Mira 20880 224847102 2008-07-10T18:03:56Z Kbdankbot 6505923 Robot - move category per [[WP:CFD|CFD]] [[Wikipedia:Categories for discussion/Log/2008 July 2|2008 July 2]] {{otheruses}} {{Starbox begin |name=Mira }} {{Starbox image | image=[[Image:Mira 1997.jpg|250px]] | caption=Mira as seen by [[Hubble Space Telescope|Hubble]]. ''[[NASA]] image''.}} {{Starbox observe | epoch=[[J2000.0]] | constell=[[Cetus]] | ra={{RA|02|19|20.7927}}<ref name="SIMBAD">{{cite web | url=http://simbad.u-strasbg.fr/simbad/sim-id?protocol=html&Ident=V*+omi+Cet | title=V* omi Cet -- Variable Star of Mira Cet type | work=SIMBAD | publisher=Centre de Données astronomiques de Strasbourg | accessdate=2006-08-10 }}</ref> | dec={{DEC|-02|58|39.513}}<ref name="SIMBAD"/> | appmag_v=2.0 ''to'' 10.1 }} {{Starbox character | class=M7&nbsp;IIIe<ref>{{cite journal | last=Castelaz | first=Michael W. | coauthors=Luttermoser, Donald G. | title=Spectroscopy of Mira Variables at Different Phases. | journal=The Astronomical Journal | year=1997 | volume=114 | pages=1584–1591 | url=http://adsabs.harvard.edu/abs/1997AJ....114.1584C | accessdate=2007-12-10 | doi=10.1086/118589 }}</ref> | b-v=+1.53<ref name="apj87">{{cite journal | last=Celis S. | first=L. | title=Red variable stars. I - UBVRI photometry and photometric properties | journal=Astronomical Journal | year=1982 | volume=87 | pages=1791–1802 | url=http://adsabs.harvard.edu/abs/1982AJ.....87.1791C | accessdate=2007-12-10 | doi=10.1086/113268 }}</ref> | u-b=+0.08<ref name="apj87"/> | variable=[[Mira variable]] }} {{Starbox astrometry | radial_v=+63.8<ref name="SIMBAD"/> | prop_mo_ra=10.33<ref name="SIMBAD"/> | prop_mo_dec=-239.48<ref name="SIMBAD"/> | parallax=7.79 | p_error=1.07 | parallax_footnote=<ref name="SIMBAD"/> | absmag_v=0.93 }} {{Starbox detail | age=6&times;10<sup>9</sup><ref name=apj275/> | metal= | mass=1.18<ref name=apj275>{{cite journal | last=Wyatt | first=S. P. | coauthors=Cahn, J. H. | title=Kinematics and ages of Mira variables in the greater solar neighborhood | journal=Astrophysical Journal, Part 1 | year=1983 | volume=275 | pages=225–239 | url=http://adsabs.harvard.edu/abs/1983ApJ...275..225W | accessdate=2007-12-17 | doi=10.1086/161527 }}</ref> | radius=332&ndash;402<ref name=aaa421>{{cite journal | last=Woodruff | first=H. C. | coauthors=Eberhardt, M.; Driebe, T.; Hofmann, K.-H.; Ohnaka, K.; Richichi, A.; Schert, D.; Schöller, M.; Scholz, M.; Weigelt, G.; Wittkowski, M.; Wood, P. R. | title=Interferometric observations of the Mira star o Ceti with the VLTI/VINCI instrument in the near-infrared | journal=Astronomy & Astrophysics | year=2004 | volume=421 | pages=703–714 | url=http://www.eso.org/~mwittkow/publications/conferences/SPIECWo5491199.pdf | accessdate=2007-12-07 | doi=10.1051/0004-6361:20035826 }}</ref> | rotation= | luminosity=8400&ndash;9360<ref name=aaa421/> | temperature=2918&ndash;3192<ref name=aaa421/> }} {{Starbox catalog | names=Stella Mira, Collum Ceti, Wonderful Star,<ref>{{cite book | first=Richard H. | last=Allen | year=1963 | title=Star Names: Their Lore and Meaning | publisher=Dover Publications | location=New York | isbn=0486210790 }}</ref> Omicron Ceti, 68 Ceti, [[Harvard Revised catalogue|HR 681]], [[Bonner Durchmusterung|BD &minus;03°353]], [[Henry Draper catalogue|HD 14386]], [[Luyten Two-Tenths catalogue|LTT 1179]], [[Smithsonian Astrophysical Observatory|SAO 129825]], [[Hipparcos catalogue|HIP 10826]].<ref name="SIMBAD"/> }} {{Starbox end}} '''Mira''', {{pronEng|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%. ==Observation history== Evidence that the variability of Mira was known in ancient [[History of China|China]], [[Babylon]] or [[Ancient Greece|Greece]] is at best only circumstantial.<ref>{{cite journal | last=Wilk | first=Stephen R | title=Mythological Evidence for Ancient Observations of Variable Stars | journal=The Journal of the American Association of Variable Star Observers | year=1996 | volume=24 | issue=2 | pages=129–133 | url=http://adsabs.harvard.edu/abs/1996JAVSO..24..129W | accessdate=2007-12-07 }}</ref> 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 (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 [[Apparent magnitude|magnitude]], then by October had faded from view. Fabricius assumed it was a nova, but then saw it again on [[February 16]], [[1609]] <ref> {{Citation | last = Hoffleit | first = Dorrit | title = History of Mira's Discovery | url = http://www.aavso.org/vstar/vsots/mirahistory.shtml | accessdate = 2007-08-16}} </ref>. 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). 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. ==System== ===Component A=== 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 core. 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]].<ref name=pogge>{{cite web | last=Pogge | first=Richard | date=[[January 21]], [[2006]] | url=http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit2/lowmass.html | title=Lecture 16: The Evolution of Low-Mass Stars | publisher=Ohio State University | accessdate=2007-12-11 }}</ref> 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 a star's evolution is called the [[horizontal branch]].<ref name=pogge/> 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),<ref name=pogge/> and Mira A is currently at this phase of its evolution.<ref name=lopez/> [[Image:Mira the star.jpg|Mira as seen from the Earth|thumb|200px]] Once the temperature above Mira's helium burning shell rose to about 10<sup>7</sup>K, 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&nbsp;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.<ref>{{cite book | first=C. W. H. | last=De Loore | coauthors=Doom, C | year=1992 | title=Structure and Evolution of Single and Binary Stars | publisher=Springer | id=ISBN 0792317688 }}</ref> 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&ndash;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.<ref name=lopez>{{cite conference | last=Lopez | first=B. | title=AGB and post-AGB stars at high angular resolution | booktitle=Proceedings IAU Symposium #191: Asymptotic Giant Branch Stars | year=1999 | pages=409 | url=http://adsabs.harvard.edu/abs/1999IAUS..191..409L | accessdate = 2007-12-11 }}</ref> ===Variability=== Mira A is a well-known example of a category of [[variable star]]s known as [[Mira variable]]s, which are named after this star. It&mdash;and the other 6000{{Fact|date=December 2007}} or so known stars of this class&mdash;are all [[red giant]]s 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. In the particular case of Mira, its increases in brightness take it up to about [[Apparent magnitude|magnitude]] 3.5 on average, placing it among the [[List of stars in Cetus|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 [[solar radiation|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..<ref> {{Citation | last = Braune | first = Werner | title = Bundesdeutsche Arbeitsgemeinschaft für Veränderliche Sterne | url=http://www.bav-astro.de/index_e.html | accessdate = 2007-08-16}}</ref> ===Mass loss=== [[Image:Mira-uv-bow-shock-tail-vertical.jpg|150px|right|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 <ref>{{cite journal |last=Martin |first=Christopher |journal=Nature |volume=448 |title=A turbulent wake as a tracer of 30,000 years of Mira's mass loss history |doi=10.1038/nature06003 |date=[[August 17]], [[2007]] |pages=780–783 |access-date=2007-12-11}}</ref><ref>Minkel, JR. [http://www.sciam.com/article.cfm?articleID=6AE74053-E7F2-99DF-353EB7B9AE43FCF6&chanID=sa007&ec=su_astro "Shooting Bullet Star Leaves Vast Ultraviolet Wake"], "The Scientific American", [[August 15]] [[2007]]. Accessed [[August 21]] [[2007]].</ref>. It is thought that a hot [[bow_shock|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 <ref>{{cite journal |last=Wareing |first=Christopher |journal=Astrophysical Journal |volume=670 |title=It's a wonderful tail: the mass-loss history of Mira |doi= 10.1086/524407 |date=[[November 6]], [[2007]] |pages=L125–L129}}</ref><ref>{{cite web |url=http://www.galex.caltech.edu/MEDIA/2007-04/images.html |title=GALEX finds link between big and small stellar blasts |accessdate=2007-08-16 |last=Clavin |first=W. |year=2007 |month=August |day=15 |publisher=California Institute of Technology}}</ref>. The tail consists of material stripped from the head of the bow-wave, which is also visible in ultra-violet observations. ===Component B=== {{main|Mira B}} The companion star was resolved by the [[Hubble Space Telescope]] in 1995, when it was 70 [[astronomical unit]]s from the primary; results were announced in 1997. The HST ultraviolet images and later X-ray images by the [[Chandra X-ray Observatory|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. In 2007, observations showed a [[protoplanetary disc]] around the companion, Mira B. This disc is being accreted from material in the [[stellar wind|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 mass]]es and [[spectral type]] K, instead of a [[white dwarf]] as previously believed <ref> {{Citation | last = Than | first = Ker | title = Dying star's dust helping to build new planets | url = http://www.msnbc.msn.com/id/16564325/ | accessdate = 2007-08-16}} </ref>. ==References== {{Reflist}} ==See also== *[[Stars and planetary systems in fiction#Mira (Omicron Ceti)|Mira in fiction]] ==External links== {{commons|Mira Ceti}} *[http://www.nasa.gov/mission_pages/galex/20070815/ Mira – Bizarre Star at NASA] *[http://www.aavso.org/vstar/vsots/mirahistory.shtml History of Mira's Discovery] at [[AAVSO]] *[http://news.bbc.co.uk/1/hi/sci/tech/6947607.stm Mira has tail nearly 13 light years in length (BBC)] *[http://www.galex.caltech.edu/MEDIA/2007-04/ Speeding Bullet Star Leaves Enormous Streak Across Sky] at [[Caltech]] *[[Astronomy Picture of the Day]]:<br>[http://antwrp.gsfc.nasa.gov/apod/ap981011.html 1998-10-11], [http://antwrp.gsfc.nasa.gov/apod/ap010121.html 2001-01-21], [http://antwrp.gsfc.nasa.gov/apod/ap060722.html 2006-07-22], [http://antwrp.gsfc.nasa.gov/apod/ap070221.html 2007-02-21], [http://antwrp.gsfc.nasa.gov/apod/ap070817.html 2007-08-17] *{{web cite|url=http://www.daviddarling.info/encyclopedia/M/Mira.html|title=Mira (Omicron Ceti)|work='''The Encyclopedia of Astrobiology, Astronomy, and Spaceflight'''|accessdate=June 22|accessyear=2006}} *{{web cite|url=http://www.alcyone.de/SIT/mainstars/SIT000348.htm |title=Mira|work=Alcyone Ephemeris|accessdate=2006-08-25}} *{{web cite|url=http://www.eso.org/~mwittkow/publications/conferences/SPIECWo5491199.pdf|title=Interferometric observations of the Mira star o Ceti with the VLTI/VINCI instrument in the near-infrared}} *Robert Burnham Jr., ''Burnham's Celestial Handbook'', Vol. 1, (New York: Dover Publications, Inc., 1978), 634. *James Kaler, ''The Hundred Greatest Stars'', (New York: Copernicus Books, 2002), 121. *[http://seds.org/~spider/Spider/Vars/mira.html SEDS article] * A [http://www.bav-astro.de/sterne/cetmira.shtml recent lightcurve] of Mira from the BAV. [[Category:Bayer objects|Ceti, Omicron]] [[Category:Binary stars]] [[Category:Cetus constellation]] [[Category:Mira variables]] [[Category:M-type giants]] [[Category:Stars with proper names]] [[als:Mira (Stern)]] [[cs:Mira]] [[da:Mira]] [[de:Mira (Stern)]] [[es:Mira (estrella)]] [[eo:Omikron Baleno]] [[fr:Omicron Ceti]] [[ko:미라 (항성)]] [[it:Mira (stella)]] [[lb:Mira (Stär)]] [[nl:Mira (ster)]] [[ja:ミラ]] [[no:Mira]] [[pl:Mira Ceti]] [[pt:Mira (estrela)]] [[ru:Мира (звезда)]] [[sk:Mira]] [[fi:Mira]] [[sv:Mira]] [[tr:Mira Ceti]] [[zh:米拉]]