearances, eleven months; Johannes Hevelius was observing it at the same time and named it "Mira" (meaning "wonderful, astonishing") in 1662's Historiola Mirae Stellae, for it acted like no other known star. Ismail Bouillaud then estimated its period at 333 days, less than one day off the modern value of 332 days (and perfectly forgivable, as Mira is known to vary slightly in period, and may even be slowly changing over time). Johannes Hevelius Johannes Hevelius (Latin), also called Johann Hewelke, Johannes Höwelcke or Johannes Hewel (in German), or Jan Heweliusz (in Polish), (born January 28, 1611 – died January 28, 1687), was a councillor and mayor in Danzig (Gdańsk). ... Ismael Bullialdus Ismael Bullialdus (Boulliaud, Boulliau) (September 28, 1605 - November 25, 1694) was a French astronomer. ...


There is considerable speculation as to whether Mira had been observed prior to Fabricius. Certainly Algol's history (known for certain as a variable only in 1667, but with legends and such dating back to antiquity showing that it had been observed with suspicion for millennia) suggests that Mira might have been known too. Karl Manitius, a translator of Hipparchus' Commentary on Aratus, has suggested that certain lines from that second century text may be about Mira. The other pre-telescopic Western catalogs of Ptolemy, al-Sufi, Ulugh Beg, and Tycho Brahe turn up no mentions, even as a regular star. There are three observations from Chinese and Korean archives, in 1596, 1070, and the same year when Hipparchus would have made his observation (134 BC) that are suggestive, but the Chinese practice of pinning down observations no more precisely than within a given Chinese constellation makes it difficult to be sure. It has been suggested that ALGOL object code be merged into this article or section. ... For the Athenian tyrant, see Hipparchus (son of Pisistratus). ... This article is about the geographer, mathematician and astronomer Ptolemy. ... Al Sufi from The Depiction of Celestial Constellations Abd Al-Rahman Al Sufi (December 7, 903 – May 25, 986) was a Persian astronomer also known as Abd ar-Rahman as-Sufi, or Abd al-Rahman Abu al-Husain, and known in the west as Azophi. ... Ulugh Beg, here depicted on a Soviet stamp, was one of Islams greatest astronomers during the Middle Ages. ... This article is about the astronomer. ... Chinese constellations are different from the western constellations, due to the independent development of ancient Chinese astronomy. ...


System

Component A

Mira as seen from the Earth

Mira A generated energy by nuclear fusion of hydrogen to form helium at its core. Once the supply of hydrogen at the core was exhausted, fusion of hydrogen continued along a shell surrounding the inert helium shell. This shell generated more energy from fusion than did the core, so the luminosity of Mira A increases. However, at the same time, the outer atmosphere of Mira A expanded to many times its original size, producing a red giant.[9] The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing fusion power. ... This article is about the chemistry of hydrogen. ... General Name, symbol, number helium, He, 2 Chemical series noble gases Group, period, block 18, 1, s Appearance colorless Standard atomic weight 4. ... According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giant stars. ...


As additional helium was generated by the hydrogen-burning shell, the dormant helium core of Mira A steadily increased in mass. Once the core reached a temperature and pressure sufficient to begin burning helium, Mira A underwent a runaway process called the helium flash. This initiates the fusion of helium in the core, producing an ash of carbon and oxygen. Gradually the core expanded and cooled, and decreased energy was generated from hydrogen-burning. This caused the luminosity of the star to decrease, while the outer atmosphere shrank and increased in temperature. This stage of the star's evolution is called the horizontal branch.[9] A Helium flash is the sudden beginning of helium burning in the core of intermediate mass stars, or on the surface of an accreting white dwarf star. ... The horizontal branch (HB) is a stage of stellar evolution which immediately follows the red giant branch. ...


When the supply of helium at the core became exhausted, a new helium-burning shell forms around the inactive core of carbon and oxygen. Once more Mira A began to expand, increasing in luminosity while the surface temperature decreased. This stage is known as the Asymptotic Giant Branch (AGB),[9] and Mira A is currently at this phase of its evolution.[10] A period of Stellar evolution undertaken by all low to intermediate mass stars (0. ...


Once the temperature above Mira's helium burning shell rose to about 107K, hydrogen became ignited along a shell at that radius. However, because energy is now less readily transported through the hydrogen burning region, pressure builds up between the layers. This causes the hydrogen burning layer to rise until the fusion is shut off by lower temperatures. Mira then contracts and the hydrogen layer re-ignites. The result is an instability in Mira known as the thermally pulsing AGB phase. Each pulse lasts a decade or more, and on the order of 10,000 years passes between each pulse. With every pulse cycle Mira increases in luminosity and the pulses grow stronger. This is also causing dynamic instability in Mira, resulting in dramatic changes in luminosity and size over shorter, irregular time periods.[11]


The overall shape of Mira A has been observed to change, exhibiting pronounced departures from symmetry. These appear to be caused by bright spots on the surface that evolve their shape on time scales of 3–14 months. Observations of Mira A in the ultraviolet band by the Hubble Space Telescope have shown a plume-like feature pointing toward the companion star.[10] For other uses, see Ultraviolet (disambiguation). ... The Hubble Space Telescope (HST) is a telescope in orbit around the Earth, named after astronomer Edwin Hubble. ...


Variability

Mira A is a well-known example of a category of variable stars known as Mira variables, which are named after this star. It—and the other 6000[citation needed] or so known stars of this class—are all red giants whose surfaces oscillate in such a way as to increase and decrease in brightness over periods ranging from about 80 days to more than 1000. This article or section contains a plot summary that is overly long or excessively detailed. ... Mira variables, named after the star Mira (IPA: ), are a class of pulsating variable stars characterized by very red colors, pulsation periods longer than 100 days, and light amplitudes greater than one magnitude. ... According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giant stars. ...


In the particular case of Mira, its increases in brightness take it up to about magnitude 3.5 on average, placing it among the brighter stars in the Cetus constellation. Individual cycles vary too; well-attested maxima go as high as magnitude 2.0 in brightness and as low as 4.9, a range almost 15 times in brightness, and there are historical suggestions that the real spread may be three times this or more. Minima range much less, and have historically been between 8.6 and 10.1, a factor of four times in luminosity. The total swing in brightness from absolute maximum to absolute minimum (two events which did not occur on the same cycle) is 1700 times. Interestingly, since Mira emits the vast majority of its radiation in the infrared, its variability in that band is only about two magnitudes.(2) The shape of its light curve is of an increase over about 100 days, and a return twice as long..[12] The apparent magnitude (m) of a star, planet or other celestial body is a measure of its apparent brightness as seen by an observer on Earth. ... This is the list of notable stars in the constellation Cetus, sorted by decreasing brightness. ... Solar irradiance spectrum at top of atmosphere. ... For other uses, see Infrared (disambiguation). ... In astronomy, a light curve is a graph of light intensity as a function of time. ...


Mass loss

Ultraviolet mosaic of Mira's bow shock and tail

Ultra-violet studies of Mira by NASA's Galaxy Evolution Explorer (Galex) space telescope have revealed that it sheds a trail of material from the outer envelope, creating a tail 13 light-years in length, formed over tens of thousands of years [13][14]. It is thought that a hot bow-wave of compressed plasma/gas is the cause of the tail; the bow-wave is a result of the interaction of the stellar wind from Mira A with gas in the interstellar space, through which Mira is moving at an extremely high speed of 130 kilometres/second [15][16]. The tail consists of material stripped from the head of the bow-wave, which is also visible in ultra-violet observations. The National Aeronautics and Space Administration (NASA) (IPA [ˈnæsə]) is an agency of the United States government, responsible for the nations public space program. ... GALEX GALEX at the pre-launch tests The Galaxy Evolution Explorer is an orbiting space telescope that was launched on April 28, 2003. ...


Component B

Main article: Mira B

The companion star was resolved by the Hubble Space Telescope in 1995, when it was 70 astronomical units from the primary; results were announced in 1997. The HST ultraviolet images and later X-ray images by the Chandra space telescope show a spiral of gas rising off Mira in the direction of Mira B. The companion's orbital period around Mira is approximately 400 years. Mira B Mira B, also known as VZ Ceti, is the white dwarf companion to the variable star Mira. ... The Hubble Space Telescope (HST) is a telescope in orbit around the Earth, named after astronomer Edwin Hubble. ... The astronomical unit (AU or au or a. ... The Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. ... The orbital period is the time it takes a planet (or another object) to make one full orbit. ...


In 2007, observations showed a protoplanetary disc around the companion, Mira B. This disc is being accreted from material in the solar wind from Mira and may eventually go on to form new planets. These observations also revealed that the companion is most likely a main sequence star of around 0.7 solar masses and spectral type K, instead of a white dwarf as previously believed [17]. A protoplanetary disc (also protoplanetary disk, proplyd) is an accretion disc surrounding a T Tauri star. ... A solar wind is a stream of particles (mostly high-energy protons ~ 500 keV) which are ejected from the upper atmosphere of a star (in the case of a star other than the Earths Sun, it may be called a stellar wind instead). ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequenly refined in terms of other characteristics. ... This article or section does not adequately cite its references or sources. ...


References

  1. ^ a b c d e f g V* omi Cet -- Variable Star of Mira Cet type. SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved on 2006-08-10.
  2. ^ Castelaz, Michael W.; Luttermoser, Donald G. (1997). "Spectroscopy of Mira Variables at Different Phases.". The Astronomical Journal 114: 1584-1591. Retrieved on 2007-12-10.
  3. ^ a b Celis S., L. (1982). "Red variable stars. I - UBVRI photometry and photometric properties". Astronomical Journal 87: 1791-1802. Retrieved on 2007-12-10.
  4. ^ a b Wyatt, S. P.; Cahn, J. H. (1983). "Kinematics and ages of Mira variables in the greater solar neighborhood". Astrophysical Journal, Part 1 275: 225-239. Retrieved on 2007-12-17.
  5. ^ a b c Woodruff, H. C.; Eberhardt, M.; Driebe, T.; Hofmann, K.-H.; Ohnaka, K.; Richichi, A.; Schert, D.; Schöller, M.; Scholz, M.; Weigelt, G.; Wittkowski, M.; Wood, P. R. (2004). "Interferometric observations of the Mira star o Ceti with the VLTI/VINCI instrument in the near-infrared". Astronomy & Astrophysics 421: 703-714. Retrieved on 2007-12-07.
  6. ^ Allen, Richard H. (1963). Star Names: Their Lore and Meaning. New York: Dover Publications. ISBN 0486210790. 
  7. ^ Wilk, Stephen R (1996). "Mythological Evidence for Ancient Observations of Variable Stars". The Journal of the American Association of Variable Star Observers 24 (2): 129-133. Retrieved on 2007-12-07.
  8. ^ Hoffleit, Dorrit, History of Mira's Discovery, <http://www.aavso.org/vstar/vsots/mirahistory.shtml>. Retrieved on 16 August 2007
  9. ^ a b c Pogge, Richard (January 21, 2006). Lecture 16: The Evolution of Low-Mass Stars. Ohio State University. Retrieved on 2007-12-11.
  10. ^ a b Lopez, B. (1999). "AGB and post-AGB stars at high angular resolution". Proceedings IAU Symposium #191: Asymptotic Giant Branch Stars: 409. Retrieved on 2007-12-11. 
  11. ^ De Loore, C. W. H.; Doom, C (1992). Structure and Evolution of Single and Binary Stars. Springer. ISBN 0792317688. 
  12. ^ Braune, Werner, Bundesdeutsche Arbeitsgemeinschaft für Veränderliche Sterne, <http://www.bav-astro.de/index_e.html>. Retrieved on 16 August 2007
  13. ^ Martin, Christopher (August 17, 2007). "A turbulent wake as a tracer of 30,000 years of Mira's mass loss history". Nature 448: 780-783. doi:10.1038/nature06003.
  14. ^ Minkel, JR. "Shooting Bullet Star Leaves Vast Ultraviolet Wake", "The Scientific American", August 15, 2007. Accessed August 21, 2007.
  15. ^ Wareing, Christopher (November 6, 2007). "It's a wonderful tail: the mass-loss history of Mira". Astrophysical Journal 670: L125-L129.
  16. ^ Clavin, W. (August 2007). GALEX finds link between big and small stellar blasts. California Institute of Technology. Retrieved on 2007-08-16.
  17. ^ Than, Ker, Dying star's dust helping to build new planets, <http://www.msnbc.msn.com/id/16564325/>. Retrieved on 16 August 2007

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See also

The planetary systems of stars other than the Sun and its Solar System are a staple element in much science fiction. ...

External links

Wikimedia Commons has media related to:
Image File history File links Commons-logo. ... The American Association of Variable Star Observers (AAVSO) is an organization that collects observations of variable stars by amateur astronomers and uses them to establish light curves for each stars variation in brightness over time. ... California Institute of Technology The California Institute of Technology (commonly known as Caltech) is a private, coeducational university located in Pasadena, California, in the United States. ... The Astronomy Picture of the Day (APOD) website is a service provided by NASA and MTU (Michigan Technological University). ... is the 173rd day of the year (174th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 237th day of the year (238th in leap years) in the Gregorian calendar. ...

 
 

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