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The B Stars Trilogy

Dive into the world of B stars and discover their classifications, from optical to ultraviolet. Explore their importance in determining distances, ages, and the spiral structure of the Milky Way. Learn about the complications in classifying B stars and the role of rotation. Discover how ultraviolet observations and IUE spectra can help in classifying these peculiar stars. Finally, unravel the secrets of the weird, peculiar, and brilliant Be stars and B[e] stars.

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The B Stars Trilogy

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  1. The B Stars Trilogy Zach Hartman

  2. Outline • What are they good for? • How do we classify them? • Optical • Ultraviolet • How weird can they get? DSS/NASA

  3. A Fistful of B Stars

  4. Why do we care about B stars? • H II Regions • More common than O stars • First large scale classification surveys were of B stars • Morgan 1950s • Winds Hui Yang NASA

  5. B stars matter! • Used to determine distances and ages of nearby open clusters • Garrison • The spiral structure of the Milky Way • Radiative atmospheres made them perfect candidates for testing models HST

  6. What does “B stars” mean? • 18 Solar Masses • 50,000 K • 7 Solar Radii • L = 20,000 Solar Luminosity

  7. For a few B stars more Optical Edition

  8. How do we classify them? • Originally defined by presence of neutral He. • Peaks at B2 • This is not the case for all B stars. • Si III is also present • Along with H and Mg II

  9. Example of a B3V Harvard Website

  10. Temperature Classification • Use several line ratios and other lines • Si IV 4089/ Si III 4552 • Decreases • Mg II • Increases • Balmer line strength • increases dramatically

  11. O9V to B3V Lines we are looking at: Balmer Lines: H9, H8, Hε, Hδ, Hγ Si IV 4089 / Si III 4552 He I increases over course of early B-types. Mg II 4481 increases

  12. B3V to A0V Lines we are looking at: Balmer Lines: H9, H8, Hε, Hδ, Hγ Si IV 4089 / Si III 4552 He I decreases over course of late B-types. Mg II 4481 increase

  13. Complications • The Stark Effect • Interaction between electrons and ions causes Zeeman-like splitting • Electrical analogue of Zeeman splitting • Dominant broadening mechanism for Balmer and He I lines • With increasing luminosity, the He I lines narrow and become more shallow for early B stars. • For mid B stars, He I lines narrow and deepen. • Means an evolved B star can be confused with early B

  14. Stark effect in spectra

  15. Rotation • Broadens the lines • Two solutions • Use equivalent widths • Use rapidly rotating standards

  16. Luminosity Classifications • Early Type • Balmer and He I become narrow and shallow • O II (4070, 4076 4348 4416) all increase • Silicon is better • Not affected by CNO O II Hγ

  17. Luminosity Classifications • Late Types • Hard • O II weak • Can use N II 3995 • Balmer lines best choice • Iterative process • Fit He I profiles

  18. For a Few B Stars More Ultraviolet Edition

  19. Ultraviolet Observations • Space Instruments • Wanted to observe these stars at the peak of their Planck curves. • International Ultraviolet Explorer (IUE) • Heck et al. 1984 published a catalog of stars in the UV

  20. IUE Spectra of B Stars • UV is difficult because there are resonance lines from winds • C IV, Si IV, N V • To match MK classification use photospheric lines • Si II/III, C II/III, Al II/III

  21. Using IUE Spectra as T Classifier Si II Si III Si IV Si II CIII • Lines to Remember: • Si II 1264/Si III 1299 • Si II 1265/Si III 1342 • C II 1334,1335/ C III 1175 • Al II 1671 / Al III 1863

  22. Using IUE Spectra as T Classifier Si II Si III Si II • Lines to Remember: • Si II 1264/Si III 1299 • Si II 1265/Si III 1342 • C II 1334,1335/ C III 1175 • Al II 1671 / Al III 1863

  23. Using IUE Spectra as L Classifier • Early Type Lines: • Al III 1855 • Fe III lines • Si II • Why not Si IV or C IV?

  24. Using IUE Spectra as L Classifier • Late Type Lines: • Al III 1670 • Fe III • Si II 1265 • O I 1656

  25. The Weird, the Peculiar and the Brilliant

  26. The Weird

  27. Be Stars • B stars with emission in the Balmer lines • Achernar • Also emission in Fe II • Comes from a hot circumstellar gas disk • Formation mechanism unknown • Not Herbig Ae/Be Stars or supergiants • Pre-MS Stars

  28. Be and B Shell Star Classification • Two goals of classifying Be and B Shell stars • Get the spectral type of the star • Get the emission spectra • (Temperature class)(Luminosity class)(Emission class) • Emission spectra can be variable • Star spectra is constant

  29. Classifying Be Stars • Mild Be stars are easy • Little Hα or Hβ emission • For others: • He I or Mg II 4481 • Use line ratios • For extreme Be stars • Good Luck! • Intense Balmer Emission

  30. Types of Be Stars – Lesh classes • - No H emission, some H lines filled in • - Hβ has narrow emission, is still absorption line • - Hβ in emission • - Hγ has narrow emission • - Complete H emission spectrum • - Fe II lines at more prominent • - Extreme Be stars

  31. Be Star line profiles • Contain information about system • Dachs et al. 1986/1987 • 4 classes • Symmetric double peak • Wine bottle • Asymmetric • Shell

  32. Be Star line profiles • Hanuschik et al. 1996 • Symmetric (Class 1) • Anti-symmetric (Class 2) • Function of inclination and optical depth

  33. B Shell Spectra • Shell Spectrum instead of emission • Disk becomes shell • Deep, narrow cores in Balmer • Fe II and Ti II absorption lines

  34. B[e] stars • Goal same as for Be stars • Get underlying stars • Harder because photospheric line are hidden • Show forbidden lines in spectra • [Fe II] and [O II] • Strong IR excess • Multiple Situations • Broad category • Types of B[e] Stars: • B[e] supergiants (sgB[e]) • Pre-MS B[e] (HAeB[e]) • Pne B[e] (cPNB[e]) • Symbiotic B[e] (SymB[e]) • Unclassified B[e] (unclB[e])

  35. Types of B[e] Stars • Supergiant • LMC, SMC • cPNB[e] • B stars going into the PNe phase • HAeB[e] • Same as Herbig AeBe • Plus forbidden lines

  36. B[e] Stars • Symbiotic • Shows hot and cool components • Unclassified • The “shrug” class • Does not fit any criteria

  37. The Peculiar

  38. He-strong Stars • Early B • Strong He lines • Abnormally strong • σ Ori E • Strong C II 4267 • Some are variable • B fields • Most have strong B fields

  39. He-weak Stars • Late B • H lines used • 3 classes • Si stars • Enhanced Si II • PGa • Phosphorus-gallium stars • SrTi • Strontium-titanium stars

  40. HgMn Stars

  41. The Brilliant

  42. B stars in Advanced States • High Galactic Latitude Normal B stars • Faint blue stars • 5 possibilities • sdOB • Blue H Branch • Young stars in Halo • Pop 1 stars ejected from disk • Old evolved stars

  43. sdOB Stars • 2 groups • Stars at extreme end of Horizontal branch • Post PNe stars at tip of White dwarf sequence • Majority appear to be in close binaries • Some are known to pulsate as well Mochejska, B.J., APOD

  44. Spectral Classification • Set by Drilling et al. 2003 • Adds Helium class to T and L • T class set by line ratios • He I/He II • Si III/ Si II • He Class is function of He I, II and Hγ line strengths • 0 to 40 • No He to no H • L is either VI, VII, VIII • Line widths

  45. Spectral Classification • Set by Drilling et al. 2003 • Adds Helium class to T and L • T class set by line ratios • He I/He II • Si III/ Si II • He Class is function of He I, II and Hγ line strengths • 0 to 40 • No He to no H • L is either VI, VII, VIII • Line widths

  46. BINARIES!!!!!!!! UberBlink

  47. sdB + dM Binaries • Close binaries • Have periods from hours to days • More massive companion evolved and overflowed its Roche lobe • Envelope disappeared somehow

  48. Conclusions • B stars are very useful and need to be found • Spectral Classification depends on He, Si, and H lines in the Optical • Photospheric lines in the UV (Si, C, Al) • Many interesting and weird objects are B stars

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