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Be Stars

Be Stars. Nicholas De Lucca. Classification. Spectral Class B Emission lines IR excess Be Main sequence Post main sequence B[e] Supergiant Pre-main sequence Planetary nebulae. M45. Be Stars. First observed 1867 - Angelo Secchi (1818-1878) Active hot star

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Be Stars

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  1. Be Stars Nicholas De Lucca

  2. Classification • Spectral Class B • Emission lines • IR excess • Be • Main sequence • Post main sequence • B[e] • Supergiant • Pre-main sequence • Planetary nebulae

  3. M45

  4. Be Stars • First observed 1867 - Angelo Secchi (1818-1878) • Active hot star • 20% of all B stars, 60-70% in younger clusters • Oblate • Strong polar wind • High speed rotation

  5. γCassiopeia Spectrum - Hα

  6. γCassiopeia - Structure

  7. Variability • Short Term • A few minutes or days • Photosphere oscillations? • Medium Term • Few years • Moving density pattern • Long Term • Few decades • B -> Be -> Be Shell • Reason unknown

  8. Long Term Variation

  9. Long Term Variation

  10. Rotation • Keplerian • 0.5 Vc > V > 0.9 Vc • V > 300 km/s

  11. B[e] Stars • 1970’s • Lower circumstellar density • Allows forbidden emission • Higher IR excess • B[e] phenomenon versus B[e] Star • Regions of varying density

  12. B[e] Phenomenon Criteria • Balmer emission lines • Low excitation permitted emission lines • [FeII] and [OI] forbidden emission lines in the visual • Infrared excess

  13. Forbidden Emission Lines – HD 38489

  14. B[e] Supergiants • L > 104LSun • Lower cimcumstellar density due to much larger size • Dust forms near edge of disk

  15. Herbig AeB[e] Stars • Young Stellar Objects (YSO) • 2-8 MSun • Lack of nuclear burning

  16. B[e] Planetary Nebulae • Ionized red giant gas shells • MRG < 8-10 MSun • May have [OIII], [SIII], [NeIII]

  17. Summary • Emission Lines • Permissible and forbidden • Variability • Short, medium and long term • Circumstellar disk • Strong Wind • Fast Rotation

  18. References • 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 Astrophysics, v.340, p.117-128 (1998) • 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 Francisco: Astronomical Society of the Pacific, 2006., p.125 • Stee, P. Active Hot Stars. Observatoria de la Cote d’Azur. 1 Dec. 2006 <http://www.oca.eu/stee/Bemodel.html> • Percy, John. “Gamma Cassiopeiae.” Variable Stars. American Association of Variable Star Observers. Oct. 2001 <http://www.aavso.org/vstar/vsots/1001.shtml> • Buill, Christian. The Be Stars Atlas. 20 Oct. 2007 <http://www.astrosurf.com/buil/us/bestar.htm> • Jensen, Adam. AST 102. 2 Dec. 2006 <http://origins.colorado.edu/~jensenag/teaching/AST102> • Thinkquest. <http://library.thinkquest.org/19662/images/eng/pages/model-bohr-3.jpg>

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