Magnetic impedance: Difference between revisions

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→References: Added See also section, and a reference to Magnetic complex impedance
 
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{{Starbox begin
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|name=Pleione, 28 Tau
}}
{{Starbox image
|image=[[File:Pleione location.png|250px]]
|caption=Pleione (indicated by the red arrow) is located just above [[Atlas (star)|Atlas]] in the East of the [[Pleiades]] cluster.
}}
{{Starbox observe
|epoch=J2000
|ra={{RA|03|49|11.2161}}<ref name="SIMBAD">
{{cite web
  |title=SIMBAD query result: PLEIONE -- Be Star
  |url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=28+Tau&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id
  |work=[[SIMBAD]]
  |publisher=[[Centre de données astronomiques de Strasbourg]]
  |accessdate=2010-06-12
}}</ref>
|dec={{DEC|24|08|12.163}} <ref name="SIMBAD" />
|appmag_v=5.048 <ref name="SIMBAD" />
|constell=[[Taurus (constellation)|Taurus]]
}}
{{Starbox character
|class=B8IVpe <ref name="HOFFLEIT">
{{cite web
  |title=Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991)
  |url=http://vizier.u-strasbg.fr/viz-bin/VizieR-S?HR%201180
  |work=[[VizieR]]
  |publisher=[[Centre de données astronomiques de Strasbourg]]
  |accessdate=2010-09-14
}}</ref>
|b-v=-0.08 <ref name="AAA34">
{{cite journal
  |last=Nicolet |first=B.
  |year=1978
  |title=Catalogue of homogeneous data in the UBV photoelectric photometric system.
  |journal=[[Astronomy and Astrophysics Supplement Series]]
  |volume=34  |pages=1–49
  |bibcode=1978A&AS...34....1N
}}</ref>
|u-b=-0.28
|variable=[[Variable star#Gamma Cassiopeiae variables|Gamma Cassiopeiae]]
}}
{{Starbox astrometry
|radial_v=4.4 <ref name="SIMBAD" />
|prop_mo_ra=18.71 <ref name="SIMBAD" />
|prop_mo_dec=-46.74 <ref name="SIMBAD" />
|parallax=8.32
|p_error=0.13
|parallax_footnote=<ref name="VANLEEUWEN">
For an in-depth discussion of [[Pleiades]] parallax measurements, see section 6.3 of {{cite journal
  |last=van Leeuwen |first=F.
  |year=2009
  |title=Parallaxes and proper motions for 20 open clusters as based on the new Hipparcos catalogue
  |journal=[[Astronomy and Astrophysics]]
  |volume=497 |issue=1 |pages=209–242
  |arxiv=0902.1039
  |bibcode=2009A&A...497..209V
  |doi=10.1051/0004-6361/200811382
}}</ref>
|absmag_v=-0.33
}}
{{Starbox detail
|mass=3.4 <ref name="KALER">
{{cite web
  |last=Kaler |first=J. B.
  |title=PLEIONE (28 Tauri)
  |publisher=University of Illinois
  |url=http://stars.astro.illinois.edu/sow/pleione.html
  |accessdate=2010-06-11
}} Kaler acknowledges a distance of 385ly to Pleione, an estimate that is likely derived from the [[Hipparcos Catalogue]] published in 1997. Any significant change in astrometric calculations could impact other calculations referenced in this article.</ref>
|radius=3.2 <ref name="KALER" />
|luminosity=190 <ref name="KALER" />
|temperature=12,000 <ref name="KALER" />
|metal=?
|rotation=329 km/s <ref name="HR1">
{{cite web
  |title=Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991)
  |url=http://vizier.u-strasbg.fr/viz-bin/VizieR-S?HR%201180
  |work=[[VizieR]]
  |publisher=[[Centre de Données astronomiques de Strasbourg]]
  |accessdate=2010-06-20
}}</ref>
|age=1.15{{e|8}}
}}
{{Starbox catalog
|names=Pleione, [[Flamsteed designation|28&nbsp;Tau]], 28&nbsp;[[Taurus constellation|Tauri]], [[Variable star designation|BU&nbsp;Tau]], BU&nbsp;[[Taurus constellation|Tauri]], [[Harvard Revised catalogue|HR]]&nbsp;1180, [[Bonner Durchmusterung|BD]]+23°&nbsp;558, [[Henry Draper Catalogue|HD]]&nbsp;23862, [[Hipparcos catalogue|HIP]]&nbsp;17851, [[Smithsonian Astrophysical Observatory Star Catalog|SAO]]&nbsp;76229, [[Boss General Catalogue|GC]]&nbsp;4587
}}
{{Starbox reference
|Simbad=HD+23862
}}
{{Starbox end}}
{{Sky|03|49|11.2161|+|24|08|12.163|100000}}
 
'''Pleione''' ('''28 Tauri''', '''BU Tauri''') is a [[binary star]] in the [[Pleiades]] [[open cluster|star cluster]] ([[Messier objects|M45]]), located roughly 390 [[light year]]s away in the [[constellation]] of [[Taurus (constellation)|Taurus]]. Pleione was not given a [[Bayer designation]], but did receive a [[Flamsteed number]]&mdash;hence its designation 28 Tauri. Since the star is located close to [[Atlas (star)|Atlas]], it's difficult for stargazers to distinguish with the naked eye, even though it's a hot [[B-type star|type B]] star 190 times more luminous than the [[Sun]]. Pleione rotates even faster than [[Achernar]] on its axis, close to its [[Stellar rotation#Equatorial bulge|breakup velocity]].
 
The brighter star of the binary pair, component A, is a classical [[Be star]] with certain distinguishing traits: periodic phase changes and a complex circumstellar environment composed of two gaseous disks at different angles to each other. Although some research on the system has been performed, stellar characteristics of the orbiting B component are not well known.<ref>See the section [[Pleione (star)#Star system|Star system]] for further information</ref> Pleione is the [[Pleiades#Brightest stars|seventh brightest]] star in the Pleiades, after [[Taygeta (star)|Taygeta]].
 
==Visibility==
[[File:Taurus constellation map.svg|thumb|left|The location of the Pleiades in the constellation [[Taurus (constellation)|Taurus]]]]
 
With an [[apparent magnitude]] of +5.05 in [[UBV photometric system|V]], the star is rather difficult to make out with the naked eye, especially since its close neighbour [[Atlas (star)|Atlas]] is 3.7 times brighter and located less than 5 [[arcminute]]s away.<ref name="NOTEATLAS" group="note">The brightness ratio of Atlas versus Pleione is derived from the [[Apparent magnitude#Calculations|formula for apparent magnitude]] and is based on their respective [[UBV photometric system|visual]] [[apparent magnitude|magnitude]]s: Atlas '''(<math>{m_A}</math>)''' at 3.62 and Pleione '''(<math>{m_P}</math>)''' at 5.05. Therefore:
:<math>\frac{m_A}{m_P}=2.512^{(5.05-3.62)}=3.73</math></ref> Beginning in October of each year, Pleione along with the rest of the cluster can be seen rising in the east in the early morning before [[dawn]].<ref name="ESOPLEIADES">
{{cite web
|last=Getsova |first=I.
|coauthors=''et al.''
|year=2002
|title=All About The Pleiades
|url=http://www.eso.org/public/outreach/eduoff/cas/cas2002/cas-projects/bulgaria_pleiades_1/
|work=Catch a Star 2002
|publisher=[[European Southern Observatory]]
|accessdate=2010-09-15
}}</ref> To see it after sunset, one will need to wait until December. By mid-February, the star is visible to virtually every inhabited region of the globe, with only those south of 66° unable to see it. Even in cities like [[Cape Town]], [[South Africa]], at the tip of the [[Africa]]n [[continent]], the star rises almost 32° above the [[horizon]]. Due to its declination of roughly +24°, Pleione is [[Circumpolar star|circumpolar]] in the [[northern hemisphere]] at latitudes greater than 66° North. Once late April arrives, the cluster can be spotted briefly in the deepening [[twilight]] of the western horizon, soon to disappear with the other setting stars.<ref name="ASTRONOMYMAGAZINE">
{{cite web
|last=Bakich |first=M. E.
|date=22 April 2009
|title=See Mercury, the Moon, and the Pleiades together in the night sky
|work=[[Astronomy (magazine)|Astronomy]]
|url=http://www.astronomy.com/asy/default.aspx?c=a&id=8172
|accessdate=2010-09-14
|quote=Don't miss a stunning sight around 9 P.M. local daylight time April 26 when a crescent Moon joins Mercury and the Pleiades in the deepening twilight.
}}</ref>
 
Pleione is classified as a [[Gamma Cassiopeiae variable|Gamma Cassiopeiae type]] [[variable star]], with brightness fluctuations that range between a 4.8 and 5.5 [[UBV photometric system|visual]] [[apparent magnitude|magnitude]].<ref name="HIC1">
{{cite web
|title=Hipparcos Input Catalogue, Version 2 (Turon+ 1993)
|url=http://vizier.u-strasbg.fr/viz-bin/VizieR-S?HIC%2017851
|work=[[VizieR]]
|publisher=[[Centre de Données astronomiques de Strasbourg]]
|accessdate=2010-06-20
}}</ref> Its [[variable star designation]] is BU Tauri. The [[SIMBAD]] astronomical database lists its [[stellar classification|spectral class]] as B8IVev,<ref name="SIMBAD"/> although the current classification recognized by many researchers is B8IVpe.<ref name="HOFFLEIT"/><ref name="MCALISTER"/><ref name="TANAKA"/> The suffix "ev" stands for ''[[Stellar classification#Spectral peculiarities|"Spectral emission that exhibits variability"]]'' whilst the suffix "pe" refers to ''[[Stellar classification#Spectral peculiarities|"Emission lines with peculiarity"]]''. In the case of Pleione, the "peculiar" emissions come from gaseous [[circumstellar disk]]s formed of material being ejected from the star.
 
There has been significant debate as to the star's actual distance from [[Earth]]. The debate revolves around the different methodologies to measure distance&mdash;[[parallax]] being the most central, but [[Photometry (astronomy)|photometric]] and [[spectroscopic]] observations yielding valuable insights as well.<ref name="VANLEEUWEN"/><ref name="ASKASTRO">
{{cite web
|last1=Allen |first1=J.
|last2=Boyd |first2=P.
|date=15 April 1997
|title=Finding Stellar Distances
|url=http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970415c.html
|work=Ask an Astrophysicist
|publisher=[[NASA]]
|accessdate=2010-09-14
|quote=A straightforward summary of the different methods used by astronomers to measure stellar distances.
}}</ref> Before the [[Hipparcos]] mission, the estimated distance for the Pleiades star cluster was around 135 [[parsecs]] or 440 [[light year]]s. However, when the [[Hipparcos Catalogue]] was published in 1997, the new parallax measurement indicated a much closer distance of about 119 ± 1.0 [[parsec|pc]] (388 ± 3.2 [[light year|ly]]), triggering substantial controversy among astronomers.<ref name="VANLEEUWEN"/><ref name="PERRYMAN">
{{cite journal
|last=Perryman |first=M. A. C.
|coauthors=''et al.''
|year=1997
|title=The Hipparcos Catalogue
|journal=[[Astronomy and Astrophysics Letters]]
|volume=323 |pages=L49–L52
|bibcode=1997A&A...323L..49P
|doi=
|quote=The original parallax figure from the [[Hipparcos Catalogue]] as shown in the [[SIMBAD]] astronomical database was 8.42 ± 0.86[[milliarcsecond|mas]] yielding a distance of about 119 ± 1.0pc or 388 ± 3.2ly
}}</ref><ref name="HUBBLENEWS">
{{cite web
|last=Weaver |first=D.
|last2=Soderblom |first2=D.
|title=Hubble Refines Distance to Pleiades Star Cluster
|url=http://hubblesite.org/newscenter/archive/releases/2004/20/text/
|publisher=Hubblesite Newscenter
|date=1 June 2004
|accessdate=2010-09-13
}}</ref> If the Hipparcos estimate were accurate, some astronomers contend, then stars in the cluster would have to be fainter than Sun-like stars&mdash;a notion that would challenge some of the fundamental precepts of stellar structure. [[Interferometric]] measurements taken in 2004 by the [[Hubble Space Telescope|Hubble Telescope]]'s [[Fine Guidance Sensor]]s and corroborated by studies from [[Caltech]] and [[NASA]]'s [[Jet Propulsion Laboratory]] showed the original estimate of 135 [[parsec|pc]] or 440 [[light year|ly]] to be the correct figure.<ref name="HUBBLENEWS"/> However a recent study published in 2009 has argued otherwise, publishing a new parallax measurement of 8.32 [[milliarcsecond|mas]] with a very tight error factor of 0.13 [[milliarcsecond|mas]] yielding a distance of 120.2 ± 1.9 [[parsec|pc]] or 392.0 ± 6.0 [[Light year|ly]].<ref name="VANLEEUWEN"/> Which distance estimate future [[astrometric]] calculations will corroborate remains to be seen, although the upcoming [[Gaia mission]] with its expected launch in late 2012 could well prove to be the ultimate arbiter in this debate.<ref name="ESA">
{{cite web
|title=Gaia overview
|url=http://www.esa.int/esaSC/120377_index_0_m.html
|publisher=[[European Space Agency]]
|date=4 May 2010
|accessdate=2010-09-14
}}</ref>
 
==Properties==
In 1942 [[Otto Struve]], one of the early researchers of Be Stars, stated that Pleione is "the most interesting member of the [[Pleiades]] cluster".<ref name="STRUVE">
{{cite journal
|last=Struve |first=O.
|year=1943
|title=The Story of Pleione
|journal=[[Popular Astronomy (US magazine)|Popular Astronomy]]
|volume=51 |page=233
|bibcode=1943PA.....51..233S
}}</ref> Like many of the stars in the [[open cluster|cluster]], Pleione is a blue-white [[stellar classification|B-type]] [[main sequence]] [[dwarf star]] with a temperature of about 12,000 [[Kelvin]].<ref name="STEE"/> It has a [[bolometric luminosity]] of 190 [[Solar luminosity|L<sub>☉</sub>]] assuming a distance of roughly 120 [[parsec|pc]].<ref name="KALER" /> With a radius of 3.2 [[Solar radius|R<sub>☉</sub>]] and mass that is 3.4 [[Solar mass|M<sub>☉</sub>]], Pleione is considerably smaller than the brightest stars in the Pleiades.<ref name="KALER"/> [[Alcyone (star)|Alcyone]] for instance has a radius that is 10 [[Solar radius|R<sub>☉</sub>]] with a luminosity 2,400 [[Solar luminosity|L<sub>☉</sub>]], making it roughly 30 times more voluminous than Pleione and about 13 times brighter.<ref name="NOTEALCYONE" group="note">The relative size of Alcyone (''V''<sub>A</sub>) compared to Pleione (''V''<sub>P</sub>) is determined by comparing their [[Volume of a sphere|volumes]]. It is assumed that the volume of each star is reasonably approximated by the formula for a [[sphere]]:
:''V''<sub>A</sub> ≈ {{frac|4|3}}π × 10<sup>3</sup> ≈ 4,188.79 ''V''<sub>Sun</sub>
:''V''<sub>P</sub> ≈ {{frac|4|3}}π × 3.2<sup>3</sup> ≈ 137.26 ''V''<sub>Sun</sub>
Therefore, the volume of Alcyone compared to Pleione ≈ 4,188.79 ÷ 137.26 ≈ 30.52
 
Alcyone's luminosity compared to Pleione is:
:2,400[[Solar luminosity|L<sub>☉</sub>]] ÷ 190[[Solar luminosity|L<sub>☉</sub>]] = 12.63 (or 13 rounded)<br></ref>
 
===Be star===
Pleione is a classical [[Be star]], often referred to as an "active hot star".<ref name="STEE">
{{cite web
|last=Stee |first=P.
|title=What is a Be star?
|work=Hot and Active Stars Research
|url=http://www.oca.eu/stee/page1/page3/page3.html
|accessdate=2010-06-20
}}</ref> Classical Be stars are B-type stars close to the main sequence with an "e" added on, signifying that Pleione exhibits [[spectral line|'''e'''mission lines]] in its [[spectrum]] rather than [[spectroscopy|absorption lines]], which is what stars usually show.<ref name="BADASTRONOMY">
{{cite web
|last=Plait |first=P.
|date=5 August 2009
|url=http://blogs.discovermagazine.com/badastronomy/2009/08/05/to-be-or-not-to-be/
|title=<nowiki>To B[e] or not to B[e]</nowiki>
|work=[[Bad Astronomy]]
|accessdate=2010-09-20
}}</ref> Emission lines usually indicate that a star is surrounded by gas. In the case of a Be star, the gas is typically in the form of an [[circumstellar disk|equatorial disk]], resulting in [[electromagnetic radiation]] that emanates not just from the [[photosphere]], but from the disk as well. The geometry and [[kinematics]] of this gaseous circumstellar environment are therefore best explained by a "Keplerian" disk&mdash;one that is supported against gravity by rotation rather than gas or radiation pressure.<ref name="PORTER">
{{cite journal
|last=Porter |first=J. M.
|last2=Rivinius |first2=T.
|year=2003
|title=Classical Be Stars
|journal=[[Publications of the Astronomical Society of the Pacific]]
|volume=115 |issue=812 |pages=1153–1170
|bibcode=2003PASP..115.1153P
|doi=10.1086/378307
}}</ref><ref name="SPACEREF"/> Circumstellar disks like this are sometimes referred to as ''"decretion disks"'', which is material being actively ejected by the star as opposed to ''"accretion disks"'' which involves material falling toward the star.<ref name="THIZY">
{{cite web
|last=Thizy |first=O.
|title=Be Stars
|url=http://www.shelyak.com/en/be_stars.html
|publisher=[[Shelyak Instruments]]
|accessdate=2010-06-20
}}</ref>
 
[[File:Classical Be star.jpg|thumb|left|Artist's impression of the [[Phi Persei]] system. Classical [[Be star]]s like Pleione and Phi Persei exhibit gaseous equatorial disks, likely caused by [[Stellar rotation|rapid rotation]].<ref name="LEHIGH">
{{cite web
|title=Classical Be Stars
|url=http://www.lehigh.edu/~mvm207/research.html
|work=Research in Astronomy & Astrophysics at Lehigh
|publisher=[[Lehigh University]]
|accessdate=2010-09-16
}}</ref>]]
 
Be Stars are [[Stellar rotation|fast rotators]] (>200&nbsp;km/s) with a large [[stellar wind]] and high [[Stellar mass loss|mass loss]] rate, hence the causative factors behind these gaseous rings.<ref name="STEE"/> Due to its apparent brightness, the star most recognized for its fast rotation is [[Achernar]], a phenomenon which causes it to be highly [[Flattening|oblate]]. Its rotational velocity, however, of 251&nbsp;km/s is considerably slower than Pleione's 329&nbsp;km/s.<ref name="HR1" /><ref name="HR2">
{{cite web
|title=HR 20472
|url=http://vizier.u-strasbg.fr/viz-bin/VizieR-S?HR%20472
|work=Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991)
|publisher=[[VizieR]], [[Centre de Données astronomiques de Strasbourg]]
|accessdate=2010-06-20
}}</ref> As a result, Pleione actually revolves on its axis once every 11.8 hours compared to Achernar's 48.4 hours.<ref name="NOTEROTATION" group="note">The time it takes for Achernar (''T''<sub>A</sub>) and Pleione (''T''<sub>P</sub>) to rotate on its own axis is determined by taking the star's radius in solar units, multiplying by the Sun's radius in kilometers, then calculating the star's circumference at the equator and dividing by its speed of rotation ''per hour''. Therefore:
:''T''<sub>A</sub> = 10 R<sub>☉</sub> × 696,000 km × 2 × π ÷ 251 km/s ÷ 3,600 ≈ 48.4 hrs
:''T''<sub>P</sub> = 3.2 R<sub>☉</sub> × 696,000 km × 2 × π ÷ 329 km/s ÷ 3,600 ≈ 11.8 hrs</ref> The [[Sun]] by comparison takes 25.3 days to turn on its axis. Pleione is spinning so fast that it is close to the estimated [[breakup velocity]] for a B8V star of about 370–390&nbsp;km/s.<ref name=" HIRATA1"/> Another Be star whose rotational velocity is extremely fast is [[Alpha Arae]] at 470&nbsp;km/s&mdash;a speed so extreme that it is on the verge of exploding.<ref name="ESO0635">
{{cite press
|last=Getsova |first=I.
|coauthors=''et al.''
|title=To Be or Not to Be: Is It All About Spinning?
|date=20 September 2006
|publisher=[[European Southern Observatory]]
|url=http://www.eso.org/public/news/eso0635/
|accessdate=2010-09-16
}}</ref>
 
What makes Pleione particularly unique is that it alternates between three different phases: 1) normal [[B star]], 2) [[Be star]] and 3) [[Shell star|Be shell star]].<ref name="KALER" /> The cause is likely the surrounding gaseous disk which in many Be stars will appear, then disappear, possibly reforming at a later time. Material in the disc is attracted back towards the star by the pull of gravity, but if it has enough energy it can escape into space, contributing to the [[stellar wind]].<ref name="SPACEREF">
{{cite web
|date=1 November 2002
|title=Glasgow astronomers explain hot star disks
|publisher=[[SpaceRef]]
|url=http://www.spaceref.com/news/viewpr.html?pid=9717
|accessdate=2010-06-20
}}</ref> Sometimes, Be stars will form multiple gas rings or "decretion disks", each with its own evolution, creating complex circumstellar dynamics.<ref name="TANAKA"/>
 
[[File:Alpha Arae.jpg|thumb|right|Artist's impression of [[Alpha Arae]] rotating with a velocity close to [[Stellar rotation#Equatorial bulge|breakup]] and losing mass through a [[stellar wind]] emerging from the poles.<ref name="ESO0635"/>]]
 
As a result of such dynamics, Pleione exhibits prominent long-term [[Photometry (astronomy)|photometric]] and [[spectroscopic]] variations encompassing a period of about 35 years.<ref name="TANAKA">
{{cite journal
|last=Tanaka |first=K.
|coauthors=''et al.''
|year=2007
|title=Dramatic Spectral and Photometric Changes of Pleione (28 Tau) between 2005 November and 2007 April
|journal=[[Publications of the Astronomical Society of Japan]]
|volume=59 |issue=4 |pages=L35–L39
|url=http://pasj.asj.or.jp/v59/n4/590404/590404.pdf
|format=PDF
|accessdate=2010-06-13
|doi=
|bibcode=2007PASJ...59L..35T
}}</ref> In fact, during the last 100 years, Pleione has demonstrated notable phase changes&mdash;as a Be phase until 1903, a B phase (1905–1936), a B-shell phase (1938–1954), and another Be phase (1955–1972).<ref name="HIRATA1">
{{cite journal
|last=Hirata |first=Ryuko
|year=1995
|title=Interpretation of the Long-Term Variation in Late-Type Active Be Stars
|journal=[[Publications of the Astronomical Society of Japan]]
|volume=47 |pages=195–218
|bibcode=1995PASJ...47..195H
}}</ref> It then entered a Be-shell phase in 1972. Then, the star developed many [[Shell star|shell]] [[Absorption spectroscopy|absorption lines]] in its spectrum. At the same time, the star showed a decrease in brightness, beginning at the end of 1971. After reaching the minimum brightness in late 1973, the star gradually brightened. In 1989, Pleione entered a Be phase and stayed as a Be star until the summer of 2005.<ref name="TANAKA" />
 
The most recent disk responsible for these phase changes was formed in 1972.<ref name="TANAKA"/> What's intriguing, however, is that Pleione's long-term [[Polarimetry|polarimetric]] observations show the intrinsic [[Brewster's angle|polarization angle]] has changed, providing direct evidence for a spatial motion of the disk axis.<ref name="HIRATA2">
{{cite journal
|last=Hirata |first=R.
|year=2007
|title=Disk Precession in Pleione
|journal=[[ASP Conference Series]]
|volume=361 |page=267
|bibcode=2007ASPC..361..267H
}}</ref> Because Pleione has a stellar companion with a relatively close orbit, the shift in the polarization angle has been attributed to the companion causing a [[precession]] (wobble) of the disk, with a precession period of roughly 81 years.<ref name="HIRATA2"/>
 
Recent photometric and spectroscopic observations from 2005 to 2007 indicate that a new disk has formed around the equator&mdash;thus constituting a double disk phenomenon with disks at different angles.<ref name="TANAKA"/><ref name="HIRATA2"/> The inclination angle of the new disk is estimated at 60° whereas the previous disk was inclined at around 30°. Such a misaligned double-disk structure has never been observed before among Be stars. Thus, Pleione provides a rare opportunity to investigate the forming process of a new disk and the consequent interaction between the two.<ref name="TANAKA"/><ref name="HIRATA2"/>
 
==Star system==
Pleione is known to be a [[Speckle imaging|speckle]] [[Binary star|binary]], although its orbital parameters have yet to be fully established.<ref name="MCALISTER">
{{cite journal
|last=McAlister |first=H. A.
|coauthors=''et al.''
|year=1989
|title=ICCD speckle observations of binary stars. IV - Measurements during 1986-1988 from the Kitt Peak 4 M telescope
|journal=[[Astronomical Journal]]
|volume=97 |pages=510–531
|bibcode=1989AJ.....97..510M
|doi=10.1086/115001
}}</ref> In 1996 a group of Japanese and French astronomers discovered that Pleione is a single-lined [[spectroscopic binary]] with an [[orbital period]] of 218.0 days and a large [[Orbital elements|eccentricity]] of 0.6.<ref name="TANAKA" /><ref name="KATAHIRA">
{{cite journal
|author1=Katahira, Jun-Ichi
|last=Katahira, J.-I.
|coauthors=''et al.''
|year=1996
|title=Period Analysis of the Radial Velocity in PLEIONE
|journal=[[Publications of the Astronomical Society of Japan]]
|volume=48 |pages=317–334
|bibcode=1996PASJ...48..317K
}}</ref> The [[Washington Double Star Catalogue]] lists an angular separation between the two components of 0.2 [[arcseconds]]&mdash;an angle which equates to a distance of about 24 [[Astronomical Units|AU]], assuming a distance of 120 parsecs.<ref name="ALCYONE">
{{cite web
|last=Mason |first=B. D.
|coauthors=''et al.''
|year=1996
|title=Pleione
|url=http://www.alcyone.de/SIT/mainstars/SIT000781.htm
|publisher=Alcyone (Star Information Tool)
|accessdate=2010-09-21
}}</ref>
 
==Ethnological influences==
[[File:Les Oceanides Les Naiades de la mer.jpg|thumb|right|260px|Depiction of Pleione as an [[Oceanid]] [[nymph]]. Painting from French artist [[Gustave Doré]].]]
 
===Mythology===
{{Main|Pleione (mythology)}}
Pleione was an [[Oceanid]] [[nymph]] of Mount Kyllene in Arkadia (southern Greece), one of the three thousand daughters of the [[Titan (mythology)|Titans]] [[Oceanus]] and [[Tethys (mythology)|Tethys]].<ref name="ANDREWS">
{{cite book
|last=Andrews |first=M.
|year=2004
|title=The Seven Sisters of the Pleiades - Stories from around the world
|url=http://books.google.com/?id=3GbYg26S8pUC&lpg=PA61&dq=pleione%20sailing&pg=PA61#v=onepage&q=pleione%20sailing&f=false
|publisher=[[Spinifex Press]]
|isbn=1-876756-45-4
|accessdate=2010-10-07
}}</ref><ref name="SMITH"/> The nymphs in [[Greek mythology]] were the spirits of nature; oceanids, spirits of the sea.<ref name="ATHENA">
{{cite web
|last=Athena |first=A.
|date=8 July 2010
|title=Nymphs
|url=http://www.paleothea.com/Nymphs.html
|work=Women in Greek Myths
|accessdate=2010-10-07
}}</ref> Though considered lesser divinities, they were still very much venerated as the protectors of the natural world. Each oceanid was thence a patroness of a particular body of water &mdash; be it ocean, river, lake, spring or even cloud &mdash; and by extension activities related thereto. The sea-nymph, Pleione, was the consort of [[Atlas (mythology)|Atlas]], the [[Titan (mythology)|Titan]], and mother of the [[Hyas]], [[Hyades (mythology)|Hyades]] and [[Pleiades (Greek mythology)|Pleiades]].<ref name="FRAZER"/>
 
===Etymology===
When names were assigned to the stars in the Pleiades cluster, the bright pair of stars in the East of the cluster were named Atlas and Pleione, while the seven other bright stars were named after the [[mythology|mythological]] Pleiades (the 'Seven Sisters'). The term "Pleiades" was used by [[Gaius Valerius Flaccus|Valerius Flaccus]] to apply to the cluster as a whole, and [[Giovanni Battista Riccioli|Riccioli]] called the star ''Mater Pleione''.<ref name="ALLEN">
{{cite web
|last=Allen |first=R. H.
|year=1963
|title=Star Names: Their Lore and Meaning
|url=http://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/Taurus*.html
|page=408
|publisher=[[Dover Publications]]
|accessdate=2010-06-11
}}</ref>
 
There is some diversity of opinion as to the origin of the names Pleione and Pleiades. There are three possible derivations of note. Foremost is that both names come from the Greek word πλεῖν, ''(pr. ple'-ō)'', meaning "to sail".<ref name="ALLEN"/><ref name="GIBSON">
{{cite web
|last=Gibson |first=S.
|date=5 April 2007
|title=Pleiades Mythology
|url=http://www.naic.edu/~gibson/pleiades/pleiades_myth.html
|publisher=[[National Astronomy and Ionosphere Center]]
|accessdate=2010-06-18
}}</ref> This is particularly plausible given that ancient Greece was a seafaring culture and because of Pleione's [[myth]]ical status as an Oceanid nymph. Pleione, as a result, is sometimes referred to as the "sailing queen" while her daughters the "sailing ones". Also, the appearance of these stars coincided with the sailing season in antiquity; sailors were well advised to set sail only when the Pleiades were visible at night, lest they meet with misfortune.<ref name=" FRAZER">
{{cite web
|author=Apollodorus
|coauthors=Frazer, J. G (transl.)
|year=1921
|title=Book 3, Chapter 10, Section 1
|url=http://www.perseus.tufts.edu/hopper/text?doc=Apollod.%203.10.1&lang=original
|work=[[Bibliotheca (Pseudo-Apollodorus)|The Library]]
|publisher=
|accessdate=2010-06-17
}}</ref>
 
Another derivation of the name is the Greek word Πλειόνη<ref name="SMITH">
{{cite web
|last=Smith |first=W.
|year=1873
|title=Plei'one
|work=A dictionary of Greek and Roman biography and mythology
|publisher=[[John Murray (publisher)|John Murray]]
|url=http://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:1999.04.0104:entry=pleione-bio-1
|accessdate=2010-06-17
}}</ref> ''(pr. plêionê)'', meaning "more", "plenty", or "full"&mdash;a [[lexeme]] with many [[List of Greek words with English derivatives#Π|English derivatives]] like [[pleiotropy]], [[wikt:pleomorphism|pleomorphism]], [[pleonasm]], [[pleonexia]], [[wiktionary:plethora|plethora]] and [[Pliocene]]. This meaning also coincides with the biblical Kīmāh and the Arabic word for the Pleiades — Al Thurayya.<ref name=" ALLEN " /> In fact, Pleione may have been numbered amongst the [[Epimelides]] (nymphs of meadows and pastures) and presided over the multiplication of the animals, as her name means "to increase in number".<ref name="THEOI">
{{cite web
|last=Atsma |first=A. J.
|date=8 March 2010
|url=http://www.theoi.com/Nymphe/NymphePleione.html
|title=Pleione
|publisher=Theoi Greek Mythology
|accessdate=2010-06-14
}}</ref>
 
Finally, the last comes from [[Peleiades]] ([[Ancient Greek|Greek]]: {{lang|grc|Πελειάδες}}, "[[dove]]s"), a reference to the sisters' mythical transformation by [[Zeus]] into a flock of doves following their pursuit by [[Orion (mythology)|Orion]], the [http://antwrp.gsfc.nasa.gov/apod/ap100329.html giant huntsman], across the heavens.<ref name="HESIOD">
{{cite book
|author=[[Hesiod]]
|coauthors=Evelyn-White, H. G. (transl.)
|year=1914
|chapter=ll. 618-640
|title=Works and Days
|url=http://www.sacred-texts.com/cla/hesiod/works.htm
|publisher=The Internet Sacred Text Archive
|accessdate=2010-10-13
|isbn=0-585-30250-2
}}</ref>
 
===Modern legacy===
In the best-selling 1955 [[nature]] book published by [[Time-Life]] called ''[[The World We Live In]]'', there is an artist's impression of Pleione entitled ''Purple Pleione''.<ref>
{{cite book
|last=Barnett |first=L.
|year=1955
|title=[[The World We Live In]]
|publisher=[[Simon and Schuster]]
|page=284
}}</ref> The illustration is from the famed space artist [[Chesley Bonestell]] and carries the caption: "Purple Pleione, a star of the familiar Pleiades cluster, rotates so rapidly that it has flattened into a flying saucer and hurled forth a dark red ring of hydrogen. Where the excited gas crosses Pleione's equator, it obscures her violet light."
 
Given its mythical connection with [[sailing]] and [[Pleione (orchid)|orchid]]s, the name Pleione is often associated with grace, speed and elegance. Some of the finest designs in racing [[yacht]]s have the name Pleione,<ref name="DYSON">
{{cite web
|title=Team Pleione
|publisher=Marblehead International One Design Class
|url=http://ww.marbleheadiod.com/8mr/
|accessdate=2010-10-07
}}</ref><ref name="TAYLOR">
{{cite web
|last=Taylor |first=J.
|date=19 March 2009
|title=Fast Boats in the 'Spirit of Tradition'
|url=http://www.tayloryachtdesigns.com/yacht_design.php#post-33
|work=Jim Taylor Yacht Designs
|accessdate=2010-10-07
}}</ref> and the recent [[Shanghai Oriental Art Center]] draws its inspiration from an orchid.<ref name="CHAMI">
{{cite web
|last=Chami |first=C.
|date=9 January 2008
|title=Paul Andreu - The Oriental Arts Centre in Shanghai
|url=http://www.archinnovations.com/featured-projects/public-buildings/paul-andreu-the-oriental-arts-centre-in-shanghai/
|publisher=Archinnovations
|accessdate=2010-10-07
}}</ref> [[Fat Jon]] in his new [[album]] [[Hundred Eight Stars]] has a prismatic [[Track (CD)|track]] dedicated to 28 Tauri.<ref name="DISCOGS">
{{discogs release|id=998205|name=Hundred Eight Stars}}</ref>
 
==See also==
* [[Lists of stars]] in the constellation [[List of stars in Taurus|Taurus]]
* [[B star|Class B Stars]]
* [[Be stars]]
* [[Shell star]]
* [[Circumstellar disk]]
 
==Notes==
{{reflist|group=note}}
 
==References==
{{Reflist|colwidth=25em}}
 
==External links==
{{Commons category|Pleione (star)}}
*Jim Kaler's Stars, University of Illinois:[http://stars.astro.illinois.edu/sow/pleione.html PLEIONE (28 Tauri)]
* Philippe Stee's in-depth information on: [http://www.oca.eu/stee/page1/page3/page3.html Hot and Active Stars Research]
* Olivier Thizy's in-depth information on: [http://www.shelyak.com/en/be_stars.html Be Stars]
*High-resolution LRGB image based on 4 hrs total exposure: [http://www.perseus.gr/Astro-DSO-M45.htm M45 - Pleiades Open Cluster]
*[[Astronomy Picture of the Day|APOD]] Pictures:
# [http://antwrp.gsfc.nasa.gov/apod/ap100329.html Orion, the giant huntsman, in pursuit of the Pleiades]
# [http://antwrp.gsfc.nasa.gov/apod/ap091205.html Himalayan Skyscape]
# [http://antwrp.gsfc.nasa.gov/apod/ap090212.html Pleiades and the Milky Way]
# [http://antwrp.gsfc.nasa.gov/apod/ap071122.html Pleiades and the Interstellar Medium]
 
{{Stars of Taurus}}
{{Good article}}
 
<!-- location classification -->
 
<!-- /catalogue classification -->
 
{{DEFAULTSORT:Pleione (Star)}}
[[Category:Taurus (constellation)]]
[[Category:Pleiades Open Cluster]]
<!-- /location classification -->
<!-- type classification -->
[[Category:B-type main-sequence stars]]
[[Category:Be stars]]
[[Category:Shell stars]]
<!-- /type classification -->
<!-- catalogue classification -->
[[Category:Stars with proper names]]
[[Category:Flamsteed objects|Tauri, 28]]
[[Category:Objects named with variable star designations|Tauri, BU]]
[[Category:Henry Draper Catalogue objects|23862]]
[[Category:HR objects|1180]]
[[Category:Hipparcos objects|17851]]

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