Be Stars
description
Transcript of Be Stars
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Be StarsBe Stars
Nicholas De LuccaNicholas De Lucca
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ClassificationClassification
Spectral Class BSpectral Class B Emission linesEmission lines IR excessIR excess BeBe
Main sequenceMain sequence Post main sequencePost main sequence
B[e]B[e] SupergiantSupergiant Pre-main sequencePre-main sequence Planetary nebulaePlanetary nebulae
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M45M45
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Be StarsBe Stars
First observed 1867 - First observed 1867 - Angelo Secchi (1818-Angelo Secchi (1818-1878)1878)
Active hot starActive hot star 20% of all B stars, 60-20% of all B stars, 60-
70% in younger clusters70% in younger clusters OblateOblate Strong polar windStrong polar wind High speed rotationHigh speed rotation
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γγCassiopeia Spectrum - HCassiopeia Spectrum - Hαα
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γγCassiopeia - StructureCassiopeia - Structure
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VariabilityVariability
Short TermShort Term A few minutes or daysA few minutes or days Photosphere oscillations?Photosphere oscillations?
Medium TermMedium Term Few yearsFew years Moving density patternMoving density pattern
Long TermLong Term Few decadesFew decades B -> Be -> Be ShellB -> Be -> Be Shell Reason unknownReason unknown
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Long Term VariationLong Term Variation
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Long Term VariationLong Term Variation
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RotationRotation
KeplerianKeplerian
0.50.5 V Vcc > > VV > 0.9 > 0.9 VVcc VV > 300 km/s > 300 km/s r
GMmmV 2
2
1
r
GMmmVc 2
2
1
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B[e] StarsB[e] Stars
1970’s1970’s Lower circumstellar densityLower circumstellar density
Allows forbidden emissionAllows forbidden emission Higher IR excessHigher IR excess B[e] phenomenon versus B[e] StarB[e] phenomenon versus B[e] Star Regions of varying densityRegions of varying density
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B[e] Phenomenon CriteriaB[e] Phenomenon Criteria
Balmer emission linesBalmer emission lines Low excitation permitted emission linesLow excitation permitted emission lines [Fe[FeIIII] and [O] and [OII] forbidden emission lines in the ] forbidden emission lines in the
visualvisual Infrared excessInfrared excess
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Forbidden Emission Lines – HD 38489Forbidden Emission Lines – HD 38489
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B[e] SupergiantsB[e] Supergiants
LL > 10 > 1044LLSunSun Lower cimcumstellar Lower cimcumstellar
density due to much density due to much larger sizelarger size
Dust forms near edge of Dust forms near edge of diskdisk
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Herbig AeB[e] StarsHerbig AeB[e] Stars
Young Stellar Young Stellar Objects (YSO)Objects (YSO)
2-8 2-8 MMSunSun
Lack of nuclear Lack of nuclear burningburning
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B[e] Planetary NebulaeB[e] Planetary Nebulae
Ionized red giant gas shellsIonized red giant gas shells MMRGRG < 8-10 < 8-10 MMSunSun
May have [OMay have [OIIIIII], [S], [SIIIIII], [Ne], [NeIIIIII]]
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SummarySummary
Emission LinesEmission LinesPermissible and forbiddenPermissible and forbidden
VariabilityVariabilityShort, medium and long termShort, medium and long term
Circumstellar diskCircumstellar disk Strong WindStrong Wind Fast RotationFast Rotation
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ReferencesReferences Lamers, Henny J. G. L. M.; Zickgraf, Franz-Josef; de Winter, Dolf; Houziaux, Leo; Lamers, Henny J. G. L. M.; Zickgraf, Franz-Josef; de Winter, Dolf; Houziaux, Leo;
Zorec, Janez, "An improved classification of B[e]-type stars", Astronomy and Zorec, Janez, "An improved classification of B[e]-type stars", Astronomy and Astrophysics, v.340, p.117-128 (1998) Astrophysics, v.340, p.117-128 (1998)
Michaela Kraus, Marcelo Borges Fernandes, Francisco X. de Ara´ujo, Henny Michaela Kraus, Marcelo Borges Fernandes, Francisco X. de Ara´ujo, Henny J.G.L.M. Lamers, "The Compact Planetary Nebula B[e] Star Hen 2--90", San J.G.L.M. Lamers, "The Compact Planetary Nebula B[e] Star Hen 2--90", San Francisco: Astronomical Society of the Pacific, 2006., p.125Francisco: Astronomical Society of the Pacific, 2006., p.125
Stee, P. Stee, P. Active Hot StarsActive Hot Stars. Observatoria de la Cote d’Azur. 1 Dec. 2006 . Observatoria de la Cote d’Azur. 1 Dec. 2006 <http://www.oca.eu/stee/Bemodel.html><http://www.oca.eu/stee/Bemodel.html>
Percy, John. “Gamma Cassiopeiae.” Percy, John. “Gamma Cassiopeiae.” Variable StarsVariable Stars. American Association of . American Association of Variable Star Observers. Oct. 2001 <http://www.aavso.org/vstar/vsots/1001.shtml>Variable Star Observers. Oct. 2001 <http://www.aavso.org/vstar/vsots/1001.shtml>
Buill, Christian. Buill, Christian. The Be Stars AtlasThe Be Stars Atlas. 20 Oct. 2007 . 20 Oct. 2007 <http://www.astrosurf.com/buil/us/bestar.htm><http://www.astrosurf.com/buil/us/bestar.htm>
Jensen, Adam. Jensen, Adam. AST 102AST 102. 2 Dec. 2006 . 2 Dec. 2006 <http://origins.colorado.edu/~jensenag/teaching/AST102><http://origins.colorado.edu/~jensenag/teaching/AST102>
ThinkquestThinkquest. <http://library.thinkquest.org/19662/images/eng/pages/model-bohr-. <http://library.thinkquest.org/19662/images/eng/pages/model-bohr-3.jpg>3.jpg>